Abstract
Relative values of differential cross sections (DCS) are measured by the crossed-beam method. Two cylindrical-mirror energy analysers are employed. One of them is moved to detect scattered electrons at every angle, and the other is fixed at an angle to monitor the elastic scattering events. The effects of target gas distributions in a molecular beam flowing out from a multicapillary array are taken account of to correct the relative values. The DCS are also measured at an angle for water molecules and helium atoms by using gas chamber. On the basis of the absolute DCS for He measured by Jansen et al. (1976), the relative DCS for water molecules are converted into absolute values. In addition, the DCS are calculated by the partial-wave method for the double Yukawa potential. The values of its three adjustable parameters are determined by comparison with the experimental DCS. A spherically symmetric realistic potential is also inferred without adjustable parameters from the charge distribution that was derived from molecular-orbital theory. The DCS calculated for this potential reproduce the experimental values fairly well.