Photolysis of NO2 at multiple wavelengths in the spectral region 200-205 nm - A velocity map imaging study

Abstract

A study of the photodissociation dynamics of NO2 in the 200-205 nm region using resonance enhanced multiphoton ionization (REMPI) in conjunction with the velocity map imaging technique is presented. We chose this region because it allowed the use of a single laser to photodissociate the NO2 molecule and probe both the O(D-1(2)) fragment using (2+1) REMPI via the 3p'P-1(1) state at 2 x205.47 nm and the 3p'F-1(3) state at 2 x203.5 nm, and the O(P-3(J)) fragments using (2+1) REMPI via the 4p P-3(J) states around 2 x similar to 200 nm. Translational energy and angular distributions are extracted from the O(D-1) and O(P-3) product images. A growth in the population of highly excited vibrational levels of the NO X((II)-I-2) co-fragment is found as the dissociation wavelength decreases. These are compared with similar trends observed previously for other triatomic O-atom containing molecules. Detailed information on the electronic angular momentum alignment of the D-1(2) state is obtained from analysis of the polarization sensitivity of the O(D-1) images using the two resonant intermediate states. The angular dependence of the potential energy in the exit channels is examined using long-range quadrupole-dipole and quadrupole-quadrupole interaction terms, from which molecular-frame multipole moments of the total angular momentum of the recoiling O atoms have been calculated. Comparison with the experimentally derived multipole moments is used to help provide insight into the dissociation mechanism.