1
|
de Castro DG, Poveda LA, Crispim LWS, Ballester MY. Quasi-Classical Trajectory Study of NH( 3∑ -) + NH( 3∑ -) Reactive Collisions. J Phys Chem A 2019; 123:9113-9122. [PMID: 31573199 DOI: 10.1021/acs.jpca.9b08278] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A full-dimension quasi-classical trajectory study of collisions between two NH radicals is presented. Interatomic interactions are represented by a previously reported global six-dimensional potential energy surface for singlet electronic state of the N2H2 system. This study suggests that the formation of N2 from the collision of two NH radicals may occur via a one-step (NH + NH → N2 + H + H) or two-step (NH + NH → N2H + H → N2 + H + H) microscopic reaction mechanism. A fast vibrational energy redistribution is observed in the four-body complex in the latter mechanism. Excitation functions are presented and discussed. A variant of the vibrational energy quantum mechanical threshold method was used to correct the zero-point energy leakage in the classical calculations. The influence of reactant's rotational and vibrational energy on reactivity was investigated by state-specific calculations with one or both reactants excited. Reaction rate constants for the ground and some rotationally excited states are presented using an Arrhenius-Kooij-like functional form.
Collapse
Affiliation(s)
| | - Luis A Poveda
- Centro Federal de Educação Tecnológica de Minas Gerais , Belo Horizonte 36700-000 , MG , Brazil
| | | | | |
Collapse
|
2
|
Kłos J, McCrudden G, Brouard M, Perkins T, Seamons SA, Herráez-Aguilar D, Aoiz FJ. Experimental and theoretical studies of the Xe-OH(A/X) quenching system. J Chem Phys 2018; 149:184301. [PMID: 30441911 DOI: 10.1063/1.5051068] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
New multi-reference, global ab initio potential energy surfaces (PESs) are reported for the interaction of Xe atoms with OH radicals in their ground X2Π and excited A2Σ+ states, together with the non-adiabatic couplings between them. The 2A' excited potential features a very deep well at the collinear Xe-OH configuration whose minimum corresponds to the avoided crossing with the 1A' PES. It is therefore expected that, as with collisions of Kr + OH(A), electronic quenching will play a major role in the dynamics, competing favorably with rotational energy transfer within the 2A' state. The surfaces and couplings are used in full three-state surface-hopping trajectory calculations, including roto-electronic couplings, to calculate integral cross sections for electronic quenching and collisional removal. Experimental cross sections, measured using Zeeman quantum beat spectroscopy, are also presented here for comparison with these calculations. Unlike similar previous work on the collisions of OH(A) with Kr, the surface-hopping calculations are only able to account qualitatively for the experimentally observed electronic quenching cross sections, with those calculated being around a factor of two smaller than the experimental ones. However, the predicted total depopulation of the initial rovibrational state of OH(A) (quenching plus rotational energy transfer) agrees well with the experimental results. Possible reasons for the discrepancies are discussed in detail.
Collapse
Affiliation(s)
- J Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - G McCrudden
- The Department of Chemistry, The Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - M Brouard
- The Department of Chemistry, The Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - T Perkins
- The Department of Chemistry, The Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - S A Seamons
- The Department of Chemistry, The Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - D Herráez-Aguilar
- Faculty of Experimental Sciences, Francisco de Vitoria University (UFV), 28223 Pozuelo de Alarcón (Madrid), Spain
| | - F J Aoiz
- Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain
| |
Collapse
|
3
|
Sharples TR, Leng JG, Luxford TFM, McKendrick KG, Jambrina PG, Aoiz FJ, Chandler DW, Costen ML. Non-intuitive rotational reorientation in collisions of NO(A 2Σ+) with Ne from direct measurement of a four-vector correlation. Nat Chem 2018; 10:1148-1153. [DOI: 10.1038/s41557-018-0121-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 07/12/2018] [Indexed: 11/09/2022]
|
4
|
Price TJ, Hickman AP. Semiclassical analysis of jm → j'm' transitions in rotationally inelastic collisions in cell experiments. J Chem Phys 2018; 148:074105. [PMID: 29471636 DOI: 10.1063/1.4996877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Recent quantum calculations of rotationally inelastic collisions of NaK (A1Σ+) with He or Ar in a cell experiment are analyzed using semiclassical approximations valid for large quantum numbers. The results suggest a physical interpretation of jm → j'm' transitions based on the vector model and lead to expressions that explicitly involve the initial and final polar angles of the angular momentum of the target molecule. The relation between the polar angle θ and the azimuthal quantum number m links the semiclassical results for the change in polar angle (θ → θ') to quantum results for an m → m' transition. Analytic formulas are derived that relate the location and width of peaks in the final polar angle distribution (PAD) to the K-dependence of the coefficients dK(j, j'), which are proportional to tensor cross sections σK(j → j'). Several special cases are treated that lead to final PADs that are approximately Lorentzian or sinc functions centered at θ' = θ. Another interesting case, "angular momentum reversal," was observed in the calculations for He. This phenomenon, which involves a reversal of the direction of the target's angular momentum, is shown to be associated with oscillatory behavior of the dK for certain transitions. Finally, several strategies for obtaining the dK coefficients from experimental data are discussed.
Collapse
Affiliation(s)
- T J Price
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - A P Hickman
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| |
Collapse
|
5
|
Brouard M, Lawlor J, McCrudden G, Perkins T, Seamons SA, Stevenson P, Chadwick H, Aoiz FJ. An experimental study of OH(A 2Σ +) + H 2: Electronic quenching, rotational energy transfer, and collisional depolarization. J Chem Phys 2017; 146:244313. [PMID: 28668067 DOI: 10.1063/1.4989567] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Zeeman quantum beat spectroscopy has been used to determine the thermal (300 K) rate constants for electronic quenching, rotational energy transfer, and collisional depolarization of OH(A2Σ+) by H2. Cross sections for both the collisional disorientation and collisional disalignment of the angular momentum in the OH(A2Σ+) radical are reported. The experimental results for OH(A2Σ+) + H2 are compared to previous work on the OH(A2Σ+) + He and Ar systems. Further comparisons are also made to the OH(A2Σ+) + Kr system, which has been shown to display significant non-adiabatic dynamics. The OH(A2Σ+) + H2 experimental data reveal that collisions that survive the electronic quenching process are highly depolarizing, reflecting the deep potential energy wells that exist on the excited electronic state surface.
Collapse
Affiliation(s)
- M Brouard
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - J Lawlor
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - G McCrudden
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - T Perkins
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - S A Seamons
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - P Stevenson
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - H Chadwick
- Chemistry Research Laboratory, The Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - F J Aoiz
- Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain
| |
Collapse
|
6
|
Price T, Towne A, Talbi D, Hickman A. Semiclassical model for the distribution of final polar angles and m′ states in rotationally inelastic collisions. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2015.12.037] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
|
7
|
Sharples TR, Luxford TFM, Townsend D, McKendrick KG, Costen ML. Rotationally inelastic scattering of NO(A(2)Σ(+)) + Ar: Differential cross sections and rotational angular momentum polarization. J Chem Phys 2015; 143:204301. [PMID: 26627953 DOI: 10.1063/1.4935962] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present the implementation of a new crossed-molecular beam, velocity-map ion-imaging apparatus, optimized for collisions of electronically excited molecules. We have applied this apparatus to rotational energy transfer in NO(A(2)Σ(+), v = 0, N = 0, j = 0.5) + Ar collisions, at an average energy of 525 cm(-1). We report differential cross sections for scattering into NO(A(2)Σ(+), v = 0, N' = 3, 5, 6, 7, 8, and 9), together with quantum scattering calculations of the differential cross sections and angle dependent rotational alignment. The differential cross sections show dramatic forward scattered peaks, together with oscillatory behavior at larger scattering angles, while the rotational alignment moments are also found to oscillate as a function of scattering angle. In general, the quantum scattering calculations are found to agree well with experiment, reproducing the forward scattering and oscillatory behavior at larger scattering angles. Analysis of the quantum scattering calculations as a function of total rotational angular momentum indicates that the forward scattering peak originates from the attractive minimum in the potential energy surface at the N-end of the NO. Deviations in the quantum scattering predictions from the experimental results, for scattering at angles greater than 10°, are observed to be more significant for scattering to odd final N'. We suggest that this represents inaccuracies in the potential energy surface, and in particular in its representation of the difference between the N- and O-ends of the molecule, as given by the odd-order Legendre moments of the surface.
Collapse
Affiliation(s)
- Thomas R Sharples
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Thomas F M Luxford
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Dave Townsend
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Kenneth G McKendrick
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Matthew L Costen
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| |
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
Malenda RF, Price TJ, Stevens J, Uppalapati SL, Fragale A, Weiser PM, Kuczala A, Talbi D, Hickman AP. Theoretical calculations of rotationally inelastic collisions of He with NaK(A (1)Σ(+)): Transfer of population, orientation, and alignment. J Chem Phys 2015; 142:224301. [PMID: 26071704 DOI: 10.1063/1.4922161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have performed extensive calculations to investigate thermal energy, rotationally inelastic collisions of NaK (A(1)Σ(+)) with He. We determined a potential energy surface using a multi-reference configuration interaction wave function as implemented by the GAMESS electronic structure code, and we have performed coupled channel scattering calculations using the Arthurs and Dalgarno formalism. We also calculate the Grawert coefficients B(λ)(j, j') for each j → j' transition. These coefficients are used to determine the probability that orientation and alignment are preserved in collisions taking place in a cell environment. The calculations include all rotational levels with j or j' between 0 and 50, and total (translational and rotational) energies in the range 0.0002-0.0025 a.u. (∼44-550 cm(-1)). The calculated cross sections for transitions with even values of Δj tend to be larger than those for transitions with odd Δj, in agreement with the recent experiments of Wolfe et al. (J. Chem. Phys. 134, 174301 (2011)). The calculations of the energy dependence of the cross sections and the calculations of the fraction of orientation and alignment preserved in collisions also exhibit distinctly different behaviors for odd and even values of Δj. The calculations also indicate that the average fraction of orientation or alignment preserved in a transition becomes larger as j increases. We interpret this behavior using the semiclassical model of Derouard, which also leads to a simple way of visualizing the distribution of the angles between the initial and final angular momentum vectors j and j'. Finally, we compare the exact quantum results for j → j' transitions with results based on the simpler, energy sudden approximation. That approximation is shown to be quite accurate.
Collapse
Affiliation(s)
- R F Malenda
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - T J Price
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - J Stevens
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - S L Uppalapati
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - A Fragale
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - P M Weiser
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - A Kuczala
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| | - D Talbi
- Laboratoire Univers et Particules de Montpellier, UMR 5299, Université Montpellier, Place Eugène Bataillon, 34095 Montpellier, France
| | - A P Hickman
- Department of Physics, Lehigh University, 16 Memorial Dr. East, Bethlehem, Pennsylvania 18015, USA
| |
Collapse
|
10
|
Chadwick H, Brouard M, Perkins T, Aoiz F. Collisional depolarisation in electronically excited radicals. INT REV PHYS CHEM 2014. [DOI: 10.1080/0144235x.2014.891855] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
11
|
Chadwick H, Brouard M, Chang YP, Eyles CJ, McCrudden G, Perkins T, Seamons SA, Kłos J, Alexander MH, Dagdigian PJ, Herráez-Aguilar D, Aoiz FJ. The collisional depolarization of OH(A 2Σ+) and NO(A 2Σ+) with Kr. J Chem Phys 2014; 140:054306. [DOI: 10.1063/1.4863446] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
12
|
McGurk SJ, McKendrick KG, Costen ML, Alexander MH, Dagdigian PJ. Parity-dependent oscillations in collisional polarization transfer: CN(A²Π, v = 4) + Ar. J Chem Phys 2013; 139:124304. [PMID: 24089764 DOI: 10.1063/1.4821602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report the first systematic experimental and theoretical study of the state-to-state transfer of rotational angular momentum orientation in a (2)Π-rare gas system. CN(X(2)Σ(+)) was produced by pulsed 266 nm photolysis of ICN in a thermal bath (296 K) of Ar collider gas. A pulsed circularly polarized tunable dye laser prepared CN(A(2)Π, v = 4) in two fully state-selected initial levels, j = 6.5 F1e and j = 10.5 F2f, with a known laboratory-frame orientation. Both the prepared levels and a range of product levels, j' F1e and j' F2f, were monitored using the circular polarized output of a tunable diode laser via cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM Doppler lineshapes for co-rotating and counter-rotating pump-and-probe geometries reveal the time-dependence of the populations and orientations. Kinetic fitting was used to extract the state-to-state population transfer rate constants and orientation multipole transfer efficiencies (MTEs), which quantify the degree of conservation of initially prepared orientation in the product level. Complementary full quantum scattering (QS) calculations were carried out on recently computed ab initio potential energy surfaces. Collision-energy-dependent tensor cross sections for ranks K = 0 and 1 were computed for transitions from both initial levels to all final levels. These quantities were integrated over the thermal collision energy distribution to yield predictions of the experimentally observed state-to-state population transfer rate constants and MTEs. Excellent agreement between experiment and theory is observed for both measured quantities. Dramatic oscillations in the MTEs are observed, up to and including changes in the sign of the orientation, as a function of even/odd Δj within a particular spin-orbit and e/f manifold. These oscillations, along with those also observed in the state-to-state rate constants, reflect the rotational parity of the final level. In general, parity-conserving collisions conserve rotational orientation, while parity-changing collisions result in large changes in the orientation. The QS calculations show that the dynamics of the collisions leading to these different outcomes are fundamentally different. We propose that the origin of this behavior lies in interferences between collisions that sample the even and odd-λ terms in the angular expansions of the PESs.
Collapse
Affiliation(s)
- S J McGurk
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | | | | | | | | |
Collapse
|
13
|
Lehman JH, Lester MI, Kłos J, Alexander MH, Dagdigian PJ, Herráez-Aguilar D, Aoiz FJ, Brouard M, Chadwick H, Perkins T, Seamons SA. Electronic Quenching of OH A 2Σ+ Induced by Collisions with Kr Atoms. J Phys Chem A 2013; 117:13481-90. [DOI: 10.1021/jp407035p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Julia H. Lehman
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Marsha I. Lester
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | | | | | - Paul J. Dagdigian
- Department
of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, United States
| | - Diego Herráez-Aguilar
- Departamento
de Quimica Fisica, Facultad de Quimica, Universidad Complutense, Madrid 28040, Spain
| | - F. Javier Aoiz
- Departamento
de Quimica Fisica, Facultad de Quimica, Universidad Complutense, Madrid 28040, Spain
| | - Mark Brouard
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Helen Chadwick
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Tom Perkins
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Scott A. Seamons
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| |
Collapse
|
14
|
Dagdigian PJ. Theoretical investigation of collisional energy transfer in polyatomic intermediates. INT REV PHYS CHEM 2013. [DOI: 10.1080/0144235x.2012.758543] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
15
|
Chadwick H, Brouard M, Chang YP, Eyles CJ, Perkins T, Seamons SA, Kłos J, Alexander MH, Aoiz FJ. A new potential energy surface for OH(A 2Σ+)–Kr: The van der Waals complex and inelastic scattering. J Chem Phys 2012; 137:154305. [DOI: 10.1063/1.4757859] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
16
|
McGurk SJ, McKendrick KG, Costen ML, Bennett DIG, Kłos J, Alexander MH, Dagdigian PJ. Depolarization of rotational angular momentum in CN(A2Π, v = 4) + Ar collisions. J Chem Phys 2012; 136:164306. [PMID: 22559481 DOI: 10.1063/1.4705118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Angular momentum depolarization and population transfer in CN(A(2)Π, v = 4, j, F(1)e) + Ar collisions have been investigated both experimentally and theoretically. Ground-state CN(X(2)Σ(+)) molecules were generated by pulsed 266-nm laser photolysis of ICN in a thermal (nominally 298 K) bath of the Ar collision partner at a range of pressures. The translationally thermalized CN(X) radicals were optically pumped to selected unique CN(A(2)Π, v = 4, j = 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5, F(1)e) levels on the A-X (4,0) band by a pulsed tunable dye laser. The prepared level was monitored in a collinear geometry by cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM lineshapes for co- and counter-rotating circular pump and probe polarizations were analyzed to extract the time dependence of the population and (to a good approximation) orientation (tensor rank K = 1 polarization). The corresponding parallel and perpendicular linear polarizations yielded population and alignment (K = 2). The combined population and polarization measurements at each Ar pressure were fitted to a 3-level kinetic model, the minimum complexity necessary to reproduce the qualitative features of the data. Rate constants were extracted for the total loss of population and of elastic depolarization of ranks K = 1 and 2. Elastic depolarization is concluded to be a relatively minor process in this system. Complementary full quantum scattering (QS) calculations were carried out on the best previous and a new set of ab initio potential energy surfaces for CN(A)-Ar. Collision-energy-dependent elastic tensor and depolarization cross sections for ranks K = 1 and 2 were computed for CN(A(2)Π, v = 4, j = 1.5-10.5, F(1)e) rotational/fine-structure levels. In addition, integral cross sections for rotationally inelastic transitions out of these levels were computed and summed to yield total population transfer cross sections. These quantities were integrated over a thermal collision-energy distribution to yield the corresponding rate constants. A complete master-equation simulation using the QS results for the selected initial level j = 6.5 gave close, but not perfect, agreement with the near-exponential experimental population decays, and successfully reproduced the observed multimodal character of the polarization decays. On average, the QS population removal rate constants were consistently 10%-15% higher than those derived from the 3-level fit to the experimental data. The QS and experimental depolarization rate constants agree within the experimental uncertainties at low j, but the QS predictions decline more rapidly with j than the observations. In addition to providing a sensitive test of the achievable level of agreement between state-of-the art experiment and theory, these results highlight the importance of multiple collisions in contributing to phenomenological depolarization using any method sensitive to both polarized and unpolarized molecules in the observed level.
Collapse
Affiliation(s)
- S J McGurk
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
17
|
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]
|
18
|
Paterson G, Relf A, Costen ML, McKendrick KG, Alexander MH, Dagdigian PJ. Rotationally elastic and inelastic dynamics of NO(X2Π, v = 0) in collisions with Ar. J Chem Phys 2011; 135:234304. [PMID: 22191872 DOI: 10.1063/1.3665135] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A combined theoretical and experimental study of the depolarization of selected NO(X(2)Π, v = 0, j, F, ɛ) levels in collisions with a thermal bath of Ar has been carried out. Rate constants for elastic depolarization of rank K = 1 (orientation) and K = 2 (alignment) were extracted from collision-energy-dependent quantum scattering calculations, along with those for inelastic population transfer to discrete product levels. The rate constants for total loss of polarization of selected initial levels, which are the sum of elastic depolarization and population transfer contributions, were measured using a two-color polarization spectroscopy technique. Theory and experiment agree qualitatively that the rate constants for total loss of polarization decline modestly with j, but the absolute values differ by significantly more than the statistical uncertainties in the measurements. The reasons for this discrepancy are as yet unclear. The lack of a significant K dependence in the experimental data is, however, consistent with the theoretical prediction that elastic depolarization makes only a modest contribution to the total loss of polarization. This supports a previous conclusion that elastic depolarization for NO(X(2)Π) + Ar is significantly less efficient than for the electronically closely related system OH(X(2)Π) + Ar [P. J. Dagdigian and M. H. Alexander, J. Chem. Phys. 130, 204304 (2009)].
Collapse
Affiliation(s)
- G Paterson
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, United Kingdom
| | | | | | | | | | | |
Collapse
|
19
|
Paterson G, Costen ML, McKendrick KG. Collisional depolarization of rotational angular momentum: what are the observables and how can they be measured? Mol Phys 2011. [DOI: 10.1080/00268976.2011.621901] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
|
20
|
Brouard M, Chadwick H, Chang YP, Eyles CJ, Aoiz FJ, Kłos J. Collisional angular momentum depolarization of OH(A) and NO(A) by Ar: A comparison of mechanisms. J Chem Phys 2011; 135:084306. [DOI: 10.1063/1.3625638] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
21
|
Brouard M, Chadwick H, Eyles CJ, Aoiz FJ, Kłos J. The k-j-j′ vector correlation in inelastic and reactive scattering. J Chem Phys 2011; 135:084305. [DOI: 10.1063/1.3625637] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
22
|
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]
|
23
|
Lemeshko M, Friedrich B. Model Analysis of Rotationally Inelastic Ar + H2O Scattering in an Electric Field. J Phys Chem A 2009; 113:15055-63. [DOI: 10.1021/jp9051598] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mikhail Lemeshko
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Bretislav Friedrich
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
| |
Collapse
|
24
|
Costen ML, Livingstone R, McKendrick KG, Paterson G, Brouard M, Chadwick H, Chang YP, Eyles CJ, Aoiz FJ, Kłos J. Elastic Depolarization of OH(A) by He and Ar: A Comparative Study. J Phys Chem A 2009; 113:15156-70. [DOI: 10.1021/jp905348c] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | | | | | | | | | | | | | | | - F. J. Aoiz
- Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain
| | - J. Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
| |
Collapse
|
25
|
Dagdigian PJ, Alexander MH. Dependence of elastic depolarization cross sections on the potential: OH(X 2Pi)-Ar and NO(X 2Pi)-Ar. J Chem Phys 2009; 130:204304. [PMID: 19485446 DOI: 10.1063/1.3139522] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Elastic tensor and depolarization cross sections are computed for the collision of two exemplary diatomic molecules with (2)Pi electronic ground states-OH and NO-with argon. The interaction of a diatomic molecule in a Pi state with a spherical collision partner must be described by two potential energy surfaces (PESs), corresponding to the two asymptotically degenerate electronic states, of A(') and A(") symmetry. Quantum scattering calculations are most naturally based on the average (V(sum)) and half-difference (V(dif)) of these two PESs. When V(dif) is neglected, the OH(X (2)Pi)-Ar depolarization cross sections are found to be significantly reduced in magnitude, while the NO(X (2)Pi)-Ar cross sections are relatively unaffected. In addition, treating the molecules as closed-shell (1)Sigma(+) species with a corresponding rotational level structure and using (V(sum)) to model the PES, we predict depolarization cross sections which differ significantly from those based on full inclusion of the electronic degeneracy and fine structure of these (2)Pi molecules. This indicates that any single-PES-based simulation of the collisional depolarization of these two molecules would be subject to significant error.
Collapse
Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA.
| | | |
Collapse
|
26
|
Brouard M, Bryant A, Chang YP, Cireasa R, Eyles CJ, Green AM, Marinakis S, Aoiz FJ, Kłos J. Collisional depolarization of OH(A) with Ar: Experiment and theory. J Chem Phys 2009; 130:044306. [DOI: 10.1063/1.3061551] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
27
|
Paterson G, Marinakis S, Kłos J, Costen ML, McKendrick KG. Depolarisation of rotational orientation and alignment in OH (X2Π) + Xe collisions. Phys Chem Chem Phys 2009; 11:8804-12. [DOI: 10.1039/b909050a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
28
|
Brouard M, Chadwick H, Chang YP, Cireasa R, Eyles CJ, La Via AO, Screen N, Aoiz FJ, Kłos J. Collisional depolarization of NO(A) by He and Ar studied by quantum beat spectroscopy. J Chem Phys 2009. [DOI: 10.1063/1.3212608] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|