Simulation of effective vibrational-translational energy exchange in collisions of vibrationally excited OH with O2 on the model potential energy surface. Can the relaxation of OH(v) be one-quantum for low and multiquantum for high v?

Abstract

The collision of OH with the oxygen molecule is studied by the trajectory simulation technique on the model potential energy surface of OH + 0 2 -0 3 + H chemical reaction. Although the reaction channel is closed, we aim to demonstrate that the L-shape of the OH + 0 2 valley leads to the effective coupling of OH(v) vibration with the relative motion of collisional partners and therefore explains the high value of the vibrational relaxation rate constant observed experimentally. The characteristic feature of the mechanism considered is the predominance of one-quantum relaxation for low and multiquantum transitions for high OH vibrational levels. To estimate state-to-state vibrational relaxation rate constants, the method of dynamical corrections of transition state theory is used. The expression for the rate constant consists of a transition state term and a correction factor, determined in two-dimensional classical trajectory calculations. We also demonstrate the instability of motion on the potential energy surface with the L-shape valley, resulting from the scattering of the trajectory on the "comer" of the potential energy surface and the presence of regular and chaotic motions.

Dynamics Study of the OH + O2 Branching Atmospheric Reaction. 3. Dissociation in Collisions of Vibrationally Excited Reactants

“…For example, the reaction leads to OH in vibrationally excited states with quantum numbers up to V′ ) 9. [2][3][4][5][6][7][8][9][10][11][12][13] In turn, photodissociation of ozone within the Hartley band yields vibrationally excited molecular oxygen with a distribution peaking in the vicinity of V′′ ) 14 and V′′ ) 27 14 according to the reaction Recently, another bimodal distribution has been observed in the photodissociation of ozone at 266 nm with peaks near V′′ ) 9 and V′′ ) 5. 15 An additional source of vibrationally excited oxygen molecules in the stratosphere is the reaction 16 with O 2 populating vibrationally excited levels up to V′′ ) 13.…”

Experimental Detection of Hydrogen Trioxide

“…reaction, the source of vibrationally excited hydroxyl radicals ahose einission spectrum is related to night-sky afterglow (3)(4)(5)(6)(7)(8)(9). Despite its relevance to atmospheric chemistry and its intrinsic fundarnental interest, H 0 3 has not been experimentally detected to date, and it has remained open whether it can survive dissociatioil into 0, and OH.…”

“…Characterization of HO, as an intermediate. rather than as a fleeting HOi'O, con~plex or a transition state, has a direct bearing on atmospheric chemistry, in particular concerning its role in night-sky afterglo\\, and regarding the accurate kinetic modeling of the H + 0, reaction and the collisional quenching of vibrationally excited hydroxyl radicals by O,, two processes of current interest (7,24), owing to their i~nportance in at~nospheric chemistry. …”

OH(v)+O3: Does chemical reaction dominate over non-reactive quenching?

“…We have reported a QCT study of the reaction OHv 0 3 9 O 3 using a recently published DMBE potential energy surface for ground state HO 4 . The calculations have shown that the title reaction may occur both via capture-type and barrier-type mechanisms, depending on the reactant initial conditions, especially the degree of OH vibrational excitation.…”

“…The Letter is organized as follows. Section 2 gives a brief survey of the HO 4 2 A DMBE potential energy surface, while the computational method is described in Section 3. The dynamics results are presented and discussed in Section 4, and the major conclusions in Section 5.…”