Ab Initio Study of the Spectroscopy of CH3N and CH3CH2N.

Complete active space (CAS) calculations with 6-311g(3df,3pd) basis sets were performed for a large number of electronic states of the nitrate free radical (CH3N/CH3CH2N) and their positive and negative ions. All calculated states are valence states, and their characters are discussed in detail. To investigate the Jahn−Teller effect on the CH3N radical, Cssymmetry was used for both CH3N and CH3CH2N in calculations. The results (CASPT2 adiabatic excitation energies and CASSI oscillator strengths) suggest that the calculated transitions of CH3N at 32172 and 32139 cm-1are attributed to the 23A‘ ‘ → 13A‘ ‘ and 13A‘ → 13A‘ ‘, respectively, which is in accordance with the Ã3E → 3A2emission spectrum at T0 31 817 cm-1. The calculated transitions of CH3CH2N at 334 nm are attributed to the 13A‘ ‘ → 23A‘ ‘ and 13A‘ ‘ → 13A‘, respectively, which is in accordance with the UV absorption spectrum of a series of 11 bands beginning at 335 nm. The vertical and adiabatic ionization energies were obtained to compare with the PES data. These results are in agreement with previous experimental data, which is discussed in detail. [ABSTRACT FROM AUTHOR]