Mode-specific energy analysis for rotating-vibrating triatomic molecules in classical trajectory simulation

Abstract

A method for the mode-specific energy analysis in a classical trajectory calculation is developed. The pure rotational energy is evaluated by invoking the Eckart condition. To evaluate the vibrational energy in each normal mode, the vibrational velocity is divided into two parts, the angular motion part and the angular motion free part, and the latter is analyzed with the Cartesian and internal coordinate systems. The potential energy of each normal mode is also evaluated in the two coordinate systems. A simple algorithm to include some anharmonicity correction is presented. Sample calculations with nonreacting triatomic molecules, H2O and HCN, show that the internal coordinate system is more adequate than the Cartesian, especially for the linear molecule HCN. An excellent result is obtained for the product (CHO+) of a reaction, suggesting that the present method is adequate for the mode-specific energy analysis of classical trajectory results.