X‐ray scattering by water molecules studied by using synchrotron radiation

The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle‐dispersive‐type diffractometer and synchrotron radiation as an X‐ray source. A silicon (111) monochrometer was used to obtain incident X‐rays with the wavelengths of (1.543/ n ) Å ( n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [ s = (4π/λ) sin Å] larger than 8 Å −1 . The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å −1 . Experimental difference intensities Δσ ee and Δσ ne were obtained separately by combining the X‐ray and high‐energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double‐zeta plus polarization functions.