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Ma L, Dagdigian PJ, Alexander MH. Theoretical investigation of the relaxation of the bending mode of CH₂(X̃) by collisions with helium. J Chem Phys 2014; 141:214305. [PMID: 25481142 DOI: 10.1063/1.4902004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH2) in its X̃³B₁ state with He [L. Ma, P. J. Dagdigian, and M. H. Alexander, J. Chem. Phys. 136, 224306 (2012)]. By integration over products of the bending vibrational wave function, in a quantum close-coupled treatment we have calculated cross sections for the ro-vibrational relaxation of CH 2(X̃). Specifically, we find that cross sections for a loss of one vibrational quantum (v(b) = 2 → 1 and 1 → 0) are roughly two orders of magnitude smaller, and those for a loss of two vibrational quanta (v(b) = 2 → 0) four orders of magnitude smaller, than those for pure rotational relaxation. In addition, no clear cut dependence on the energy gap is seen.
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Affiliation(s)
- Lifang Ma
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
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Ma L, Alexander MH, Dagdigian PJ. Theoretical investigation of intersystem crossing between the ã¹A₁ and X³B₁ states of CH₂ induced by collisions with helium. J Chem Phys 2014; 141:064312. [PMID: 25134576 DOI: 10.1063/1.4892377] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Collisional energy transfer between the ground (X³B₁) and first excited (ã¹A₁) states of CH2 is facilitated by strong mixing of the rare pairs of accidentally degenerate rotational levels in the ground vibrational manifold of the [Formula: see text] state and the (020) and (030) excited bending vibrational manifolds of the X state. The simplest model for this process involves coherent mixing of the scattering T-matrix elements associated with collisional transitions within the unmixed ã and X states. From previous calculations in our group, we have determined cross sections and room-temperature rate constants for intersystem crossing of CH2 by collision with He. These are used in simulations of the time dependence of the energy flow, both within and between the X and ã vibronic manifolds. Relaxation proceeds through three steps: (a) rapid equilibration of the two mixed-pair levels, (b) fast relaxation within the ã state, and (c) slower relaxation among the levels of the X state. Collisional transfer between the fine-structure levels of the triplet (X) state is very slow.
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Affiliation(s)
- Lifang Ma
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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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]
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Dagdigian PJ, Alexander MH. Exact quantum scattering calculations of transport properties: CH2(X̃3B1, ã1A1)–helium. J Chem Phys 2013; 138:164305. [DOI: 10.1063/1.4801789] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Tscherbul TV, Grinev TA, Yu HG, Dalgarno A, Kłos J, Alexander MH. Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + CH 2(X̃) collisions. J Chem Phys 2012; 137:104302. [DOI: 10.1063/1.4748258] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Dagdigian PJ, Alexander MH. Theoretical investigation of rotationally inelastic collisions of CH2(X̃) with helium. J Chem Phys 2012; 136:224306. [DOI: 10.1063/1.4729050] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Chang CH, Xin J, Latsha T, Otruba E, Wang Z, Hall GE, Sears TJ, Chang BC. CH2 b̃1B1-ã1A1 band origin at 1.20 μm. J Phys Chem A 2011; 115:9440-6. [PMID: 21314141 DOI: 10.1021/jp1115965] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The origin band in the b̃(1)B(1)-ã(1)A(1) transition of CH(2) near 1.2 μm has been recorded at Doppler-limited resolution using diode laser transient absorption spectroscopy. The assignments of rotational transitions terminating in upper state levels with K(a) = 0 and 1, were confirmed by ground state combination differences and extensive optical-optical double resonance experiments. The assigned lines are embedded in a surprisingly dense spectral region, which includes a strong hot band, b̃(0,1,0) K(a) = 0 - ã(0,1,0) K(a) = 1 sub-band lines, with combination or overtone transitions in the ã(1)A(1) state likely responsible for the majority of unassigned transitions in this region. From measured line intensities and an estimate of the concentration of CH(2) in the sample, we find the transition moment square for the 0(00) ← 1(10) transition in the b̃(1)B(1)(0,0,0)(0)-ã(1)A(1)(0,0,0)(1) sub-band is 0.005(1) D(2). Prominent b̃(1)B(1)(0,1,0)(0)-ã(1)A(1)(0,1,0)(1) hot band lines were observed in the same spectral region. Comparison of the intensities of corresponding rotational transitions in the two bands suggests the hot band has an intrinsic strength approximately 28 times larger than the origin band. Perturbations of the excited state K(a) = 0 and 1 levels are observed and discussed. The new measurements will lead to improved future theoretical modeling and calculations of the Renner-Teller effect between the ã and b̃ states in CH(2).
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Affiliation(s)
- Chih-Hsuan Chang
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Ma L, Alexander MH, Dagdigian PJ. Theoretical investigation of rotationally inelastic collisions of CH2(ã) with helium. J Chem Phys 2011; 134:154307. [DOI: 10.1063/1.3575200] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Tscherbul TV, Yu HG, Dalgarno A. Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap. PHYSICAL REVIEW LETTERS 2011; 106:073201. [PMID: 21405515 DOI: 10.1103/physrevlett.106.073201] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Indexed: 05/30/2023]
Abstract
We present a rigorous theoretical study of low-temperature collisions of polyatomic molecular radicals with (1)S(0) atoms in the presence of an external magnetic field. Accurate quantum scattering calculations based on ab initio and scaled interaction potentials show that collision-induced spin relaxation of the prototypical organic molecule CH(2)(X(3)B(1)) (methylene) and nine other triatomic radicals in cold (3)He gas occurs at a slow rate, demonstrating that cryogenic buffer-gas cooling and magnetic trapping of these molecules is feasible with current technology. Our calculations further suggest that it may be possible to create ultracold gases of polyatomic molecules by sympathetic cooling with alkaline-earth atoms in a magnetic trap.
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Affiliation(s)
- T V Tscherbul
- Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, USA
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Chang CH, Hall GE, Sears TJ. Sub-Doppler spectroscopy of mixed state levels in CH(2). J Chem Phys 2010; 133:144310. [PMID: 20950003 DOI: 10.1063/1.3502084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Perturbations in the 7(16) and 8(18) mixed singlet/triplet levels of ã (1)A(1)(0,0,0) methylene, CH(2), have been reinvestigated by frequency-modulated laser sub-Doppler saturation spectroscopy. The hyperfine structure was completely resolved for both the predominantly singlet and the predominantly triplet components of these mixed rotational levels using b̃ (1)B(1)-ã (1)A(1) optical transitions near 12 200 cm(-1) with megahertz resolution. The mixing coefficients were obtained from the observed hyperfine splittings and a two-level deperturbation model. The analysis also determines the energy separation of the unperturbed zero-order levels and the unperturbed hyperfine splittings for the triplet perturbing levels 6(15) X̃ (3)B(1)(0,3,0) and 9(37) X̃ (3)B(1)(0,2,0).
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Affiliation(s)
- Chih-Hsuan Chang
- Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA
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Gannon KL, Blitz MA, Kovács T, Pilling MJ, Seakins PW. State resolved measurements of a (1)CH(2) removal confirm predictions of the gateway model for electronic quenching. J Chem Phys 2010; 132:024302. [PMID: 20095669 DOI: 10.1063/1.3263617] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Collisional quenching of electronically excited states by inert gases is a fundamental physical process. For reactive excited species such as singlet methylene, (1)CH(2), the competition between relaxation and reaction has important implications in practical systems such as combustion. The gateway model has previously been applied to the relaxation of (1)CH(2) by inert gases [U. Bley and F. Temps, J. Chem. Phys. 98, 1058 (1993)]. In this model, gateway states with mixed singlet and triplet character allow conversion between the two electronic states. The gateway model makes very specific predictions about the relative relaxation rates of ortho and para quantum states of methylene at low temperatures; relaxation from para gateway states leads to faster deactivation independent of the nature of the collision partner. Experimental data are reported here which for the first time confirm these predictions at low temperatures for helium. However, it was found that in contrast with the model predictions, the magnitude of the effect decreases with increasing size of the collision partner. It is proposed that the attractive potential energy surface for larger colliders allows alternative gateway states to contribute to relaxation removing the dominance of the para gateway states.
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Affiliation(s)
- K L Gannon
- School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom
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Pavlovic Z, Tscherbul TV, Sadeghpour HR, Groenenboom GC, Dalgarno A. Cold Collisions of OH(2Π) Molecules with He Atoms in External Fields. J Phys Chem A 2009; 113:14670-80. [DOI: 10.1021/jp904512r] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Z. Pavlovic
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, Department of Physics, University of Connecticut, Storrs, Connecticut 06269, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - T. V. Tscherbul
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, Department of Physics, University of Connecticut, Storrs, Connecticut 06269, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - H. R. Sadeghpour
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, Department of Physics, University of Connecticut, Storrs, Connecticut 06269, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - G. C. Groenenboom
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, Department of Physics, University of Connecticut, Storrs, Connecticut 06269, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - A. Dalgarno
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, Department of Physics, University of Connecticut, Storrs, Connecticut 06269, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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Dawes R, Wagner AF, Thompson DL. Ab Initio Wavenumber Accurate Spectroscopy: 1CH2 and HCN Vibrational Levels on Automatically Generated IMLS Potential Energy Surfaces. J Phys Chem A 2009; 113:4709-21. [DOI: 10.1021/jp900409r] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Richard Dawes
- Department of Chemistry, University of Missouri—Columbia, Columbia, Missouri 65211, and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
| | - Albert F. Wagner
- Department of Chemistry, University of Missouri—Columbia, Columbia, Missouri 65211, and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
| | - Donald L. Thompson
- Department of Chemistry, University of Missouri—Columbia, Columbia, Missouri 65211, and Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
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Sioutis I, Mishra S, Poluyanov LV, Domcke W. Renner-Teller and spin-orbit vibronic coupling effects in linear triatomic molecules with a half-filled π shell. J Chem Phys 2008; 128:124318. [DOI: 10.1063/1.2840356] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
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