Photodissociation and photoisomerization pathways of the HNCN free radical

The photodissociation spectroscopy and dynamics of the HNCN free radical have been investigated by fast beam photofragment translational spectroscopy. Predissociative transitions for both the B̃ 2A8←X̃ A9 band and a higher-energy band system assigned to the C̃ 2A9←X̃ A9 band were observed. Photofragment mass distributions indicate that N2 loss is the primary dissociation pathway. Translational energy distributions reveal a resolved vibrational structure of the N2 fragment, suggesting that the HNCN radical first isomerizes to a cyclic HCN2 intermediate. A dissociation mechanism is proposed in which electronically excited HNCN undergoes internal conversion to the ground state, followed by isomerization to cyclic HCN2 and dissociation through a tight three-center transition state. The HNCN bond dissociation energy D0 and heat of formation D fH0~HNCN! were determined to be 2.8060.03 eV and 3.3560.03 eV, respectively. © 2001 American Institute of Physics. @DOI: 10.1063/1.1367411#