Nonadiabatic Reactive Quenching of OH(A²Σ⁺) by H₂: Origin of High Vibrational Excitation in the H₂O Product

Abstract

The nonadiabatic dynamics of the reactive quenching channel of the OH­(A 2Σ+) + H2/D2 collisions is investigated with a semiclassical surface hopping method, using a recently developed four-state diabatic potential energy matrix (DPEM). In agreement with experimental observations, the H2O/HOD products are found to have significant vibrational excitation. Using a Gaussian binning method, the H2O vibrational state distribution is determined. The preferential energy disposal into the product vibrational modes is rationalized by an extended Sudden Vector Projection model, in which the h and g vectors associated with the conical intersection are found to have large projections with the product normal modes. However, our calculations did not find significant insertion trajectories, suggesting the need for further improvement of the DPEM.

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy with the Example of OH in the Atmosphere of WASP-33b

“…In addition, we consider a hypothetical non-LTE scenario, where the vibrational state populations have been driven away from a Boltzmann distribution, similar to that shown for the excited bending vibrational mode of H 2 O by Han et al (2022). In our non-LTE scenario, we take the molecules to have been vibrationally excited to an arbitrary peak of v = 3, with the remaining state populations following a normal distribution around this peak, as shown in Table 2.…”