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Jiang J, Du Z, Field RW. Determination of the sign of the population difference in a two-level system by frequency-modulation spectroscopy. Mol Phys 2020. [DOI: 10.1080/00268976.2019.1660007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Jun Jiang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Zhenhui Du
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin, People's Republic of China
| | - Robert W. Field
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
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2
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Lockhart JPA, Gross EC, Sears TJ, Hall GE. Kinetic study of the OH + ethylene reaction using frequency‐modulated laser absorption spectroscopy. INT J CHEM KINET 2019. [DOI: 10.1002/kin.21265] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
| | - Eisen C. Gross
- Department of ChemistryStony Brook University Stony Brook New York
| | - Trevor J. Sears
- Division of Chemistry, Brookhaven National Laboratory Upton New York
- Department of ChemistryStony Brook University Stony Brook New York
| | - Gregory E. Hall
- Division of Chemistry, Brookhaven National Laboratory Upton New York
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Kashimura T, Yabushita S. Importance of the Parallel Component of the Transition Moments to the 1Π 1 (5A') and 3Π 1 (3A') Excited States of ICN in the Ã-Band Photodissociation. J Phys Chem A 2019; 123:4000-4013. [PMID: 30990688 DOI: 10.1021/acs.jpca.9b01127] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
ICN is one of the few simple triatomic molecules whose photodissociation mechanisms have been thoroughly investigated. Since it has a linear structure in the electronic ground state, the dissociation follows a photoexcitation at a linear or slightly bent structure. It is generally believed that the Ã-band consists of the dominant excitation to 3Π0+ (4A') with the transition dipole moment (TDM) parallel to the molecular axis ( z), a slightly weaker transition to 1Π1 (5A', 4A″), and a much weaker transition to 3Π1 (3A', 2A″), both of the latter two having perpendicular TDMs. In the present work, we have theoretically studied the geometry dependence of these TDMs and found a pronounced θ (bending angle) dependence in the parallel ( z) component of the TDMs to 1Π1 (5A') and 3Π1 (3A'), both of which should be zero at a linear geometry by symmetry and thus have been previously ignored. We estimated that the z component TDM to 1Π1 (5A') has a contribution of 15-20% to the total absorption cross-section at 249 nm at room temperature. Interestingly, the TDM to 3Π0+ (4A') does not exhibit such θ dependency and thus has only the z component. We compare the TDMs of ICN and CH3I molecules having similar excited states. The fact that all the TDMs to 3A', 4A', and 5A' have nonnegligible z components implies the importance of the coherent excitation contributions to various observables of CN fragment, such as the anisotropy parameter, the orientation parameter, and the rotational level distribution as well as the rotational fine structure level distribution.
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Affiliation(s)
- Tatsuhiko Kashimura
- Department of Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi, Kohoku-ku , Yokohama 223-8522 , Japan
| | - Satoshi Yabushita
- Department of Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi, Kohoku-ku , Yokohama 223-8522 , Japan
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Kashimura T, Ikezaki T, Ohta Y, Yabushita S. Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F 1 and F 2 spin-rotation levels of the CN products. J Comput Chem 2019; 40:482-499. [PMID: 30511401 DOI: 10.1002/jcc.25736] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Revised: 09/27/2018] [Accepted: 09/28/2018] [Indexed: 11/11/2022]
Abstract
One of the most spectacular yet unsolved problems for the ICN A ~ -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N - 1/2 populations for each rotation level N of the CN fragment. The F1 /F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2 P3/2 ) and I (2 P1/2 ) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen-Zener-Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A' and 4A' electronic states, and with a four-state model including the 3A' through 6A' electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's group and Hall's group, respectively. © 2018 Wiley Periodicals, Inc.
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Affiliation(s)
- Tatsuhiko Kashimura
- Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
| | - Tomoya Ikezaki
- Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
| | - Yusuke Ohta
- Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
| | - Satoshi Yabushita
- Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
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5
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Lockhart JP, Gross EC, Sears TJ, Hall GE. Investigating the photodissociation of H2O2 using frequency modulation laser absorption spectroscopy to monitor radical products. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2018.09.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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6
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Li C, Shao L, Meng H, Wei J, Qiu X, He Q, Ma W, Deng L, Chen Y. High-speed multi-pass tunable diode laser absorption spectrometer based on frequency-modulation spectroscopy. OPTICS EXPRESS 2018; 26:29330-29339. [PMID: 30470098 DOI: 10.1364/oe.26.029330] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Accepted: 09/28/2018] [Indexed: 06/09/2023]
Abstract
We report a multi-pass tunable diode laser absorption spectrometer based on the frequency-modulation spectroscopy (FMS) technique. It has the advantage of high scan speed and is immune to the etalon effect. A multi-pass Herriott-type cell was used in the spectrometer to increase the effective optical length to 17.5 m and compact the physical dimensions of the spectrometer to 60×30×30 cm3. Noise due to low-frequency fluctuation of the laser power and the 1/f noise in the rapid detection are sufficiently reduced by FMS. Interference fringes are effectively suppressed when the modulation frequency equals to integer or half-integer times of their free spectral range (FSR). An absorption line of C2H2 around 1.51 µm was recorded with the spectrometer to demonstrate its capabilities. The response frequency of the spectrometer is up to 100 kHz (10 µs) thanks to the high modulation frequency of FMS. The detection sensitivity of the spectrometer is about 240 ppb (3σ) at 100 kHz measurement repetition rate. The amplitude of the absorption signal is highly linear to the C2H2 concentration in the range of 300 ppb -100 ppm. Based on the Allan variation, the detection limit was determined to be 18 ppb with a detection time of 166 s.
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Forthomme D, Hause ML, Yu HG, Dagdigian PJ, Sears TJ, Hall GE. Doppler-Resolved Kinetics of Saturation Recovery. J Phys Chem A 2015; 119:7439-50. [PMID: 25815527 DOI: 10.1021/acs.jpca.5b00628] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Frequency-modulated laser transient absorption has been used to monitor the ground-state rotational energy-transfer rates of CN radicals in a double-resonance, depletion recovery experiment. When a pulsed laser is used to burn a hole in the equilibrium ground-state population of one rotational state without velocity selection, the population recovery rate is found to depend strongly on the Doppler detuning of a narrow-band probe laser. Similar effects should be apparent for any relaxation rate process that competes effectively with velocity randomization. Alternative methods of extracting thermal rate constants in the presence of these non-thermal conditions are evaluated. Total recovery rate constants, analogous to total removal rate constants in an experiment preparing a single initial rotational level, are in good agreement with quantum scattering calculations, but are slower than previously reported experiments and show qualitatively different rotational state dependence between Ar and He collision partners. Quasi-classical trajectory studies confirm that the differing rotational state dependence is primarily a kinematic effect.
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Affiliation(s)
- Damien Forthomme
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Michael L Hause
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Hua-Gen Yu
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Paul J Dagdigian
- ‡Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Trevor J Sears
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States.,§Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Gregory E Hall
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
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8
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Suter M, Quack M. Line shape of amplitude or frequency-modulated spectral profiles including resonator distortions. APPLIED OPTICS 2015; 54:4417-4431. [PMID: 25967497 DOI: 10.1364/ao.54.004417] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 04/07/2015] [Indexed: 06/04/2023]
Abstract
We report experiments and an improved method of analysis for any harmonics of frequency-modulated spectral line shapes allowing for very precise determinations of the resonance frequency of single absorption lines for gigahertz spectroscopy in the gas phase. Resonator perturbations are implemented into the formalism of modulation spectroscopy by means of a full complex transmission function being able to model the asymmetrically distorted absorption line shapes for arbitrary modulation depths, modulation frequencies, and resonator reflectivities. Exact equations of the in-phase and the quadrature modulation signal, taking into account a full resonator transmission function, are simultaneously adjusted to two-channel lock-in measurements performed in the gigahertz regime to obtain the spectral line position. The determination of the absorption line position of the rotational transition J' = 7 ← J" = 6 of (16)O(12)C(32)S in the vibrational ground state is investigated while changing the resonator distortions. The results are subjected to the approach proposed here and compared to standard methods known from the literature.
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Forthomme D, McRaven CP, Sears TJ, Hall GE. Argon-Induced Pressure Broadening, Shifting, and Narrowing in the CN A2Π–X2Σ+ (1–0) Band. J Phys Chem A 2013; 117:11837-46. [DOI: 10.1021/jp4030359] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Damien Forthomme
- Chemistry
Department, Brookhaven National Laboratory, Upton, New York 11973-5000,
United States
| | - Christopher P. McRaven
- Chemistry
Department, Brookhaven National Laboratory, Upton, New York 11973-5000,
United States
| | - Trevor J. Sears
- Chemistry
Department, Brookhaven National Laboratory, Upton, New York 11973-5000,
United States
- Department
of Chemistry, Stony Brook University, Stony
Brook, New York 11794,
United States
| | - Gregory E. Hall
- Chemistry
Department, Brookhaven National Laboratory, Upton, New York 11973-5000,
United States
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Paterson G, Costen ML, McKendrick KG. Collisional depolarisation of rotational angular momentum: influence of the potential energy surface on the collision dynamics? INT REV PHYS CHEM 2012. [DOI: 10.1080/0144235x.2012.659046] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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11
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Ciaffoni L, Peverall R, Ritchie GAD. Laser spectroscopy on volatile sulfur compounds: possibilities for breath analysis. J Breath Res 2011; 5:024002. [PMID: 21593551 DOI: 10.1088/1752-7155/5/2/024002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
There is an emerging interest in the detection of volatile sulfur compounds (VSCs) in the breath environment, given their biological relevance as potential signatures of several pathological conditions. Particularly, laser-based spectroscopic sensors are candidates for conducting accurate breath diagnostics in clinical settings. With these aims in mind, the current status of VSC sensing via laser absorption spectroscopy is reviewed in this paper. Attention has been focused on the most promising exhaled markers of pathological conditions, namely hydrogen sulfide, carbonyl sulfide, methanethiol, carbon disulfide and dimethyl sulfide. Details of the most relevant spectroscopic studies conducted on such molecules are presented, together with suggestions on the future direction of this challenging analytical field.
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Affiliation(s)
- L Ciaffoni
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, UK
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12
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Hancock G, Richmond G, Ritchie GA, Taylor S, Costen ML, Hall GE. Frequency modulated circular dichroism spectroscopy: application to ICN photolysis. Mol Phys 2010. [DOI: 10.1080/00268971003649323] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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13
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Ballingall I, Rutherford MF, McKendrick KG, Costen ML. Elastic depolarization and polarization transfer in CN(A2Π,v= 4)+Ar collisions. Mol Phys 2010. [DOI: 10.1080/00268970903476670] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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14
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Friedrichs G. Sensitive Absorption Methods for Quantitative Gas Phase Kinetic Measurements. Part 1: Frequency Modulation Spectroscopy. Z PHYS CHEM 2009. [DOI: 10.1524/zpch.2008.222.1.1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Frequency modulation spectroscopy (FMS) and cavity ringdown spectroscopy (CRDS) are sensitive absorption based detection methods that have found widespread applications in gas phase reaction kinetics. In part 1 of this review, the theoretical foundations of FMS are addressed with a special emphasis on time-resolved quantitative measurements of concentration profiles. A complementary review of CRDS can be found in part 2 (Z. Phys. Chem. 222 (2008) 31–61). Practical aspects, possible pitfalls, attainable sensitivities, and modern trends are discussed. Kinetic studies based on FMS measurements as a time-resolved detection tool are briefly reviewed and a bibliography with more than a hundred entries is included to facilitate the access to the large body of original literature.
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15
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Hancock G, Richmond G, Ritchie GAD, Taylor S. Diode laser based studies of the UV photolysis of molecular iodine. Phys Chem Chem Phys 2009; 11:6415-23. [DOI: 10.1039/b906401j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Costen ML, Marinakis S, McKendrick KG. Do vectors point the way to understanding energy transfer in molecular collisions? Chem Soc Rev 2008; 37:732-43. [DOI: 10.1039/b618070c] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Estupiñán EG, Smith JD, Tezaki A, Klippenstein SJ, Taatjes CA. Measurements and Modeling of DO2 Formation in the Reactions of C2D5 and C3D7 Radicals with O2. J Phys Chem A 2007; 111:4015-30. [PMID: 17388267 DOI: 10.1021/jp067602a] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Time-resolved production of HO2 and DO2 from the reactions of nondeuterated and deuterated ethyl and propyl radicals with O2 are measured as a function of temperature and pressure in the "transition region" between 623 and 748 K using the technique of laser photolysis/long path frequency modulation spectroscopy. Experimental measurements, using both pulsed-photolytic Cl-atom-initiated oxidation of ethane and propane and direct photolysis of ethyl, n-propyl, and isopropyl iodides, are compared to kinetic models based on the results of time-dependent master equation calculations with ab initio characterization of stationary points. The formation of DO2 and HO2 from the subsequent reaction of the alkyl radicals with O2 is followed by infrared frequency modulation spectroscopy. The concentration of I atoms is simultaneously monitored by direct absorption of a second laser probe on the spin-orbit transition. The kinetic models accurately describe the time scale and amplitude of the DO2 and HO2 formation resulting from C2D5 + O2, n-C3D7 + O2, i-C3D7 + O2, and i-C3H7 + O2. Overall, a very good level of agreement is found between theory and experiments over a wide range of temperatures, pressures, and O2 concentrations. Good agreement is also found between previous literature studies and the theory presented in this work except in the case of the high-temperature rate coefficients for the reaction of i-C3H7 + O2 to form propene. A reinvestigation of the high-temperature kinetics of the i-C3H7 + O2 reaction appears warranted. The results from the present work suggest that the theory for formation of HO2 from the reactions of ethyl and both isomeric forms of propyl radicals with O2 are very well established at this time. It is hoped that these reactions can now form the groundwork for the study and interpretation of larger and more complex R + O2 systems.
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Affiliation(s)
- Edgar G Estupiñán
- Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969, USA
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18
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Costen ML, Hall GE. Coherent and incoherent orientation and alignment of ICN photoproducts. Phys Chem Chem Phys 2007; 9:272-87. [PMID: 17186071 DOI: 10.1039/b612131d] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report extended measurements of the rotational polarization and correlated angular distribution of CN photofragments from ICN photodissociation, with a particular emphasis on the creation and detection of molecular orientation with circularly-polarized light. Doppler profiles of the nascent photoproducts are measured by Frequency-Modulated (FM) transient absorption, and the resulting high signal-to-noise data are valuable for verifying the form of the angular correlations between the recoil velocity, the photofragment rotational angular momentum, and the space-fixed frame defined by the dissociation polarization. A space-fixed bipolar moment notation can be used for an unambiguous characterization of the maximal set of polarization properties that can be created with one-photon excitation and detected with one-photon Doppler-resolved absorption spectroscopy. Relating the observed polarization moments to the various coherent and incoherent, adiabatic and non-adiabatic mechanisms, that have been derived and verified extensively in the case of diatomic photodissociation to polarized atomic fragments, is not unambiguous in the case of diatomic fragments from triatomic precursors. Constraints among various polarization moments confirmed in the case of diatomic dissociation are not confirmed in this triatomic case, where the perpendicular transitions to non-degenerate A' and A'' components of a linear Omega = 1 state are qualitatively different from excitation to degenerate Omega = +/-1 states in a diatomic molecule.
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Affiliation(s)
- Matthew L Costen
- School of Engineering and Physical Sciences, William H. Perkin Building, Heriot-Watt University, Edinburgh, UK.
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20
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Alagappan A, Ballingall I, Costen ML, McKendrick KG, Paterson G. Efficiencies of state and velocity-changing collisions of superthermal CN A2Π with He, Ar, N2and O2. Phys Chem Chem Phys 2007; 9:747-54. [PMID: 17268687 DOI: 10.1039/b614965k] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Polarized laser photolysis of ICN is combined with saturated optical pumping to prepare state-selected CN Alpha(2)Pi (nu' = 4, J = 0.5, F(2), f) with a well-defined anisotropic superthermal speed distribution. The collisional evolution of the prepared state is observed by Doppler-resolved Frequency Modulated (FM) spectroscopy via stimulated emission on the CN Alpha(2)Pi-Chi(2)Sigma(+) (4,2) band. The phenomenological rate constants for removal of the prepared state in collisions with He, Ar, N(2) and O(2) are reported. The observed collision cross-sections are consistent with attractive forces contributing significantly for all the colliders with the exception of He. The collisional evolution of the prepared velocity distribution demonstrates that no significant back-transfer into the prepared level occurs, and that any elastic scattering is strongly in the forward hemisphere.
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Affiliation(s)
- Azhagammai Alagappan
- School of Engineering and Physical Sciences, William H Perkin Building, Heriot-Watt University, Edinburgh, UK
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21
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Hancock G, Hutchinson A, Peverall R, Richmond G, Ritchie GAD, Taylor S. 266 nm photolysis of CF3I and C2F5I studied by diode laser gain FM spectroscopy. Phys Chem Chem Phys 2007; 9:2234-9. [PMID: 17487320 DOI: 10.1039/b617414k] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Frequency modulated diode laser based absorption at 1.315 microm has been used to measure the Doppler lineshapes of the I((2)P(1/2)-(2)P(3/2)) transition in atomic iodine produced from the 266 nm photolysis of both CF(3)I and C(2)F(5)I. Wavelength resolved laser gain is seen following photolysis as excited iodine atoms ((2)P(1/2)) are produced with a quantum yield close to unity from photolysis of both parent molecules. Time resolved measurements were made and the nascent speed distribution and translational anisotropy parameter, beta were determined. Mean atomic speeds of 800 and 850 ms(-1), which correspond to 83 and 68% of the maximum possible kinetic energy release into the iodine photofragment, were determined for photolysis of CF(3)I and C(2)F(5)I, respectively. The nascent translational anisotropy parameter was found to be beta = 1.77 +/- 0.05 for CF(3)I and beta = 1.69 +/- 0.05 for C(2)F(5)I. These values are explicable in terms of parent rotational motion and non-adiabatic processes in the exit channel.
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Affiliation(s)
- G Hancock
- Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford, UK OX1 3QZ
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Komissarov AV, Lin A, Sears TJ, Hall GE. State-resolved thermalization of singlet and mixed singlet-triplet states of CH2. J Chem Phys 2006; 125:084308. [PMID: 16965013 DOI: 10.1063/1.2345364] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The role of mixed states in the collision-induced thermalization, intersystem crossing, and reactive loss of CH(2) (~a (1)A1) has been monitored using Doppler-resolved transient frequency modulation absorption spectroscopy. Singlet CH(2) is produced in a hot initial distribution of translation and rotational energy states in the 308 nm photodissociation of ketene in a large excess of argon. Collisions with Ar and ketene cool the translational and rotational degrees of freedom, while depleting the total singlet CH(2) population through reaction and intersystem crossing. Direct monitoring of the time-dependent populations of rotational levels containing mixed singlet and triplet character reveals a rapid interconversion between the two components, but no discernable difference between the kinetics of the pure singlet and mixed states at longer times.
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Alagappan A, Costen ML, McKendrick KG. Frequency modulated spectroscopy as a probe of molecular collision dynamics. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2006; 63:910-22. [PMID: 16495130 DOI: 10.1016/j.saa.2005.10.050] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Revised: 09/14/2005] [Accepted: 10/24/2005] [Indexed: 05/06/2023]
Abstract
We describe the application of frequency modulated spectroscopy (FMS) with an external cavity tuneable diode laser to the study of the scalar and vector properties of inelastic collisions. CN X(2)Sigma(+) radicals are produced by polarized photodissociation of ICN at 266 nm, with a sharp velocity and rotational angular momentum distribution. The collisional evolution of the distribution is observed via sub-Doppler FMS on the A(2)Pi-X(2)Sigma(+) (2,0) band. He, Ar, N(2), O(2) and CO(2) were studied as collider gases. Doppler profiles were acquired in different experimental geometries of photolysis and probe laser propagation and polarization, and on different spectroscopic branches. These were combined to give composite Doppler profiles from which the speed distributions and specific speed-dependent vector correlations could be determined. The angular scattering dynamics with species other than He are found to be very similar, dominated by backward scattering which accompanies transfer of energy between rotation and translation. The kinematics of collisions with He are not conducive to the determination of differential scattering and angular momentum polarization correlations. Angular momentum correlations show interesting differences between reactive and non-reactive colliders. We propose that this reflects differences in the potential energy surfaces, in particular, the nature and depth of attractive potential wells.
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Affiliation(s)
- Azhagammai Alagappan
- School of Engineering and Physical Sciences, William H. Perkin Building, Heriot-Watt University, Edinburgh, UK
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Taatjes CA. Uncovering the Fundamental Chemistry of Alkyl + O2Reactions via Measurements of Product Formation. J Phys Chem A 2006; 110:4299-312. [PMID: 16571032 DOI: 10.1021/jp056997f] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reactions of alkyl radicals (R) with molecular oxygen (O(2)) are critical components in chemical models of tropospheric chemistry, hydrocarbon flames, and autoignition phenomena. The fundamental kinetics of the R + O(2) reactions is governed by a rich interplay of elementary physical chemistry processes. At low temperatures and moderate pressures, the reactions form stabilized alkylperoxy radicals (RO(2)), which are key chain carriers in the atmospheric oxidation of hydrocarbons. At higher temperatures, thermal dissociation of the alkylperoxy radicals becomes more rapid and the formation of hydroperoxyl radicals (HO(2)) and the conjugate alkenes begins to dominate the reaction. Internal isomerization of the RO(2) radicals to produce hydroperoxyalkyl radicals, often denoted by QOOH, leads to the production of OH and cyclic ether products. More crucially for combustion chemistry, reactions of the ephemeral QOOH species are also thought to be the key to chain branching in autoignition chemistry. Over the past decade, the understanding of these important reactions has changed greatly. A recognition, arising from classical kinetics experiments but firmly established by recent high-level theoretical studies, that HO(2) elimination occurs directly from an alkylperoxy radical without intervening isomerization has helped resolve tenacious controversies regarding HO(2) formation in these reactions. Second, the importance of including formally direct chemical activation pathways, especially for the formation of products but also for the formation of the QOOH species, in kinetic modeling of R + O(2) chemistry has been demonstrated. In addition, it appears that the crucial rate coefficient for the isomerization of RO(2) radicals to QOOH may be significantly larger than previously thought. These reinterpretations of this class of reactions have been supported by comparison of detailed theoretical calculations to new experimental results that monitor the formation of products of hydrocarbon radical oxidation following a pulsed-photolytic initiation. In this article, these recent experiments are discussed and their contributions to improving general models of alkyl + O(2) reactions are highlighted. Finally, several prospects are discussed for extending the experimental investigations to the pivotal questions of QOOH radical chemistry.
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Affiliation(s)
- Craig A Taatjes
- Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969, USA
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Bood J, McIlroy A, Osborn DL. Measurement of the sixth overtone band of nitric oxide, and its dipole moment function, using cavity-enhanced frequency modulation spectroscopy. J Chem Phys 2006; 124:084311. [PMID: 16512720 DOI: 10.1063/1.2170090] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We applied cavity-enhanced frequency modulation absorption spectroscopy (also known as noise-immune cavity-enhanced optical heterodyne molecular spectroscopy) to perform high-resolution spectroscopy of the sixth overtone band of nitric oxide near 797 nm. By using novel high-bandwidth balanced detectors, baseline variations caused by residual amplitude modulation were significantly reduced. The ultrahigh sensitivity (2 x 10(-10) cm(-1) minimum detectable absorption at 1 Hz detection bandwidth) of our spectrometer allowed accurate measurements of 15 individual line intensities of P- and R-branch transitions in the 2Pi(1/2)-2Pi(1/2) subband. A vibrational transition moment of 3.09(6) muD+/-13% and Herman-Wallis coefficients of a = -0.0078(26) and b = 0.001 25(45) were found by fitting the line intensities. Based on our measured transition moment, and those of other transitions from the literature, a new parametrization for the electric dipole moment function (EDMF) of nitric oxide, valid for 0.91 < or = r < or = 1.74 A, has been extracted. The residuals of this fit demonstrate that the derived EDMF is the most accurate representation to date of the dipole moment function. The new EDMF will be valuable for accurate intensity prediction of transitions that cannot be easily measured experimentally.
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Affiliation(s)
- Joakim Bood
- Sandia National Laboratories, MS 9055, P.O. Box 969, Livermore, California 94551-0969, USA
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Kim Y, Hall GE, Sears TJ. AC Stark detection of optical–optical double resonance in CH2. Phys Chem Chem Phys 2006; 8:2823-5. [PMID: 16775636 DOI: 10.1039/b606526k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A new scheme for the detection of double resonance spectra of chemical intermediates involves negligible population transfer but the detection of electric field-induced energy shifts in unpopulated levels.
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Affiliation(s)
- Yangsoo Kim
- Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
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Zhang B, Shiu W, Lin JJ, Liu K. Mode correlation of product pairs in the reaction OH+CD4→HOD+CD3. J Chem Phys 2005; 122:131102. [PMID: 15847448 DOI: 10.1063/1.1885466] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The hydrogen abstraction reaction from methane by a hydroxyl radical produces two polyatomic molecules. Each product has several vibrational modes that characterize distinct, concerted motions of the constituent atoms of the molecule. This communication describes the first measurement that maps out the coincident information on how the mode of excitation of one product varies with that of the other co-product. Such information on mode correlation of product pairs is particularly appealing in that it provides intuitively a glimpse of the reaction paths by which the chemical transformation occurs.
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Affiliation(s)
- Bailin Zhang
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, P.O. Box 23-166, Taipei, Taiwan 106
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CostenCurrent address: School of En ML, Hall GE. Hyperfine quantum beats from photolytic orientation and alignment. Phys Chem Chem Phys 2005; 7:1408-13. [DOI: 10.1039/b419006h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Hall GE, Komissarov AV, Sears TJ. Doppler-Resolved Spectroscopy as an Assignment Tool in the Spectrum of Singlet Methylene. J Phys Chem A 2004. [DOI: 10.1021/jp0494133] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Gregory E. Hall
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
| | | | - Trevor J. Sears
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
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Zou P, Shu J, Sears TJ, Hall GE, North SW. Photodissociation of Bromoform at 248 nm: Single and Multiphoton Processes. J Phys Chem A 2004. [DOI: 10.1021/jp0310394] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Peng Zou
- Chemistry Department, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, Chemical Sciences Division, Lawrence Berkeley Laboratory, University of California, and Chemistry Department, University of California, Berkeley, California 94720, and Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
| | - Jinian Shu
- Chemistry Department, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, Chemical Sciences Division, Lawrence Berkeley Laboratory, University of California, and Chemistry Department, University of California, Berkeley, California 94720, and Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
| | - Trevor J. Sears
- Chemistry Department, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, Chemical Sciences Division, Lawrence Berkeley Laboratory, University of California, and Chemistry Department, University of California, Berkeley, California 94720, and Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
| | - Gregory E. Hall
- Chemistry Department, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, Chemical Sciences Division, Lawrence Berkeley Laboratory, University of California, and Chemistry Department, University of California, Berkeley, California 94720, and Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
| | - Simon W. North
- Chemistry Department, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, Chemical Sciences Division, Lawrence Berkeley Laboratory, University of California, and Chemistry Department, University of California, Berkeley, California 94720, and Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
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Lin JJ, Zhou J, Shiu W, Liu K. State-specific correlation of coincident product pairs in the F + CD4 reaction. Science 2003; 300:966-9. [PMID: 12738861 DOI: 10.1126/science.1083672] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
When a chemical reaction forms two molecular products, even if the state-resolved differential cross section (DCS) for each product is obtained individually, the coincident attributes of the coproducts are still lacking. We exploit a method that provides coincidence information by measuring the state-resolved, pair-correlated DCS. Exemplified by the reaction F + CD4 --> DF + CD3, a time-sliced ion velocity imaging technique was used to measure the velocity distribution of a state-selected CD3 product and to reveal the information of the coincident DF in a state-correlated manner. The correlation of different product state pairs shows a striking difference, which opens up a new way to unravel the complexity of a polyatomic reaction.
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Affiliation(s)
- Jim J Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica, Post Office Box 23-166, Taipei, Taiwan 106
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McGivern WS, North SW. Treatment of the K-quantum number in unimolecular reaction theory: insights from product correlations. J Am Chem Soc 2002; 124:14472-7. [PMID: 12452724 DOI: 10.1021/ja0273602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The connection between the K-quantum number and product correlations in the barrierless unimolecular dissociation of symmetric-top molecules is explored to establish a qualitative diagnostic for the treatment of the K-rotor dynamics in unimolecular reaction theory. We find that fragment scalar and vector correlations can provide guidance in this matter, and the photodissociation dynamics of thermal NCNO to form CN and NO at several dissociation wavelengths are presented to demonstrate the utility of this approach. The "goodness" of the K-quantum number can be related to the amount of energy in the conserved vibrational modes at the inner transition state. On the basis of measured correlated vibrational distributions, the K-quantum number is found to be approximately conserved at the inner transition state for the photodissociation of NCNO at 514, 520, and 526 nm. The methodology, involving a comparison of product distributions from the photodissociation of jet and thermal ensembles at identical wavelengths, is general and may be applied to previously studied systems that dissociate along barrierless potential energy surfaces, CF(3)NO and CH(2)CO. In addition, vector correlations serve as a means to probe the K-mixing at the outer transition state, and measured v-j correlations in the photodissociation of thermal NCNO are presented.
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Affiliation(s)
- W Sean McGivern
- Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77842, USA
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Hancock G, Kasyutich VL, Ritchie GAD. Single-tone frequency-modulation spectroscopy with frequency-doubled current-modulated diode laser light. OPTICS LETTERS 2002; 27:763-765. [PMID: 18007925 DOI: 10.1364/ol.27.000763] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We demonstrate and characterize the generation of single-tone frequency-modulated and frequency-doubled radiation at 400 MHz and 430 nm. We obtained the radiation at 430 nm by frequency doubling light from a current-modulated 860-nm diode laser, using noncritical type I phase matching in a KNbO(3) crystal. The optical spectrum of the doubled light was found to be in keeping with our expectations based on the measured frequency- and amplitude-modulation indices of the fundamental radiation. The experimentally measured diode laser and crystal parameters were used to simulate the in-phase and quadrature signals that would be observed in a single-tone frequency-modulation spectroscopy experiment.
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McGivern WS, North SW. Probing the nature of the K-rotor in unimolecular reactions: Scalar and vector correlations in the photodissociation of NCNO. J Chem Phys 2002. [DOI: 10.1063/1.1462581] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Yu HG, Gonzalez-Lezana T, Marr AJ, Muckerman JT, Sears TJ. Experimental and theoretical studies of the near-infrared spectrum of bromomethylene. J Chem Phys 2001. [DOI: 10.1063/1.1386812] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Taatjes CA, Hershberger JF. Recent progress in infrared absorption techniques for elementary gas-phase reaction kinetics. Annu Rev Phys Chem 2001; 52:41-70. [PMID: 11326058 DOI: 10.1146/annurev.physchem.52.1.41] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Sensitive and precise measurements of rate coefficients, branching fractions, and energy disposal from gas-phase radical reactions provide information about the mechanism of elementary reactions as well as furnish modelers of complicated chemical systems with rate data. This chapter describes the use of time-resolved infrared laser absorption as a tool for investigating gas-phase radical reactions, emphasizing the exploitation of the particular advantages of the technique. The reaction of Cl atoms with HD illustrates the complementarity of thermal kinetic measurements with molecular beam data. Measurements of second-order reactions, such as the self-reactions of SiH3 and C3H3 radicals, and determinations of product branching fractions in reactions such as CN + O2 rely on the wide applicability of infrared absorption and on the straightforward relationship of absorption to absolute concentration. Finally, investigations of product vibrational distributions, as in the CN + H2 reaction, provide additional insight into the details of reaction mechanisms.
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Affiliation(s)
- C A Taatjes
- Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969, USA.
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Li R, McGivern W, North SW. Temperature-dependent photodissociation dynamics of ICN at 262 nm. Chem Phys Lett 2001. [DOI: 10.1016/s0009-2614(00)01441-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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38
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Costen ML, Katayanagi H, Hall GE. State Correlations in the Unimolecular Dissociation of Ketene. J Phys Chem A 2000. [DOI: 10.1021/jp001389f] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Matthew L. Costen
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, and Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
| | - Hideki Katayanagi
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, and Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
| | - Gregory E. Hall
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, and Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
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