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

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(1D2) fragment using (2+1) REMPI via the 3p'1P1 state at 2 ×205.47 nm and the 3p'1F3 state at 2 ×203.5 nm, and the O(3PJ) fragments using (2+1) REMPI via the PJ states around 2 ×∼200 nm. Translational energy and angular distributions are extracted from the O(1D) and O(3P) product images. A growth in the population of highly excited vibrational levels of the NO X(2Π) 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 1D2 state is obtained from analysis of the polarization sensitivity of the O(1D) 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.