Projection-reduced close coupling calculations of cross sections for vibrational relaxation in collisions of diatomic molecules with atoms

Buchachenko

Markovíc

et al. 2002

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The Boltzmann averaged rate constants for total vibrational relaxation of HF(vϭ1) in collisions with Ar are computed in the range of temperatures between 100 and 1500 K. The computed rate constants overestimate the experimental measurements at high temperatures by a large factor. It is concluded that the deviation between theory and experiment cannot be explained by inaccuracy of the PES or dynamical approximations made. It is shown that increasing initial rotational energy enhances a resonant character of the vibrational energy transfer to a great extent. An assumption is made that total vibrational relaxation of HF(vϭ1) at high temperatures is determined by competition between vibrational relaxation to a resonant level (vϭ0,j res), vibrational excitation from the resonant level, and purely rotational relaxation of HF(vϭ0,j res). It is demonstrated that at high temperatures the latter process can be significantly slower than vibrationally inelastic transitions and rotational relaxation of HF(vϭ0,j res) may in fact be a rate-limiting stage of vibrational relaxation.

Section: Resultsmentioning

confidence: 85%

Section: Computational Detailsmentioning

confidence: 90%

Resonance and reversibility of vibrational relaxation of HF in high temperature Ar bath gas

Buchachenko

Markovíc

et al. 2002

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“…The body-fixed projection of the total angular momentum ⍀ = + + k is conserved in the absence of the Coriolis interaction, and states with large values of ⍀ play no role for transitions involving low rotational angular momenta of the diatomic molecule. 1,74 We neglect states with ͉⍀͉ Ͼ 4 in our basis set and perform the calculations as explained in Ref. 74.…”

Section: Theorymentioning

confidence: 99%

“…1,74 We neglect states with ͉⍀͉ Ͼ 4 in our basis set and perform the calculations as explained in Ref. 74.…”

Section: Theorymentioning

confidence: 99%

Spin-orbit relaxation of Cl(P1∕22) and F(P1∕22) in a gas of H2

Abrahamsson

Groenenboom

2007

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The authors present quantum scattering calculations of rate coefficients for the spin-orbit relaxation of F͑ 2 P 1/2 ͒ atoms in a gas of H 2 molecules and Cl͑ 2 P 1/2 ͒ atoms in a gas of H 2 and D 2 molecules. Their calculation of the thermally averaged rate coefficient for the electronic relaxation of chlorine in H 2 agrees very well with an experimental measurement at room temperature. It is found that the spin-orbit relaxation of chlorine atoms in collisions with hydrogen molecules in the rotationally excited state j = 2 is dominated by the near-resonant electronic-to-rotational energy transfer accompanied by rotational excitation of the molecules. The rate of the spin-orbit relaxation in collisions with D 2 molecules increases to a great extent with the rotational excitation of the molecules. They have found that the H 2 /D 2 isotope effect in the relaxation of Cl͑ 2 P 1/2 ͒ is very sensitive to temperature due to the significant role of molecular rotations in the nonadiabatic transitions. Their calculation yields a rate ratio of 10 for the electronic relaxation in H 2 and D 2 at room temperature, in qualitative agreement with the experimental measurement of the isotope ratio of about 5. The isotope effect becomes less significant at higher temperatures.

“…The calculations at energies greater than 7 cm Ϫ1 were performed for 50 partial waves and the cross sections at energies greater than 1700 cm Ϫ1 were summed over 70 total angular momenta. Projection-reduced basis sets 22,39 were used for the computations with maximum value of ⍀ϭ4 allowed for all ro-electronic states. This procedure gives fully converged results.…”

Section: Resultsmentioning

confidence: 99%

Electronic and rotational energy transfer in F(2P1/2)+H2 collisions at ultracold temperatures

Dalgarno

2002

The dynamics of F( 2 P 1/2 )ϩH 2 scattering at ultracold temperatures is studied. It is shown that both the rotational and vibrational excitation of H 2 molecules decrease substantially the efficiency of spin-orbit relaxation in FϩH 2 collisions. It is observed that the near-resonant electronic transition leading to rotational excitation of H 2 ( jϭ0) is of the same magnitude at high energies as the off-resonant transition in which the rotational angular momentum of H 2 is preserved but becomes dominant in ultracold collisions. The zero temperature rate constant for spin-orbit relaxation of F is computed and suggestions are made as to the chemical reactivity of F( 2 P 1/2 ) atoms at ultracold temperatures. It is found that rotational relaxation of excited H 2 molecules is significantly enhanced by electronic transitions in F atoms and the electronic relaxation in F( 2 P 1/2 )ϩH 2 ( jϾ0) collisions is suppressed by rotational relaxation of H 2 .