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

We derive and demonstrate appropriate molecular coordinates for instantaneo us normal mode calculations on liquids composed of linear and bent triatomi c molecules. Comparisons are made between calculations in atomic Cartesian and molecular coordinates, the latter using both laboratory-frame Euler-ang le and molecular-frame rotational coordinates. Results are contrasted for c oordinate systems with both rigid (with no internal degrees of freedom) and flexible molecules. The coordinate dependences of the density of states, i ts breakdown into translational and rotational contributions, participation ratios and instantaneous normal mode (INM) spectroscopic quantities are ex amined and discussed. (C) 1999 American Institute of Physics. [S0021-9606(9 9)50821-0].