Electron-Diffraction Study of Water and Heavy Water

Publisher Website
Google Scholar
Abstract
The structures of gaseous H2O and D2O were investigated using the sector‐microphotometer method of electron diffraction. Structural parameters and estimated standard errors for H2O included the mean bond length rg(OH) = 0.976±0.003 Å, rms amplitude lg(OH) = 0.0666±0.003 Å, and mean HOH angle αg = 107.2°±3°. Corresponding values for D2O were 0.970±0.0025 Å, 0.564±0.002 Å, and 104.2°±3°. Results agreed with spectroscopic values to within the larger limits of error of the diffraction results. Analyses were based on the radial distribution method and on a new automatic ``smooth‐background'' method. Observed atomic intensities deviated significantly at small scattering angles from intensities calculated using the conventional approximations. The resulting discrepancy led to a greater uncertainty in structural parameters than did the random experimental intensity errors. This almost universally neglected source of error is briefly discussed.