Predissociation dynamics of N_2 O~+ at the A ~2∑~+ state: Three pathways to form NO~+ (~1σ~+) revealed from ion velocity imaging

摘要

The predissociation dynamics of nitrous oxide ion (N_2 O ~+) at its first excited state A~2∑~+ has been investigated with ion velocity imaging by probing the NO~+ fragments. The parent ion N_2 O~+, prepared at the ground state X ~2Π (000) through (3+1) resonance-enhanced multiphoton ionization (REMPI) of jet-cooled N_2 O molecules at 360.55 nm, was excited to different vibrational levels of the A ~2∑~+ state in a wavelength range of 280-320 nm, and then predissociated to form NO~+ and N fragments. The internal energy distribution of the NO~+ fragment was determined from its ion velocity images. With the help of potential energy surfaces (PESs) of N_2 O~+, three dissociation pathways have been proposed to interpret the three kinds of NO~+ fragments with different internal state distributions: (1) the A ~2∑~+ state couples to a dissociative 1 ~4∑~- state via a bound 1 ~4Π state to form the NO~+ +N (~4S) channel, where NO~+ fragment is rotationally hot; (2) the A ~2∑~+ + state couples to dissociative states ~2∑~-/ ~2Δ via the 1 ~4Π state to form the NO~+ +N (~2D) channel, where NO ~+ fragment is also rotationally hot; (3) the A ~2∑ ~+ state couples to the high energy region of the ground state X ~2Π and then dissociates to form the NO~+ +N (~2D) channel, where NO~+ is rotationally cold.