NO angular distributions in the photodissociation of (NO)2 at 213 nm: Deviations from axial recoil

Abstract

Angular distributions of selected rotational states of NO(A 2 ⌺ ϩ ,ϭ0) products obtained in the 213 nm photodissociation of (NO) 2 have been determined in a molecular beam by using the photofragment ion imaging technique. Specifically, images of NO(A,ϭ0) products in Nϭ0, 11, and 19 have been recorded, for which the maximum energies available to the NO(X 2 ⌸) products are 2038, 1774, and 1278 cm Ϫ1 , respectively. The recoil anisotropy parameter of the photofragments, ␤ eff , decreases significantly at low center-of-mass translational energies from its maximum value of 1.36Ϯ0.05, and depends strongly on the rotational angular momentum of the photoproducts. This behavior is described well by a classical model that takes into account the transverse recoil component mandated by angular momentum conservation. For each of the observed NO(A) N states, highly rotating NO(X) levels are produced via planar dissociation, and the angular momenta are established at an interfragment separation of about 2.6 Å. For most of the center-of-mass translational energy range, both corotating and counterrotating fragments are produced, but at the lowest energies, only the latter are allowed. The correlated rotational energy distributions exhibit deviations from the behavior predicted by phase space theory, suggesting that exit-channel dynamics beyond the transition state influences the product state distributions. In this study, a new method for image reconstruction is employed, which gives accurate angular distributions throughout the image plane.

Femtosecond Time‐Resolved Photoelectron Spectroscopy

“…These time scales were found to match for excitation wavelengths below 220 nm and indicated a lifetime contraction with decreasing pump wavelength. While an effective photodissociation lifetime additionally depends on the dimer Rydberg lifetime, these results corroborate photofragment imaging studies reported by Demyanenko et al 178 that find higher fragment anisotropy for higher excitation energies in this region, suggested to result from shortened dimer lifetimes.…”

Time‐Resolved Photoelectron Spectroscopy of Nonadiabatic Dynamics in Polyatomic Molecules

“…The observed NO(A, 3s) product state distributions supported the notion of a planar dissociation involving restricted intramolecular vibrational energy redistribution (IVR) [176]. A scheme for studying NO dimer photodissociation dynamics via TRPES is depicted in Fig.…”

Exit channel dynamics in the ultraviolet photodissociation of the NO dimer: (NO)2→NO(A 2Σ+)+NO(X 2Π)

“…Following photolysis, the dimer undergoes fast dissociation, and NO(A 2 ⌺ ϩ ,N) products are detected by resonance enhanced multiphoton ionization ͑REMPI͒ and velocity map ion imaging, providing velocity and angular distributions of state-selected products. The experiments are similar to those carried out at 213 nm, 12 and therefore, only procedures that have changed are discussed in detail.…”

“…In a recent study ͑Paper I͒, 12 we examined in detail the angular distributions obtained in the photodissociation of (NO) 2 at 213 nm (E † ϭ2038 cm Ϫ1 ) for specific NO(A) rotational states. Using the velocity map ion imaging technique, we obtained speed-dependent recoil anisotropy parameters ␤ eff from images of selected NO(A,N) states.…”