Abstract

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 2A′←X̃ 2A″ band and a higher-energy band system assigned to the C̃ 2A″←X̃ 2A″ 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 ΔfH0(HNCN) were determined to be 2.80±0.03 eV and 3.35±0.03 eV, respectively.

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