Molecular dynamics simulations and hyperspherical mode analysis of NO in Kr crystals with the use of ab initio potential energy surfaces for the Kr-NO complex

The dynamics of structural relaxation of NO doped Kr solids on electronic excitation of the NO molecule has been characterized by molecular dynamics simulations and by normal and hyperspherical mode analysis, with special emphasis on the effects of the anisotropy of the Kr-NO interaction which has been modeled by ab initio potential energy surfaces (PESs). The time evolution of the cage radius and the radial distribution function for the ground and excited states have been calculated for various orientations of the molecular axis with respect the Kr atom matrix with the NO molecule treated as a rigid rotor. The ab initio PESs, considered in previous work, seem to be too repulsive when compared with potentials fitted to spectroscopic data, and this is more evident for the first Ryberg state than for the ground state, where effects of potential anisotropy are less important. The first shell response shows a relative increase, up to similar to 10%, of the excited state equilibrium radius with respect to that of the ground state, while experiments indicate that such an increase should be less than 5%. The kinetic energy power spectrum method, presented in a previous work, has been applied to the total kinetic energy T(t) and to two characteristic quantities of the hyperspherical mode analysis, the hyperradial energy T-rho(t) and the grand angular energy T-Lambda(t) for NO molecular axis orientations of 67 degrees and 90 degrees, respectively, which represent the cases of the largest and smallest lattice distortions in the radial distribution function (RDF) of the atoms in the matrix for the excited state. The band structures of the calculated frequency spectra reveal a blue shift with respect to the case of the isotropic potentials used previously, and this is connected to the different lattice equilibrium structures for 67 degrees and 90 degrees directions. (c) 2008 Wiley Periodicals, Inc.