Vibrational-excitation cross sections of water molecules by electron impact

Absolute differential cross sections for vibrational excitation of water-vapor molecules are measured by use of a crossed-beam method. The energy and angular range were from 2.2 to 20 eV and from 30^∘{} to 150^∘{}, respectively. Vibrational-excitation cross sections were measured for the bending (010) and stretching (100) and (001) modes of the electronic ground state. A broad resonance for the stretching modes near 6-eV impact energy was observed. The present results generally agree in angular distribution with the measurements by G. Seng and F. Linder [J. Phys. B. 9, 2539 (1976)], except below 30^∘{} scattering angle. However, the integral cross sections agree within experimental uncertainty. The theoretical results of A. Jain and D. G. Thompson [J. Phys. B 16, L347 (1983)] for the bending mode are in good agreement with the present results. These new results have implications for theoretical modeling of cometary ionospheres.