Quasi-symmetric top molecule approach to the rotational-vibrational problem of CH 3XY molecules: Application to CH 3C 15N
A new approach to the rotational-vibrational problem of molecules of the CH 3XY type is proposed. The approach can be applied equally well to either a symmetric top or an asymmetric top CH 3XY molecule. The molecule is considered as vibrating, internally rotating about the CX bond of the effectively bent CXY skeleton, and rotating in space. The zeroth-order approximation, in which the CXY bending motion and internal and overall rotations are explicitly taken into account, is discussed. The approach is applied to the analysis of the rotational spectrum of [ 15N]methyl cyanide in the ground and first and second excited states of the CCN bending mode.