Photodissociation of NO2. Internal energy distribution and anisotropies in the fragments

The near-UV photodissociation of NO₂ has been investigated at excess energies from −600 up to 1700 cm⁻¹ above the NO X ν = 1 + O³P dissociation limit. A complete analysis of the NO X ν = 1 fragment, including internal and translational energy as well as the angular properties of its vectorial parameters, has been carried out using REMPI combined with TOF mass spectrometry. The high-precision state-selective measurements of the NO fragment velocity have been used to evaluate the internal energy of the O atoms formed in coincidence. Concerning the internal energy of the NO X ν = 1 fragment, two types of final state distributions of the fragments have been found; the difference depending upon the excess energy with respect to the NO X ν = 1 + O₃P dissociation limit. Above the threshold, statistical rotational behaviour with nonvanishing anisotropies has been observed. Below the threshold, an efficient R→V transfer, allowed by a significant molecular distortion, was detected. The influence of the parent rotation on the NO fragment rotational distribution is discussed.