Inelastic collisions, between electrons of low and medium energies and
H2O molecules, that give rise to the appearance of optical radiation
were studied. An experiment was performed with a gas-filled cell using
an extended beam of monokinetic electrons to excite the molecules. A
spectrum appearing in the visible region was identified as belonging t
o H2O+. About 430 excitation cross sections attributed to 10 subbands
of the <(A)over tilde (2)A(1)> - <(X)over tilde B-2(1)> system were me
asured. For a number of lines, measurements were made of the optical e
xcitation functions in the range of energies from the excitation thres
hold to 200 eV.