Dynamics Study of the O₂ + HO₂ Atmospheric Reaction with Both Reactants Highly Vibrationally Excited

Abstract

We report a theoretical study of the title five-atom atmospheric reaction for vibrationally excited states of O 2 over the range 18 e V e 27, and initial vibrational energies of HO 2 over the range 36 e E V /kcalmol -1 e 51. All calculations have employed the quasiclassical trajectory method and the realistic double many-body expansion potential energy surface recently reported for HO 4 ( 2 A). The results indicate that it can be a potential source of ozone in the upper atmosphere.

Vibrational relaxation of highly excited HO2 in collisions with O2

“…The deactivation cross-sections show a markedly decreasing pattern with translational energy, suggesting that a capture-like mechanism arising from the strong coupling of the available degrees of freedom governed by the long range interactions dominates over the whole range of translational energies. Such a behavior is quite similar to the reactive case reported elsewhere [27]. Conversely, for the activation process, one observes the common pattern found in reactions that have an energy threshold: the activation cross-section increases with translational energy until it eventually reaches a maximum and decreases afterwords.…”

“…The perspective view in Fig. 4 [27] among all normal modes and specified by the value of E v i ). In fact, for a given E v i , the DE fl = À1 kcal mol À1 de-activation rate constants are predicted to be typically a factor of 2 smaller than the reactive rate constants for R 27 , but about 2 times larger than the corresponding R 18 ones.…”

“…vi Calculated using the fit to the specific excitation function (columns two to four of Table 4). Calculated using the approach and data reported in [27].…”

“…In a previous paper [27], we have provided the first information on the HO 2 + O 2 atmospheric reaction with both reactants being highly vibrationally excited. However, our understanding of the collisional energy transfer behavior of highly excited HO 2 radicals (hereafter denoted as HO vibrational relaxation in such processes has been left unanswered.…”

“…Our major interest in this work is twofold: (a) provide a detailed theoretical investigation of the title vibrational relaxation process by considering HO Ã 2 radicals containing between 21 and 48 kcal mol À1 of vibrational excitation and O 2 molecules in their ground vibrational state; (b) test further our recently proposed DMBE potential energy surface for ground-doublet HO 4 [28], which has been found useful to rationalize the important OH(v) + O 3 atmospheric reaction and its reverse [28][29][30][31]27]. For OH(v) + O 3 , not only good agreement with the available experimental data has been obtained, but also the long-standing problem on the OH(v) removal reaction mechanism involving competition between vibrational relaxation and chemical reaction dynamics has been elucidated.…”