Energy Transfer in Near-Resonant Molecular Collisions due to Long-Range Forces with Application to Transfer of Vibrational Energy from ν3 Mode of CO2 to N2

Abstract

The cross section for the near-resonant transfer of vibrational energy from CO2(001) to N2(0), CO2(001) + N2(0)→CO2(000) + N2(1) + ΔE, is calculated for the isotopes N214 (ΔE = 18 cm−1) and N215 (ΔE = 97 cm−1). The impact parameter (semi-classical) approximation is used, and it is assumed that the vibrational-energy transfer is caused by the interaction of the instantaneous CO2 dipole moment with the N2 quadrupole moment. When proper account is taken of the rotational motions of the molecules it is found that in collisions of CO2 with 14N2 only the low rotational levels of the CO2 and N2 molecules contribute to Reaction (1). In collisions of CO2 with 15N2, only those rotational levels contribute which undergo transitions cancelling most of the relatively large (97 cm−1) vibrational-resonance defect. For 14N2 below about 1000°K, where the cross section displays a negative temperature dependence, the results are in excellent qualitative and quantitative agreement with available experimental data, with no adjustable parameters in the theory. Above about 1000°K the experimental cross-section data display a positive temperature dependence indicating that some other mechanism becomes important there. For 15N2 the calculations are in good agreement with an experimental measurement at 300°K. Data at other temperatures are not presently available. The theoretical results indicate that the cross section for the vibrational-energy transfer should have maximum around 200°K. Below this temperature the higher rotational levels which dominate the energy-transfer process are unfavorably weighted in the Boltzmann distribution.

Near-resonant energy transfer from highly vibrationally excited OH to N2

“…In other words, only up to about 25 cm −1 energy match may be efficiently transferred from internal degrees of freedom to translation. The rotational transitions that accompany the vibrational transitions therefore play a very important part in this theory 3,15 by increasing or decreasing the energy mismatch and dramatically decreasing or increasing P͑T͒. Further, P͑T͒ in most cases decreases with increasing T. In short, the approach taken in this paper has little in common with the calculation of Shalashilin et al…”

“…3 The good agreement between the calculated 3 and experimental 5 values leaves no room for ambiguity.…”

“…A measure of the energy that can be efficiently transferred from the internal degrees of freedom ͑vibration and rotation͒ to translational motion is given by the resonance function. A plot of the resonance function versus energy mismatch ͑absolute value of the difference in the energies in the internal degrees of freedom of the final and initial states͒ shows 3,15 that for thermal collisions, this function decays very rapidly for energy mismatch greater than about 25 cm −1 . In other words, only up to about 25 cm −1 energy match may be efficiently transferred from internal degrees of freedom to translation.…”

“…3 The fraction of vibrational energy of nascent OH transferred to N 2 and then eventually to CO 2 is rather small and does not impact the energy budget of the mesosphere. It does, however, severely impact the determination of the night-time volume mixing ratio of CO 2 in the mesosphere and thermosphere.…”

“…The hydroxyl radical OH is produced in the nocturnal terrestrial mesosphere by the reaction of H and O 3 and is formed mainly in high vibrational levels ͑7 ഛ ഛ 9͒, the fractional population of the nascent OH in levels 7, 8, and 9 being 0.15, 0.34, and 0.47, respectively.…”