Resolution of a discrepancy in elastic electron scattering from water

The 2008/2012 measurements of Khakoo et al., and the 2004 measurements of Cho et al. of elastic electron scattering from water, both employing the well known relative flow method (RFM), showed variation beyond the limits of their error bars. Khakoo et al. employed an aperture gas collimator instead of the standard capillary, an approach designed to remove any physical assumption about water's gas diameter from the RFM. They hypothesized that the differences were the result of Cho et al. employing an unsuitable estimate of the gas diameter. However, the data of Cho et al. agrees better with modern quantum chemical calculations, which is curious if their approach was systematically flawed. This discrepancy is important as water plays a vital role in the chemistry of biological environments.

We present measurements of the elastic DCS of water, at electron energies between 10 - 50eV, using a tube based setup similar to that of Cho et al, but measuring the cross section as a function of the assumed gas diameter and the reservior pressure behind the gas collimator. The data will be used to assess the sensitivity of relative flow measurements to the physical assumptions behind them, and to resolve whether Khakoo et al.'s data are indeed a systematic improvement over previous results.