VIBRATIONAL EFFECTS ON CROSS-SECTIONS FOR ELASTIC-SCATTERING OF X-RAYS AND FAST ELECTRONS BY H2O MOLECULES

Waller-Hartree and first Born cross sections for the elastic scattering of X-rays and fast electrons by H2O are calculated for 80 geometries of the H2O molecule using self-consistent-field electronic wave functions of good quality. The cross sections are then averaged over the five lowest vibrational states with wave functions calculated using the discrete variable representation. The differences between the vibrationally averaged cross sections and their equilibrium counterparts are less than 1.3% and 3% for X-ray and electron scattering respectively. The effects are greater in states with a stretch excited than a bend.