Studies on spectroscopy character of C6H5N using multiconfiguration second-order perturbation theory

Complete active space self-consistent field (CASSCF) calculations with 6-31 g (d, p) basis sets were performed for a dozen of electronic states of nitrate free radical, C6H5N, and its positive and negative ions in C2v symmetry. All calculated states were valence states and their characters were discussed in detail. For all the calculated states, the accuracy of the total energies was improved by including dynamic electron correlation via the multiconfiguration second-order perturbation theory (CASPT2) method. The results suggest that the calculated transitions of 13A2 -> 13A1 and 13A2 -> 13B2 at 4303.1 and 4212.2 kJ/mol are attributed to π (b1) -> ny and π (a2) -> ny transition, respectively, while those of 13A2 -> 13B1 and 13A2 -> 11B1 at 2634.9 and 2700.4 kJ/mol belong to the mixture of nx -> π* (a2) and π (a2) -> nx transitions. The ionization energies were obtained in comparison with the photoelectron spectrum (PES) data. These above results are in agreement with the previous experimental data, which is discussed in detail.