Showing papers by "Maciej J. Nowak published in 1995"

Anharmonic contributions to the inversion vibration in 2-aminopyrimidine

Abstract: The out‐of‐plane vibrations of the amino group in 2‐aminopyrimidine have large amplitudes, and cannot be properly described within the harmonic approximation. The normal mode analysis carried out at this level of approximation at the restricted Hartree–Fock level and at the second‐order Mo/ller–Plesset perturbation theory level failed to match the experimental transition frequency of ν≊200 cm−1 of the inversion vibration in this compound. In an effort to better understand this vibration motion, we went beyond the harmonic approximation. The inversion vibration was treated as being uncoupled from all other nuclear degrees of freedom. An internal coordinate (ω) was chosen whose displacement mimicked the out‐of‐plane distortion of the amino group during the inversion vibration. Electronic energy was calculated at the second‐order Mo/ller–Plesset perturbation theory level at selected values of ω to form a double‐well curve describing a model potential within which the nuclei move during the vibration. This po...