Photodissociation dynamics of pyrimidine.

Photodissociation of pyrimidine at 193 and 248 nm was investigated separately using vacuum ultraviolet photoionization at 118.4 and 88.6 nm and multimass ion imaging techniques. Six dissociation channels were observed at 193 nm, including C₄N₂H₄→C₄N₂H₃+H and five ring opening dissociation channels, C₄N₂H₄→C₃NH₃+HCN, C₄N₂H₄→2C₂NH₂, C₄N₂H₄→CH₃N+C₃NH, C₄N₂H₄→C₄NH₂+NH₂, and C₄N₂H₄→CH₂N+C₃NH₂. Only the first four channels were observed at 248 nm. Photofragment translational energy distributions and dissociation rates indicate that dissociation occurs in the ground electronic state after internal conversion at both wavelengths. The dissociation rates were found to be >5×10⁷ and 1×10⁶ s^-1 at 193 and 248 nm, respectively. Comparison with the potential energies from ab initio calculations have been made. [ABSTRACT FROM AUTHOR]