Molecular coordinates for instantaneous normal mode calculations. II. Application to CS2 and other triatomics

Abstract

We derive and demonstrate appropriate molecular coordinates for instantaneous normal mode calculations on liquids composed of linear and bent triatomic molecules. Comparisons are made between calculations in atomic Cartesian and molecular coordinates, the latter using both laboratory-frame Euler-angle and molecular-frame rotational coordinates. Results are contrasted for coordinate systems with both rigid (with no internal degrees of freedom) and flexible molecules. The coordinate dependences of the density of states, its breakdown into translational and rotational contributions, participation ratios and instantaneous normal mode (INM) spectroscopic quantities are examined and discussed.