Fully state-selected VMI study of the near-threshold photodissociation of NO2: variation of the angular anisotropy parameter

Velocity-map ion imaging (VMI) has been used to study the angular distribution of the NO fragment generated in the photodissociation of NO2 at a variety of photolysis wavelengths. Images were recorded for the channels NO (II1/2)-I-2 (v ''(NO) = 0, J ''(NO)= 3/2, 11/2 and 21/2) + O (P-3(2,1)), for excitation energies ranging from the onset (E-av1/hc = 0 cm(-1)) to E-avl/hc similar or equal to 900 cm(-1). The angular anisotropy parameter beta was obtained as a function of available energy. Photofragment multiphoton ionization (PHOMPI) spectra were also recorded in the energy range E-avl/hc = 0 cm(-1) for each of these channels. Large. uctuations of b as a function of E-avl were found in all observed dissociation channels. These variations are discussed in terms of the lifetimes of the originally photoexcited overlapping resonances in the A B-2(2) state of NO2, the dynamics of which are strongly influenced by nonadiabatic coupling with the X (2)A(1) state. The potential use of this photolysis process for production of cold oxygen atoms is discussed.