Rotational energy analysis for rotating–vibrating linear molecules in classical trajectory simulation

Abstract

A method has been developed to evaluate the rotational energy of a rotating–vibrating linear molecule in classical trajectory simulation. The method is based on our finding that the component of the angular momentum perpendicular to the figure axis which closely approximates the pure rotational angular momentum is a fairly good constant of motion. Classical kinetic energy of the system has been reorganized to separate the rotational and vibrational parts according to the above concept. Time evolution of the rotational energy thus evaluated shows much less irregular behavior than the ones evaluated with the previous methods over a wide range of rotational and vibrational energies. Combined with the method for mode-specific vibrational energy analysis reported previously, the present method allows a reliable separation of the total energy into each degree of freedom. In particular, the accuracy of the present method seems to be good enough for the rotational energy determination at an instantaneous configuration point along a trajectory, enabling the classical study of real time dynamics.