1
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Davis JP, Neisser RW, Kidwell NM. Infrared Activated Signatures and Jahn-Teller Dynamics of NO-CH 4 Collision Complexes. J Phys Chem A 2023. [PMID: 37285367 DOI: 10.1021/acs.jpca.3c01410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Bimolecular collision outcomes sensitively depend on the chemical functionality and relative orientations of the colliding partners that define the accessible reactive and nonreactive pathways. Accurate predictions from multidimensional potential energy surfaces demand a full characterization of the available mechanisms. Therefore, there is a need for experimental benchmarks to control and characterize the collision conditions with spectroscopic accuracy to accelerate the predictive modeling of chemical reactivity. To this end, the bimolecular collision outcomes can be investigated systematically by preparing reactants in the entrance channel prior to reaction. Herein, we investigate the vibrational spectroscopy and infrared-driven dynamics of the bimolecular collision complex between nitric oxide and methane (NO-CH4). We recorded the vibrational spectroscopy of NO-CH4 in the CH4 asymmetric stretching region using resonant ion-depletion infrared spectroscopy and infrared action spectroscopy, thus revealing a significantly broad spectrum centered at 3030 cm-1 that extends over 50 cm-1. The asymmetric CH stretch feature of NO-CH4 is explained by CH4 internal rotation and attributed to transitions involving three different nuclear spin isomers of CH4. The vibrational spectra also show extensive homogeneous broadening due to the ultrafast vibrational predissociation of NO-CH4. Additionally, we combine infrared activation of NO-CH4 with velocity map imaging of NO (X2Π, ν″ = 0, J″, Fn, Λ) products to develop a molecular-level understanding of the nonreactive collisions of NO with CH4. The anisotropy of the ion image features is largely determined by the probed rotational quantum number of NO (J″) products. For a subset of NO fragments, the ion images and total kinetic energy release (TKER) distributions show an anisotropic component at low relative translation (∼225 cm-1) indicating a prompt dissociation mechanism. However, for other detected NO products, the ion images and TKER distributions are bimodal, in which the anisotropic component is accompanied by an isotropic feature at high relative translation (∼1400 cm-1) signifying a slow dissociation pathway. In addition to the predissociation dynamics following vibrational excitation, the Jahn-Teller dynamics prior to infrared activation need to be considered to fully describe the product spin-orbit distributions. Therefore, we correlate the Jahn-Teller mechanisms of NO-CH4 to the symmetry-restricted NO (X2Π, ν″ = 0, J″, Fn, Λ) + CH4 (ν″) product outcomes.
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Affiliation(s)
- John P Davis
- Department of Chemistry, The College of William & Mary, Williamsburg, Virginia 23187-8795, United States
| | - Ruby W Neisser
- Department of Chemistry, The College of William & Mary, Williamsburg, Virginia 23187-8795, United States
| | - Nathanael M Kidwell
- Department of Chemistry, The College of William & Mary, Williamsburg, Virginia 23187-8795, United States
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2
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Telfah H, Sharma K, Paul AC, Riyadh SMS, Miller TA, Liu J. A combined experimental and computational study on the transition of the calcium isopropoxide radical as a candidate for direct laser cooling. Phys Chem Chem Phys 2022; 24:8749-8762. [PMID: 35352070 DOI: 10.1039/d1cp04107j] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Vibronically resolved laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down (CRD) spectra of the electronic transition of the calcium isopropoxide [CaOCH(CH3)2] radical have been obtained under jet-cooled conditions. An essentially constant energy separation of 68 cm-1 has been observed for the vibrational ground levels and all fundamental vibrational levels accessed in the LIF measurement. To simulate the experimental spectra and assign the recorded vibronic bands, Franck-Condon (FC) factors and vibrational branching ratios (VBRs) are predicted from vibrational modes and their frequencies calculated using the complete-active-space self-consistent field (CASSCF) and equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) methods. Combined with the calculated electronic transition energy, the computational results, especially those from the EOM-CCSD calculations, reproduced the experimental spectra with considerable accuracy. The experimental and computational results suggest that the FC matrix for the studied electronic transition is largely diagonal, but transitions from the vibrationless levels of the à state to the X̃-state levels of the CCC bending (ν14 and ν15), CaO stretch (ν13), and CaOC asymmetric stretch (ν9 and ν11) modes also have considerable intensities. Transitions to low-frequency in-plane [ν17(a')] and out-of-plane [ν30(a'')] CaOC bending modes were observed in the experimental LIF/DF spectra, the latter being FC-forbidden but induced by the pseudo-Jahn-Teller (pJT) effect. Both bending modes are coupled to the CaOC asymmetric stretch mode via the Duschinsky rotation, as demonstrated in the DF spectra obtained by pumping non-origin vibronic transitions. The pJT interaction also induces transitions to the ground-state vibrational level of the ν10(a') mode, which has the CaOC bending character. Our combined experimental and computational results provide critical information for future direct laser cooling of the target molecule and other alkaline earth monoalkoxide radicals.
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Affiliation(s)
- Hamzeh Telfah
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
| | - Ketan Sharma
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Anam C Paul
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
| | - S M Shah Riyadh
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40292, USA
| | - Terry A Miller
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA. .,Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40292, USA
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3
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Shen Y, Yarkony DR. Unified Description of the Jahn-Teller Effect in Molecules with Only C s Symmetry: Cyclohexoxy in Its Full 48-Dimensional Internal Coordinates. J Phys Chem A 2021; 126:61-67. [PMID: 34965116 DOI: 10.1021/acs.jpca.1c09123] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The two lowest potential energy surfaces of cyclohexoxy which are coupled by conical intersections and the spin-orbit interaction are determined in the full 48-dimensional internal coordinate space using a feedforward neural network to fit a diabatic potential energy matrix. The electronic structure data are obtained at the multireference configuration interaction with single- and double-excitation level. Underlying parallels between these coupled surfaces and those of the alkoxy radicals methoxy and isopropoxy are established. Earlier work by Dillon and Yarkony is extended. While the parallels would have been challenging to appreciate using the concept of the Jahn-Teller active modes, they are readily seen in terms of two internal modes centered at the conical intersection: g the energy difference gradient vector and h the interstate coupling gradient vector. In other words, g and h vectors provide a unified description of the Jahn-Teller effect in molecules exhibiting C3v and quasi-C3v symmetries. A spectral simulation in the full 48-vibrational-internal coordinate space is reported. This spectrum is obtained using recently developed algorithms designed to increase the size of the systems that can be treated with a time-independent vibronic coupling approach.
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Affiliation(s)
- Yifan Shen
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David R Yarkony
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
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4
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Paul AC, Sharma K, Telfah H, Miller TA, Liu J. Electronic spectroscopy of the A 1̃ 2A ''/A 2̃ 2A '-X̃ 2A ' transitions of jet-cooled calcium ethoxide radicals: Vibronic structure of alkaline earth monoalkoxide radicals of C s symmetry. J Chem Phys 2021; 155:024301. [PMID: 34266255 DOI: 10.1063/5.0056550] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down spectra of the A1̃2A''/A2̃2A'-X̃2A' electronic transition of the calcium ethoxide (CaOC2H5) radical have been obtained under jet-cooled conditions. An essentially constant Ã2-Ã1 energy separation for different vibronic levels is observed in the LIF spectrum, which is attributed to both the spin-orbit (SO) interaction and non-relativistic effects. Electronic transition energies, vibrational frequencies, and spin-vibrational eigenfunctions calculated using the coupled-cluster method, along with results from previous complete active space self-consistent field calculations, have been used to predict the vibronic energy level structure and simulate the recorded LIF/DF spectra. Although the vibrational frequencies and Franck-Condon (FC) factors calculated under the Born-Oppenheimer approximation and the harmonic oscillator approximation reproduce the dominant spectral features well, the inclusion of the pseudo-Jahn-Teller (pJT) and SO interactions, especially those between the A1̃2A″/A2̃2A' and the B̃2A' states, induces additional vibronic transitions and significantly improves the accuracy of the spectral simulations. Notably, the spin-vibronic interactions couple vibronic levels and alter transition intensities. The calculated FC matrix for the A1̃2A''/A2̃2A'-X̃2A' transition contains a number of off-diagonal matrix elements that connect the vibrational ground levels to the levels of the ν8 (CO stretch), ν11 (OCC bending), ν12 (CaO stretch), ν13 (in-plane CaOC bending), and ν21 (out-of-plane CaOC bending) modes, which are used for vibrational assignments. Transitions to the ν21(a″) levels are allowed due to the pJT effect. Furthermore, when LIF transitions to the Ã-state levels of the CaOC-bending modes, ν13 and ν21, are pumped, A1̃2A''/A2̃2A'→X̃2A' transitions to the combination levels of these two modes with the ν8, ν11, and ν12 modes are also observed in the DF spectra due to the Duschinsky mixing. Implications of the present spectroscopic investigation to laser cooling of asymmetric-top molecules are discussed.
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Affiliation(s)
- Anam C Paul
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA
| | - Ketan Sharma
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Hamzeh Telfah
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA
| | - Terry A Miller
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA
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5
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Dickerson CE, Guo H, Shin AJ, Augenbraun BL, Caram JR, Campbell WC, Alexandrova AN. Franck-Condon Tuning of Optical Cycling Centers by Organic Functionalization. PHYSICAL REVIEW LETTERS 2021; 126:123002. [PMID: 33834801 DOI: 10.1103/physrevlett.126.123002] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 02/24/2021] [Indexed: 06/12/2023]
Abstract
Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to large, organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wave function mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron-withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.
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Affiliation(s)
- Claire E Dickerson
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, USA
| | - Han Guo
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, USA
| | - Ashley J Shin
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, USA
| | | | - Justin R Caram
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, USA
| | - Wesley C Campbell
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, USA
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6
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Liu J, Miller TA. Laser-Induced Fluorescence Spectroscopy of Large Secondary Alkoxy Radicals: Part I. Spectral Overviews and Vibronic Analysis. J Phys Chem A 2021; 125:1391-1401. [PMID: 33565880 DOI: 10.1021/acs.jpca.0c10662] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report vibronically resolved laser-induced fluorescence (LIF) spectra of jet-cooled C5-C10 secondary alkoxy radicals. The LIF spectra demonstrate vibronic structures similar to smaller (C3-C4) secondary alkoxies. For 2-pentoxy and 2-hexoxy, rotationally resolved LIF spectra have also been recorded. Two types of rotational structures have been observed in vibronic bands of each molecule. Extensive quantum chemistry calculations have been performed on 2-pentoxy and 2-hexoxy. The computed results include the relative energies of conformers, their geometries, and the energy separations between the nearly degenerate à and X̃ electronic states (ΔEÃ-X̃). Based on the similarity between the vibronic structures of different secondary alkoxies and calculated molecular parameters, including the relative energies of conformers, the B̃ ← X̃ transition frequencies, and the vibrational frequencies, strong vibronic bands in the LIF spectra are assigned to the origin bands and CO stretch bands of the two lowest-energy conformers of each secondary alkoxy radical. The distinct rotational structures of the two different conformations of 2-pentoxy and 2-hexoxy will be simulated and analyzed in Part II of this series ( J. Phys. Chem. A 2021, DOI: 10.1021/acs.jpca.0c10663).
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Affiliation(s)
- Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States.,Department of Physics, University of Louisville, Louisville, Kentucky 40292, United States
| | - Terry A Miller
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States
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7
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Liu J, Chen MW, Miller TA. Laser-Induced Fluorescence Spectroscopy of Large Secondary Alkoxy Radicals: Part II. Rotational and Fine Structure. J Phys Chem A 2021; 125:1402-1412. [PMID: 33565876 DOI: 10.1021/acs.jpca.0c10663] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Selected vibronic bands of the B̃ ← X̃ laser-induced fluorescence (LIF) spectra of jet-cooled 2-pentoxy and 2-hexoxy, including the origin and CO-stretch bands, have been measured with rotational resolution and analyzed using (1) an effective Hamiltonian that comprises a rotational part and a spin-rotation (SR) part (the "isolated-states model") and (2) a recently developed Hamiltonian in which the nearly degenerate à and X̃ states are treated together (the "coupled-states model") (see Liu, J., J. Chem. Phys. 2018, 148, 124112). The observed rotational and fine structures of the strongest vibronic bands have first been simulated using a genetic algorithm with the isolated-states model. The parameters for the simulation include rotational constants for both the X̃ and B̃ states, which can be calculated from the electronic structure theory, as well as the electronic SR constants of the X̃ state and the transition dipole moments (TDMs), both of which are predicted based on their transferability in an "orbital-fixed coordinate system" using iso-propoxy as the reference molecule. Quantum chemistry calculations suggest that the lowest two electronic (X̃ and Ã) states of secondary alkoxy radicals have small energy separations on the order of 100 cm-1 (see Part I of this series: J. Phys. Chem. A 2021, DOI: 10.1021/acs.jpca.0c10662). The electron configurations of these two nearly degenerate states have been determined by comparing the experimentally determined rotational constants and the TDMs to the ones predicted for the X̃ and à states. The experimental LIF spectra were also simulated with the coupled-states model, in which the effective spin-orbit (SO) constants (aζed) and the SO-free separation between the à and the X̃ states (ΔE0) have been determined. Molecular constants derived from fitting the rotational and fine structures of the experimental LIF spectra enabled unambiguous assignment of the observed vibronic bands to specific conformers of 2-pentoxy and 2-hexoxy as reported in Part I.
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Affiliation(s)
- Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States.,Department of Physics, University of Louisville, Louisville, Kentucky 40292, United States
| | - Ming-Wei Chen
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Terry A Miller
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States
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8
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Yan Y, Sharma K, Miller TA, Liu J. Rotational and fine structure of open-shell molecules in nearly degenerate electronic states. II. Interpretation of experimentally determined interstate coupling parameters of alkoxy radicals. J Chem Phys 2020; 153:174306. [PMID: 33167646 DOI: 10.1063/5.0026212] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Rotationally and fine-structure resolved B̃←X̃ laser-induced fluorescence (LIF) spectra of alkoxy radicals have been simulated with a "coupled two-states model" [J. Liu, J. Chem. Phys. 148, 124112 (2018)], in which the nearly degenerate X̃ and à states are considered together. These two electronic states are separated by the "difference potential" and coupled by the spin-orbit (SO) interaction and the Coriolis interaction. Molecular constants determined in fitting the LIF spectra using the coupled two-states model provide quantitative insight into the SO and Coriolis interactions, as well as other intramolecular dynamics, including the pseudo-Jahn-Teller effect. The spectroscopic model also allows semi-quantitative prediction of effective spin-rotation constants using molecular geometry and SO constants, which can be calculated ab initio with considerable accuracy. The dependence of fit values of molecular constants on the size and conformation of alkoxy radicals is discussed.
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Affiliation(s)
- Yi Yan
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Ketan Sharma
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Terry A Miller
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
| | - Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA
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9
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Koncz B, Bazsó G, Reza MA, Telfah H, Hegedüs K, Liu J, Tarczay G. Revealing Long-Range Substituent Effects in the Laser-Induced Fluorescence and Dispersed Fluorescence Spectra of Jet-Cooled CH xF 3-xCH 2O ( x = 1, 2, 3) Radicals. J Phys Chem A 2019; 123:10947-10960. [PMID: 31790245 DOI: 10.1021/acs.jpca.9b09829] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The B̃-X̃ laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the atmospherically important β-monofluoro ethoxy (MFEO), β,β-difluoro ethoxy (DFEO), and β,β,β-trifluoro ethoxy (TFEO) radicals were recorded with vibronic resolution under jet-cooled conditions. To simulate the spectra, Franck-Condon factors were obtained from quantum chemical computations carried out at the CAM-B3LYP/6-311++G(d,p) level of theory. The simulations reproduce well both the LIF and DF spectra. Both conformers (G and T) of MFEO and one (G) of the two conformers of DFEO contribute to the LIF spectrum. A comparison between the experimental and calculated spectra confirms the expected long-range field effects of the CHxF3-x group on electronic transition energies and bond strengths, especially in the excited electronic (B̃) state. Although TFEO has only one conformer, its LIF spectrum is highly congested, which is attributed to the interaction between CO stretch and the -CF3 internal rotation.
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Affiliation(s)
- Benedek Koncz
- ELTE Eötvös University , Institute of Chemistry, Laboratory of Molecular Spectroscopy , PO Box 32, H-1518 Budapest 112 , Hungary
| | - Gábor Bazsó
- ELTE Eötvös University , Institute of Chemistry, Laboratory of Molecular Spectroscopy , PO Box 32, H-1518 Budapest 112 , Hungary
| | - Md Asmaul Reza
- Department of Chemistry , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States
| | - Hamzeh Telfah
- Department of Chemistry , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States
| | - Kristóf Hegedüs
- Research Centre for Natural Sciences , Institute of Organic Chemistry , PO Box 286, H-1519 Budapest , Hungary
| | - Jinjun Liu
- Department of Chemistry , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States.,Conn Center for Renewable Energy Research , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States
| | - György Tarczay
- ELTE Eötvös University , Institute of Chemistry, Laboratory of Molecular Spectroscopy , PO Box 32, H-1518 Budapest 112 , Hungary.,MTA-ELTE Lendület Laboratory Astrochemistry Research Group , PO Box 32, H-1518 Budapest 112 , Hungary
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10
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Liu J. Rotational and fine structure of open-shell molecules in nearly degenerate electronic states. J Chem Phys 2018; 148:124112. [DOI: 10.1063/1.5021946] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jinjun Liu
- Department of Chemistry, University of Louisville, 2320 S. Brook St., Louisville, Kentucky 40292, USA
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11
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Weichman ML, Cheng L, Kim JB, Stanton JF, Neumark DM. Low-lying vibronic level structure of the ground state of the methoxy radical: Slow electron velocity-map imaging (SEVI) spectra and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations. J Chem Phys 2017; 146:224309. [DOI: 10.1063/1.4984963] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Marissa L. Weichman
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Lan Cheng
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21208, USA
| | - Jongjin B. Kim
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - John F. Stanton
- Quantum Theory Project, Department of Chemistry and Physics, University of Florida, Gainesville, Florida 32611, USA
| | - Daniel M. Neumark
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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12
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Reza MA, Paul AC, Reilly NJ, Alam J, Liu J. Dispersed Fluorescence Spectroscopy of Jet-Cooled Isobutoxy and 2-Methyl-1-butoxy Radicals. J Phys Chem A 2016; 120:6761-7. [PMID: 27504673 DOI: 10.1021/acs.jpca.6b06445] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report dispersed fluorescence (DF) spectra of the isobutoxy and 2-methyl-1-butoxy radicals produced by photolysis of corresponding nitrites in supersonic jet expansion. Different vibrational structures have been observed in the DF spectra when different vibronic bands in the laser-induced fluorescence (LIF) spectra of each radical were pumped, which suggests that those vibronic bands be assigned to different conformers. Spectra simulated using calculated vibrational frequencies and Franck-Condon factors well reproduce the experimentally observed ones and support the assignment of the vibronic bands in the LIF spectra to the two lowest-energy conformers of each radical. DF spectra obtained by pumping the B̃ ← X̃ origin bands of the LIF spectra are dominated by CO stretch progressions because of the large difference in CO bond length between the ground (X̃) and the second excited (B̃) electronic states. Furthermore, with non-CO stretch bands pumped, the DF spectra are dominated by progressions of combination bands of the CO stretch and the pumped modes as a result of Duschinsky mixing. Ã-X̃ separation of both conformers of the isobutoxy radical has also been determined in the experiment.
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Affiliation(s)
- Md Asmaul Reza
- Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville , Louisville, Kentucky 40292, United States
| | - Anam C Paul
- Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville , Louisville, Kentucky 40292, United States
| | - Neil J Reilly
- Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville , Louisville, Kentucky 40292, United States
| | - Jahangir Alam
- Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville , Louisville, Kentucky 40292, United States
| | - Jinjun Liu
- Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville , Louisville, Kentucky 40292, United States
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13
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Liu J, Reilly NJ, Mason A, Miller TA. Laser-Induced Fluorescence Spectroscopy of Jet-Cooled t-Butoxy. J Phys Chem A 2015; 119:11804-12. [DOI: 10.1021/acs.jpca.5b08922] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | | | | | - Terry A. Miller
- Laser
Spectroscopy Facility, Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, Ohio 43210, United States
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14
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Alam J, Reza MA, Mason A, Reilly NJ, Liu J. Dispersed Fluorescence Spectroscopy of Jet-Cooled 2-, 3-, and 4-Methylcyclohexoxy Radicals. J Phys Chem A 2015; 119:6257-68. [PMID: 26016956 DOI: 10.1021/acs.jpca.5b03454] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Vibrational structures of the nearly degenerate X̃ and à states of the 2-, 3-, and 4-methylcyclohexoxy (MCHO) radicals were studied by jet-cooled dispersed fluorescence (DF) spectroscopy. The observed transitions were assigned on the basis of vibrational frequencies and Franck-Condon factors predicted by quantum chemical calculations. Intensities of vibronic transitions in the DF spectra are dependent on the laser-induced fluorescence (LIF) bands pumped in the experiment, which can be explained by the difference in geometry and symmetry between the lower X̃/à states and the highly excited B̃ state. All three studied isomers of MCHO have close-lying X̃ and à states although their energy separations are affected by the position of the methyl group. It is suggested by quantum chemical calculations that the lowest-energy conformers of all three isomers have the half-filled orbital oriented perpendicular to the OCH plane, which is consistent with the observed relative intensities of the B̃ → X̃ and B̃ → à origin bands. When the origin and the CO-stretch bands of the B̃ ← X̃ LIF excitation spectra were pumped, the DF spectra were dominated by CO-stretch progressions. When non-CO-stretch vibrational levels of the B̃ state were pumped, progressions of CO-stretch modes combined with the pumped vibrational mode were observed. Excited-state vibrational population relaxation from the CO stretch level to the vibrational ground level and from combination levels of the CO stretch mode and other vibrational modes to the non-CO stretch modes was observed. Analysis of the DF spectra confirms the previous conclusion that all strong LIF bands observed under jet-cooled conditions belong to a single conformer of each positional isomer (Lin et al. RSC Adv. 2012, 2, 583-589).
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Affiliation(s)
- Jahangir Alam
- †Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States
| | - Md Asmaul Reza
- †Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States
| | - Amy Mason
- †Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States
| | - Neil J Reilly
- †Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States
| | - Jinjun Liu
- †Department of Chemistry and ‡Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States
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15
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Hao H, Wang L, Zu L. Methyl substitution effect on the jet-cooled laser-induced fluorescence spectrum of cyclohexoxy radical. J Phys Chem A 2015; 119:3384-92. [PMID: 25781354 DOI: 10.1021/acs.jpca.5b00928] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the structure and properties of cyclohexoxy radical and its substitutes is important because of their presence in combustion processes, in atmospheric chemistry, and as intermediates in the hydrocarbon reactions. In this work, jet-cooled laser-induced fluorescence (LIF) spectra of five dimethyl substituted cyclohexoxy radicals are obtained for the first time. The correlation between the spectral variations and the radical structural changes is studied with the assistance of theoretical calculations at the B3LYP/6-31+G(d) and CASSCF/6-31+G(d) levels. The results show that the spectral characters of the dimethylcyclohexoxy radicals and their dissociation kinetics are predominantly affected by the methyl substitution position related to the C-O group. The spectral effect of the two methyl groups will add up if they locate on asymmetric carbons of the cyclohexoxy ring. Methyl substitution on β carbon weakens the six-member ring of cyclohexoxy and results in unimolecular dissociation via β C-C bond cleavage on the methyl group side and forms vinoxy variants. This study clearly shows that the LIF spectra can be used to identify cyclohexoxy and the isomers of its methyl substitutes. The results will help to understand the photochemistry of cyclic hydrocarbons in the atmospheric and combustion processes.
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Affiliation(s)
- Haiyan Hao
- College of Chemistry, Beijing Normal University, Beijing, 100875, People's Republic of China
| | - Lingxuan Wang
- College of Chemistry, Beijing Normal University, Beijing, 100875, People's Republic of China
| | - Lily Zu
- College of Chemistry, Beijing Normal University, Beijing, 100875, People's Republic of China
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Chhantyal-Pun R, Roudjane M, Melnik DG, Miller TA, Liu J. Jet-cooled laser-induced fluorescence spectroscopy of isopropoxy radical: vibronic analysis of B̃-X̃ and B̃-Ã band systems. J Phys Chem A 2014; 118:11852-70. [PMID: 25054866 DOI: 10.1021/jp504322j] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recently we published [ Liu et al. J. Chem. Phys. 2013 , 139 , 154312 ] an analysis of the rotational structure of the B̃-X̃ origin band spectrum of isopropoxy, which confirmed that the double methyl substitution of methoxy to yield the isopropoxy radical only slightly lifted the degeneracy of the former's X̃(2)E state. Additionally the spectral results provided considerable insight into the relativistic and nonrelativistic contributions to the experimental splitting between the components of the (2)E state. However, left unexplained was how the Jahn-Teller (JT) vibronic coupling terms within methoxy's (2)E state manifest themselves as pseudo-Jahn-Teller (pJT) vibronic coupling between the Ã(2)A″ and X̃(2)A' levels of isopropoxy. To cast additional light on this subject we have obtained new isopropoxy spectra and assigned a number of weak, "forbidden" vibronic transitions in the B̃-X̃ spectrum using new electronic structure calculations and rotational contour analyses. The mechanisms that provide the nonzero probability for these transitions shed considerable information on pJT, spin-orbit, and Coriolis coupling between the à and X̃ states. We also report a novel mechanism caused by pJT coupling that yields excitation probability to the B̃ state dependent upon the permanent dipole moments in the B̃ and à or X̃ states. By combining a new B̃-à and the earlier B̃-X̃ rotational analyses we determine a much improved value for the experimental Ã-X̃ separation.
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Affiliation(s)
- Rabi Chhantyal-Pun
- Laser Spectroscopy Facility, Department of Chemistry and Biochemistry, The Ohio State University , 120 West 18th Avenue, Columbus, Ohio 43210, United States
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