Electronic Quenching of OH A ²Σ⁺ Induced by Collisions with Kr Atoms

Abstract

Electronic quenching of OH A (2)Σ(+) by Kr was investigated through experimental studies of the collision cross sections and the OH X (2)Π product state distribution. The quenching cross sections decrease with increasing rotational excitation in the excited OH A (2)Σ(+) electronic state. The OH X (2)Π products of quenching exhibit a significant degree of rotational excitation but minimal vibrational excitation. Complementary theoretical studies of the OH (A (2)Σ(+), X (2)Π) + Kr potential energy surfaces (PESs), nonadiabatic coupling, and quasiclassical trajectory calculations were carried out to elucidate the quenching dynamics. Accurate PESs for the two lowest diabatic states of A' symmetry were computed along with the angularly dependent coupling between them. Coupling in nearly linear HO-Kr configurations provides the mechanism for the observed electronic quenching. A deep attractive well on the OH A (2)Σ(+) + Kr PES facilitates access to this region of strong coupling. Surface-hopping quasiclassical trajectory calculations yielded quenching cross sections and a OH X (2)Π product rotational distribution in good accord with experimental observations.

Parity-Dependent Rotational Energy Transfer in CN(A2Π, ν = 4, j F1ε) + N2, O2, and CO2 Collisions

“…This may be evidence for a more strongly preferred orientation leading to total quenching for O 2 and CO 2 , which is then washed out more effectively than that for the other colliders as the rotational speed of the CN increases. 52,53 …”

Collisional depolarisation in electronically excited radicals

“…is symmetric under such a reflection, so is labelled 2A . These three adiabatic potential energy surfaces have been calculated by K los et al at the MRCISD+Q level of theory [30].…”

“…As states of different symmetry cannot couple electronically, the 1A state is the same in the adiabatic and diabatic representations. The diabatic states Π A and Σ A are related to the adiabatic states by an orthogonal transformation [26,30]:…”

“…A secondary focus of this review is on the interplay between electronically adiabatic (RET, rotationally elastic and inelastic depolarisation) and non-adiabatic (quenching) processes in systems such as OH(A) + Kr that display significant electronic quenching. This has been explored in several recent papers [26,27,30], and informs similar studies with larger molecules, for example H 2 [31,32]. Analysis of collisions where the products remain on the excited PES can provide information about which kinds of collisions do, and do not, lead to quenching or reactive outcomes.…”

“…The elastic depolarisation cross sections can be obtained by fitting the spin-rotation state resolved data in the same way as the total data, i.e. using equation (32) for orientation and equation (30) for alignment.…”