Energy partitioning in the VUV photodissociation of ClNO as a function of excitation energy

Abstract

The fluorescence of NO Rydberg states resulting from the VUV photodissociation of ClNO with synchrotron radiation between 120 and 165 nm has been studied. The excitation spectra for the production of NO A 2Σ+ v′ = 0,1,2, C 2Π v′ = 0, D 2Σ+ v′ = 0 have been measured and show by comparison with the ClNO absorption spectrum a state-to-state correlation. The internal energy content (vibrational and rotational) of the NO A 2Σ+ fragment has been determined as a function of excitation energy. The rotational level distribution of NO(A) is not of Boltzmann type but follows a Gaussian-like distribution as shown from the detailed analysis of the fluorescence spectrum obtained at 147 nm. The excess energy dependence of the rotational and vibrational energy disposal deviates strongly from statistical predictions and can be explained on the basis of a simple quasidiatomic impulsive model. The time decays of NO(A) have been recorded and the rate coefficients for quenching by ClNO was found to be larger for NO(A) resulting from ClNO photolysis than for the thermalized species. This effect is attributed to the translational excitation of the separating NO fragment.