Photodissociation dynamics of HN 3(DN 3) + hv → H(D)+ N 3

Abstract

The photolysis of HN 3/DN 3 to give H/D and N 3 is investigated at different photolysis wavelengths: 266, 248, 222, 193 and 122 nm. Nascent H/D atoms are characterized via Doppler and polarization spectroscopy using laser-induced fluorescence in the VUV. The following quantum yields have been found: H−N 3 (266 nm) = 0.04, H−N 3 (248 nm) ≈ D−N 3 (248 nm) = 0.20, and H−N 3 (193 nm) ≈ D−N 3 (193 nm) = 0.14. At a photolysis wavelength of 266 nm most of the available energy goes into product translation, 〈 E kin〉 = 5820 cm −1, while the internal energy of the N 3 fragment is fairly low, 〈 E int(N 3)〉 = 1250 cm −1. At 248 nm the values are 6640 and 3150 cm −1, respectively. Thus additional excess energy is preferentially released as internal energy of the N 3 radical. This trend is less pronounced when the excitation wavelength is set to 222 or 193 nm. At 122 nm the kinetic energy of the photofragments is smaller than in the 193 nm experiment. At 266 and 248 nm the spatial distribution of the photofragments is described by a strongly negative anisotropy parameter indicating a definite preference for a perpendicular alignment of the electronic transition moment and the recoil velocity vector. At 222 and 193 nm the anisotropy parameter is close to zero, while the VUV photolysis results in a slightly positive anisotropy parameter. These experimental findings indicate that the access to different electronic states of HN 3/DN 3 is gained as the photolysis wavelength is varied from 266 to 122 nm.