Stereodynamic Control of Collision-Induced Nonadiabatic
Dynamics of NO (A2Σ+)
with H2, N2, and CO: Intermolecular Interactions
Drive Collision Outcomes
posted on 2021-10-04, 16:36authored byJosé
L. Guardado, David J. Hood, Kate Luong, Nathanael M. Kidwell, Andrew S. Petit
Intermolecular
interactions, stereodynamics, and coupled potential
energy surfaces (PESs) all play a significant role in determining
the outcomes of molecular collisions. A detailed knowledge of such
processes is often essential for a proper interpretation of spectroscopic
observations. For example, nitric oxide (NO), an important radical
in combustion and atmospheric chemistry, is commonly quantified using
laser-induced fluorescence on the A2Σ+ ← X2Π transition
band. However, the electronic quenching of NO (A2Σ+) with other molecular species provides
alternative nonradiative pathways that compete with fluorescence.
While the cross sections and rate constants of NO (A2Σ+) electronic quenching have been experimentally
measured for a number of important molecular collision partners, the
underlying photochemical mechanisms responsible for the electronic
quenching are not well understood. In this paper, we describe the
development of high-quality PESs that provide new physical insights
into the intermolecular interactions and conical intersections that
facilitate the branching between the electronic quenching and scattering
of NO (A2Σ+) with H2, N2, and CO. The PESs are calculated at the EOM-EA-CCSD/d-aug-cc-pVTZ//EOM-EA-CCSD/aug-cc-pVDZ
level of theory, an approach that ensures a balanced treatment of
the valence and Rydberg electronic states and an accurate description
of the open-shell character of NO. Our PESs show that H2 is incapable of electronically quenching NO (A2Σ+) at low collision energies; instead, the
two molecules will likely undergo scattering. The PESs of NO (A2Σ+) with N2 and
CO are highly anisotropic and demonstrate evidence of electron transfer
from NO (A2Σ+) into the
lowest unoccupied molecular orbital of the collision partner, that
is, the harpoon mechanism. In the case of ON + CO, the PES becomes
strongly attractive at longer intermolecular distances and funnels
population to a conical intersection between NO (A2Σ+) + CO and NO (X2Π) + CO. In contrast, for ON + N2, the conical
intersection is preceded by an ∼0.40 eV barrier. Overall, our
work shines new light into the impact of coupled PESs on the nonadiabatic
dynamics of open-shell systems.