Loss of HCN from the pyrimidine molecular ion: A computational study

The potential energy surface (PES) for the loss of HCN from the pyrimidine molecular ion has been explored using quantum chemical calculations. Possible reaction pathways to form five C₃H₃N⁺· isomers have been obtained with Gaussian 4 model calculations. The rate constant for the HCN loss and the product branching ratio have been calculated using the Rice-Ramsperger-Kassel-Marcus theory on the basis of the obtained PES. The resultant rate constant agrees with the previous experimental result. By a kinetic analysis, it is proposed that the formation of CH=CHC≡NH ⁺· is favored near the dissociation threshold, while the formation of CH=CHN≡CH⁺· is favored at high energies.