Fully Quantum-State Resolved Study of NO2 Photodissociation: Correlated NO(2.PI..OMEGA., .nu. = 0,J,.LAMBDA.) + O(3Pj) Distributions

Abstract

Relative O(3Pj=~,~,~) spin-orbit populations correlated with specific N0[2nQ=l/2,3/2; Y = 0; J; A = II(A'), n(A")] product states were obtained following photolysis of NO2 at excess energies Zi ? = 390, 425, and 1054 cm-I. These fully quantum state-resolved measurements were carried out by recording spatial profiles of recoiling N0(213~,J,A) products using polarized radiation for photolysis and state-selective laser ionization detection. The relative O(3P,) populations correlated with each N0(213~,J,A) state show marked fluctuations at each excess energy as a function of rotational state and A-doublet component. The relative populations also fluctuate as a function of excess energy. The O(3Pj) spin-orbit population ratios, when averaged over all measurements, exhibit distributions that are colder than statistical, in agreement with previous results. In particular, we find that, on average, O(3P~):O(3P2) population ratios correlated with the ground N0(2171/2) state are colder than the corresponding ratios correlated with the excited NO(TI3/2) spin-orbit state. These results are in agreement with the state-specific calculations of Katigiri and Kat0 [J. Chem. Phys. 1993, 99, 88051 and are discussed in terms of long-range nonadiabatic transitions among electronic states correlating asymptotically with different spin-orbit states of the ground NO(TI) + O(3P) dissociation channel.

Some remarks on the photodynamics of NO2

“…This threshold behaviour has been studied using a variety of experimental approaches. [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] At higher excitation energies the decomposition occurs more rapidly with the fragmentation rate decreasing from 50 ps close to threshold to less than 80 fs 100 meV above this level. 59,60,62 At still higher excess energies in the (1) 2 B 2 state inverted vibrational profiles are observed with the peaks in the profiles occurring at progressively higher vibrational levels with increased excitation energy.…”

Dissociative multiphoton ionization of NO2 studied by time-resolved imaging

“…Excitation above the conical intersection therefore leads to rapid internal conversion and an extremely complicated absorption spectrum. 19 Above the dissociation limit to NO( 2 ⌸)ϩO( 3 P) on the X 2 A 1 surface the situation leads to equally rich dynamics, manifest, for example, in the observation of ''Ericson fluctuations'' 20 in the PHOFEX spectra 21 and in the photofragment aniostropy parameter. 22 The nuclear dynamics leading to dissociation is now generally agreed to involve a decrease in bending angle as the molecule moves from the Franck-Condon region of the à 2 B 2 state immediately accessed by the photolysis photon towards the conical intersection with the X 2 A 1 state.…”

Unimolecular Reaction of NO2: Overlapping Resonances, Fluctuations, and the Transition State

“…Recently, it has become possible to observe what we believe are experimental manifestations of overlapping resonances in a state-to-state unimolecular reaction. In this article we describe our studies of the decomposition of NO 2 − and relate them to averaged results that can be compared with statistical theories. ,,,− When resonances overlap and interact via a common continuum, they interfere, and such interference will modify the line shapes and positions, giving rise to asymmetric line shapes commonly known as “Fano profiles” …”

“…The unimolecular reaction of NO 2 has been studied extensively over the past 20 years, − ,,,− and it is not the purpose of this article to provide an exhaustive review of these thorough and detailed investigations. Rather, we concentrate on experimental manifestations of overlapping resonances and their relation to statistical descriptions of the unimolecular reaction.…”