A Parameter to Quantify Molecular Quasilinearity

A simple parameter is proposed for expressing the quasilinearity of molecules in a quantitative way. The parameter γ0 is defined on the basis of a discussion of the separation of variables in the Born-Oppenheimer approximation. The parameter γ0 assumes the value +1 for bent molecules and -1 for linear molecules. The range from -1 to +1 traces the transition of a vibrational degree of freedom in the linear configuration of a polyatomic molecule into a rotational degree of freedom in the bent configuration. The sequence of molecules along this parameter is shown and model calculations are carried out to further illustrate the physical interpretation of the parameter.