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

Abstract

The probability per collision P͑T͒ of near-resonant vibration-to-vibration energy transfer ͑ET͒ of one quantum of vibrational energy from vibrational levels = 8 and = 9 of OH to N 2 ͑ =0͒, OH͑͒ +N 2 ͑0͒ → OH͑ −1͒ +N 2 ͑1͒, is calculated in the 100-350 K temperature range. These processes represent important steps in a model that explains the enhanced 4.3 m emission from CO 2 in the nocturnal mesosphere. The calculated energy transfer is mediated by weak long-range dipole-quadrupole interaction. The results of this calculation are very sensitive to the strength of the two transition moments. Because of the long range of the intermolecular potential, the resonance function, a measure of energy that can be efficiently exchanged between translation and vibration-rotation degrees of freedom, is rather narrow. A narrow resonance function coupled with the large rotational constant of OH is shown to render the results of the calculation very sensitive to the rotational distribution, or the rotational temperature if one exists, of this molecule. The calculations are carried out in the first and second orders of perturbation theory with the latter shown to give ET probabilities that are an order of magnitude larger than the former. The reasons for the difference in magnitude and temperature dependence of the first-and second-order calculations are discussed. The results of the calculations are compared with room temperature measurements as well as with an earlier calculation. Our calculated results are in good agreement with the room temperature measurements for the transfer of vibrational energy for the exothermic OH͑ =9͒ ET process but are about an order lower than the room temperature measurements for the exothermic OH͑ =8͒ ET process. The cause of this discrepancy is explored. This calculation does not give the large values of the rate coefficients needed by the model that explains the enhanced 4.3 m emission from CO 2 in the nocturnal mesosphere.

Collisional removal of OH(X2Π,υ= 9) by O, O2, O3, N2, and CO2

“…Using two different potential energy surfaces, Shalashilin et al [1992] obtained values of 4.91 × 10 −13 cm 3 s −1 and 1.10 × 10 −12 cm 3 s −1 for the rate constant of the OH( υ = 9) + N 2 vibrational‐to‐vibrational energy exchange at room temperature. Burtt and Sharma [2008b] performed calculations employing second order perturbation theory and a standard dipole moment function. Both studies show relatively good agreement at room temperature.…”

“…Both studies show relatively good agreement at room temperature. Nevertheless, they predict a different temperature dependence; Shalashilin et al [1992] found that the rate constant decreases with increasing temperature, whereas Burtt and Sharma [2008b] predict an increase with increasing temperature. Future experiments should clarify which theoretical approach is the most predictive for this process.…”

Model results of OH airglow considering four different wavelength regions to derive night-time atomic oxygen and atomic hydrogen in the mesopause region

“…They further exclude the sudden death mechanism as a possible deactivation scheme. There are also two theoretical studies (Shalashilin et al, 1995;Caridade et al, 2002) which investigated OH(ν) deactivation via O 2 , both supporting a combination of multiquantum and single-quantum quenching similar to the model of Adler-Golden (1997).…”

Vibrational energy transfer in O2(v=2–8)–O2(v=) collisions

“…In earlier calculations 40,41 involving high vibrational levels of OH the authors postulated an increase in the gas kinetic diameter and hard sphere diameter with vibrational quantum number. This was necessitated by dramatic change in the rotational constant of OH and hence the bond distance with vibrational quantum number ͑rotational constant changes 42 from 17.84 cm −1 for v = 1 to 12.92 cm −1 for v =8͒.…”