A microwave and quantum chemical study of cyclopropaneselenol.

The microwave spectrum of cyclopropaneselenol, C 3H 5SeH, has been investigated in the 21.9-80 GHz frequency range. The microwave spectra of the ground vibrational state of five isotopologues of cyclopropaneselenol (C 3H 5 (82)SeH, C 3H 5 (80)SeH, C 3H 5 (78)SeH, C 3H 5 (77)SeH, and C 3H 5 (76)SeH) of one conformer, as well as the spectra of two vibrationally excited states of each of the C 3H 5 (80)SeH and C 3H 5 (78)SeH isotopologues of this rotamer, have been assigned. The H-C-Se-H chain of atoms is synclinal in this conformer, and there is no indication of further rotameric forms in the microwave spectrum. The b-type transitions of the ground vibrational state of the more abundant species C 3H 5 (80)SeH and C 3H 5 (78)SeH were split into two components, which is assumed to arise from tunneling of the proton of the selenol group between two equivalent synclinal potential wells. The tunneling frequencies were 0.693(55) MHz for C 3H 5 (80)SeH and 0.608(71) MHz for C 3H 5 (78)SeH. The microwave study has been augmented by high-level density functional and ab initio quantum chemical calculations, which indicate that the H-C-Se-H dihedral angle is approximately 75 degrees from synperiplanar (0 degrees).