Spin–orbit predissociation dynamics of NeOH (X 2Π)

Abstract

A joint theoretical–experimental study has been carried out to examine the unimolecular dissociation dynamics of NeOH (X ²Π) complexes containing spin–orbit excited OH radicals. The spin–orbit predissociation process is a direct manifestation of the difference in the two potential-energy surfaces (PESs) required to describe the interaction of Ne (¹S₀) with the OH radical in its ground (X ²Π) electronic state. The theoretical investigation involved the determination of the ab initio PESs as well as the energies and widths of the NeOH resonances correlating with the spin–orbit excited state of OH (X ²Π_1/2). In addition, the redistribution of predissociation flux is mapped out as a function of the fragment separation using the quantum flux method. Experimentally, the NeOH resonances derived from the spin–orbit excited state of OH have been observed by stimulated emission pumping (SEP). The energies and linewidths of the predissociative resonances are extracted from the SEP spectra and compared with theoretical predictions. A dramatic increase in the spin–orbit predissociation lifetime is observed upon intermolecular stretching excitation which principally reflects the reduced splitting between the two PESs with increasing intermolecular separation. Comparison of the experimentally measured and theoretically calculated observables provides a stringent test of the ab initio PESs and insight into the photodissociation mechanism.