N - K near-edge x-ray-absorption fine structures of acetonitrile in gas phase

The dynamic processes of N ( 1 s ) core-hole excitation in gas-phase C H 3 C N molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N - K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of ν ( C N ) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.