Nonadiabatic dynamics in a forest of coupled states: Electronic state branching in the VUV photodissociation of N2

Abstract

Multi-state electronic dynamics at higher excitation energies is needed for the understanding of a variety of energy rich situations, including chemistry under extreme conditions, vacuum ultraviolet (VUV) induced astrochemistry, and attochemistry. It calls for an understanding of three stages, energy acquisition, dynamical propagation, and disposal. It is typically not possible to identify a basis of uncoupled quantum states that is sufficient for the three stages. The handicap is the large number of coupled quantum states that is needed to describe the system. Progress in quantum chemistry provides the necessary background to the energetics and the coupling. Progress in quantum dynamics takes this as input for the propagation in time. Right now, it seems that we have come of age with potential detailed applications. We here report a demonstration to a coupled electron-nuclear quantum dynamics through a maze of 47 electronic states and with attention to the order in perturbation theory that is indicated using propensity rules for couplings. Close agreement with experimental results for the VUV photodissociation of 14N2 and its isotopomer 14N15N is achieved. We pay special attention to the coupling between two dissociative continua and an optically accessible bound domain. The computations reproduce and interpret the non-monotonic branching between the two exit channels producing N(2D) and N(2P) atoms as a function of excitation energy and its variation with the mass.

Nonadiabatic quantum dynamics explores non-monotonic photodissociation branching of N2 into the N(4S) + N(2D) and N(4S) + N(2P) product channels

“…35 and adiabatized as explained in ref. 65. The derived adiabatic data along with presently computed spin-orbit coupling elements are given in Fig.…”

“…60 Nowadays the quantum dynamical approaches [61][62][63][64] have reached a level where they can offer a computational tool which allowed us to follow the time-evolution of an electronic wave packet travelling in the forest of electronic states, beyond the states directly accessed from the ground electronic state. 65 The approach has been applied to explore the mechanism of dissociative ionization of N 2 [66][67][68] and ultrafast electronic excitation and dissociation. [69][70][71][72] We recently computed a realistic energy dependence in the dissociation branching arising from excitation of different single vibrational levels of 1 S + u electronic states of N 2 .…”

“…[69][70][71][72] We recently computed a realistic energy dependence in the dissociation branching arising from excitation of different single vibrational levels of 1 S + u electronic states of N 2 . 65,73 These computations started from the molecule in the ground electronic state and excited it by a polarized laser pulse of a very long duration and of the required mean energy. In the present work we make a step further and present the results of the branching into the channels N( 4 S) + N( 2 D) (Channel 1) and N( 4 S) + N( 2 P) (Channel 2) accessed through the excited 1 P u states of N 2 .…”

“…60 Nowadays the quantum dynamical approaches 61–64 have reached a level where they can offer a computational tool which allowed us to follow the time-evolution of an electronic wave packet travelling in the forest of electronic states, beyond the states directly accessed from the ground electronic state. 65…”

Observation of Continuum State Dissociation Enables the Determination of N2 Bond Dissociation Energy to Spectroscopic Accuracy

“…It has long been known that N 2 undergoes indirect predissociation with long enough lifetime to have rotationally resolved dissociation cross sections, where the directly excited bound levels couple with continuum states to dissociate. − While the predissociation dynamics of the bound states have been well studied, direct observation of the continuum-state dissociation has remained elusive. Here we report the observation of the continuum-state dissociation of 14 N 2 and 15 N 2 into the channel N­( 2 D 5/2,3/2 )+N­( 2 D 5/2,3/2 ) for the first time, which is demonstrated in Figure .…”