Dynamics Study of the O + HO₂ Reaction Using Two DMBE Potential Energy Surfaces:  The Role of Vibrational Excitation

Abstract

We investigate the effect of vibrational excitation on the dynamics and kinetics of the atmospheric reaction O( 3 P) + HO 2 f OH + O 2 using two double many-body expansion potential energy surfaces previously reported. The results show that such an effect is relatively minor even considering HO 2 with contents of vibrational excitation close to the H + O 2 dissociation asymptote. It should therefore not bear drastic implications in atmospheric modeling where such an effect has been ignored thus far.

Dynamics and kinetics of the S + HO2 reaction: A theoretical study

“…Meanwhile, the OH bond remains almost as a spectator, keeping its ro-vibrational distribution as originally was in HO 2 . Similar results have been observed for the reaction O + HO 2 when O 2 is formed [22] with a high rotational temperature.…”

What are the Implications of Nonequilibrium in the O+OH and O+HO2 Reactions?

“…As for the O + OH reaction, the strong correlation between the parameters suggests that their physical significance should be seen with caution. Also shown for comparison in Figure 10 are the results calculated for a vibrational energy of HO 2 equal to the ZPE, [93] as well as the available experimental measurements [94][95][96][97][98][99][100][101][102] and the recommended [81] value of k 7 (T) = 2.7 10 À11 exp(224/T) cm 3 s À1 which is valid over the temperature range 200 T/K 400. The significant result is that k 7 (T) is inhibited by vibrationally exciting HO 2 when compared with the case [93] where HO 2 is initially in the ground vibrational state, although its magnitude still fits within the error bars of the recommended [81] rate constant (except, perhaps, at low temperatures).…”

“…For example, at T = 255 K, such a decrease is 44 % for DMBE I and 36 % for DMBE II. This may be rationalized from the fact that, for a fixed vibrational excitation [93] of HO 2 , the rate constant increases slightly more in the case of DMBE II than in the case of DMBE I. However, such a discrepancy diminishes when considering the LTD micropopulation for HO 2 , since there is a high fraction of HO * 2 species that reacts via other channels.…”

Implications of the O + OH reaction in hydroxyl nightglow modeling

“…For example, although it has been noted (AdlerGolden, 1997) that the reaction O + HO 2 could be a potential candidate, previous work (Kaye, 1988) has shown that it is unlikely to play a crucial role in studies of the high atmosphere. Although this assumption is possibly valid for HO 2 in the ground vibrational state as the dynamics only yields OH(v ≤ 6), the argument no longer holds if non-LTE is considered, since up to OH(v = 15) products can then be formed (Silveira et al, 2004;Varandas, 2005b). In addition, the reaction of OH + O 3 has been shown to yield HO 2 vibrationally excited above the classical asymptote for dissociation, and thus can be another potential source of OH(v ) Zhang and Varandas, 2001).…”

“…When non-LTE conditions hold, the chemistry changes dramatically due to the differences in the internal energy content of the species involved: endothermic reactions become exothermic with rate constants substantially larger, at times orders of magnitude larger (Silveira et al, 2004;Varandas, 2005b). Although several studies have been devoted to the role of vibrationally excited species in reactions, particularly for the HO x cycle, atmospheric chemistry models of the middle-upper atmosphere neglect non-LTE (see, e.g., von Clarmann et al, 2010 and references therein).…”