Photolysis of NO2 at multiple wavelengths in the spectral region 200–205 nm

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( 1 D2) fragment using (2+1) REMPI via the 3p 1 P1 state at 2 × 205.47 nm and the 3p 1 F3 state at 2 × 203. 5n m, and the O( 3 PJ ) fragments using (2+1) REMPI via the 4p 3 PJ states around 2 ×∼ 200 nm. Translational energy and angular distributions are extracted from the O( 1 D) and O( 3 P) product images. A growth in the population of highly excited vibrational levels of the NO X( 2 Π) 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 1 D2 state is obtained from analysis of the polarization sensitivity of the O( 1 D) 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.