Effects of spin–orbit coupling on the quantum dynamics and vibronic structure of the B̃2E′ state of NO3

The nitrate radical (NO3) is a fascinating species and has been studied for decades. Nevertheless, some aspects still remain elusive. The effects of Jahn–Teller and pseudo-Jahn–Teller interactions on the quantum dynamics of NO3 have been studied extensively, but the influence of spin–orbit (SO) coupling has received little attention. The present work aims to fill this gap. A recently developed diabatic potential energy model [F. Fritsch and W. Eisfeld, J. Chem. Phys. 164, 074107 (2026)] is used to study the influence of SO coupling on the quantum dynamics. First, the impact on the nonadiabatic population dynamics following excitation to the B̃2E′ state of NO3 is explored. This excitation, relevant for the photodetachment of NO3− and photodissociation of NO3, is complemented by a comparison with the impact of NO3− vibrational pre-excitation. The latter turned out to have a much more pronounced effect than SO coupling. Second, the vibronic eigenstates of the B̃2E′ state are examined, which reveal the more subtle effects of SO coupling. The experimentally observed splitting of the 0–0 B̃2E′ ← X̃2A2′ transition is reproduced accurately, and additional insight into the spin-vibronic structure of the B̃2E′ state is provided and discussed in detail.