Observation of rotationally dependent fine-structure branching ratios near the predissociation threshold N(2D5/2,3/2) + N(2D5/2,3/2) of14N2

Abstract

Photofragment spin–orbit fine-structure branching ratios have long been predicted to depend on the rotational quantum number J′ by theory near the dissociation thresholds of several diatomic molecules, while this has rarely been observed in any photodissociation experiments yet. Here, we measured the fine-structure branching ratios N(2D5/2)/N(2D3/2) produced in the N(2D5/2,3/2) + N(2D5/2,3/2) channel at the b′1Σu+( v = 20) state of14N2by using our vacuum ultraviolet (VUV)-pump–VUV-probe time-sliced velocity-mapped ion imaging setup. It is found that14N2almost exclusively dissociates into the spin–orbit channel N(2D5/2) + N(2D3/2) at low rotational levels and gradually approaches the statistical or diabatic limit by distributing all possible spin–orbit channels at higher rotational levels. The strongly rotationally dependent fine-structure branching ratios should be due to the increasing strength of nonadiabatic Coriolis interaction among various dissociative states in the so-called “recoupling zone” as J′ increases. They are supposed to provide unprecedented information on the near threshold photodissociation dynamics of14N2.