Molecular parameters of excited molecules and ions: Part V. The methyl radical and its ions

Abstract The Franck—Condon principle was applied quantitatively to the first photoelectron bands of the CH 3 and CD 3 radicals. The intensity distributions within the fine structures of these bands can be explained satisfactorily by invoking excitations of the out-of-plane vibration ν 2 and the angle bending degenerate vibration ν 4 . The results of computation do support the planarity of the methyl radical and the methyl cation. In addition, the bond lengths of CH 3 and CH + 3 are expected to have similar magnitudes by considering the vibrational intensity appeared in the corresponding photoelectron spectra. Moreover, a Franck—Condon factor calculation on the photoelectron spectrum of the methyl anion suggested that the ion is nonplanar and has a bond angle of 100° ± 4°. Force constant calculations were carried out on CH 3 , CH + 3 and CH − 3 as well as a number of related molecules with the use of the Urey—Bradley force field. The variations in the magnitudes of the force constants obtained were discussed in the light of the bonding properties and the atomic charge distributions within these molecules.