Computer simulation studies of IR laser excitation of water on a metal surface
The study focuses on the excitation of water modes. The laser field is simulated as an oscillatory time-dependent external electrical field that interacts with the molecular dipoles. Unrealistically high field strengths of the order of 10^10 V/m were used in order to observe significant energy absorption and also molecular desorption on the time scale from 10 to 20 ps. Frequencies of 400, 1700, and 3750 cm^-1 were chosen to excite the molecule in the librational, bending, and stretching modes, respectively. The rates for desorption of isolated molecules are substantially lower for excitation in the bending and stretching modes than for excitation in the librational modes. At higher adsorbate coverages, intermolecular energy transfer plays a major role in the behavior of molecules in the adsorbate layer.