Directional Characteristics of the Moments of the Dipole-Oscillator-StrengthDistribution of Molecules: H2 and H2O

摘要

We report polarization propagator calculations within the random-phaseapproximation of several isotropic moments and their directional components of the dipole-oscillator-strength distribution of H, and of H2O. The calculations show that there is strong dependence on the polarization direction of the incoming beam. The dependence of the moments on the molecular geometry is also discussed. In particular, the mean excitation energy for stopping is found to be very directionally sensitive, leading to the necessity of using directionally specific mean excitation energies when discussing oriented targets. It is possible that the sample phase dependence of the stopping power of water may be in part due to directional effects in I(zero). A transferable bond mean excitation energy for the O-H bond is calculated, and is found to be constant within +/-1% for not less than H--O--H from 95 deg to 120 deg at constant bond length R(sub OH). It agrees well with previous results.