ABSOLUTE PARTIAL CROSS-SECTIONS FOR ELECTRON-IMPACT IONIZATION OF H2OAND D2O FROM THRESHOLD TO 1000 EV

Absolute partial cross sections for electron-impact ionization of H2O and D2O are reported for electron energies from threshold to 1000 eV. Data are presented for the production of H2O+ + OH+ + O+, O2+, H-2(+) and H+ from H2O and for the production of D2O+, OD+, O+, O2+, D-2(+), and D+ from D2O. The product ions are mass analyzed using a time-of-fl ight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are completely collec ted. The overall uncertainty in the absolute cross section values is /- 4.5% for singly charged parent ions and is slightly greater for fra gment ions. The cross sections for H2O and D2O are found to be the sam e to within experimental uncertainties except for the H, cross section which is approximately a factor of 2 greater than the D-2(+) cross se ction. Previous results are compared to the present measurements. (C) 1998 American Institute of Physics.