A STATE-SELECTED STUDY OF THE ION-MOLECULE REACTIONS O-2,P-2)+H2O((D)

State-selected absolute cross sections for H2O+ and OH+ formed by the O+(D-2, P-2)+H2O reactions have been measured in the center-of-mass co llision energy (E(c.m.)) range of approximate to 0.10-30 eV. The charg e transfer cross sections for O+(D-2)+H2O are significantly higher tha n those for O+(S-4)+H2O. This observation is attributed to the increas ed number of accessible exothermic product channels for O+(D-2)+H2O. W hile the H2O+ cross sections for O+(P-2)+H2O are comparable to those f rom O+(S-4)+H2O at E(c.m.).greater than or equal to 1 eV, the H2O+ cro ss sections for O+(P-2)+H2O at E(c.m.) <1 eV are substantially lower t han those for O+(S-4)+H2O. The lower H2O+ cross sections observed for O+(P-2)+H2O are rationalized as due to further dissociation of excited charge transfer H2O+ ions and/or the efficient competition of the OH+OH product channel. The cross sections for OH+ from O+(D-2,P-2)+H2O a re significantly greater than those from O+(S-4)+H2O. The majority of OH+ ions from O+(D-2,P-2)+H2O are associated with exothermic channels corresponding to the formation OH+(X(3) Sigma(-),(1) Delta,A (3) Pi)+O H. The comparison of the sum (sigma(T)) of the cross sections for H2O and OH+ from O+(S-4)+H2O to those from O+(D-2)+H2O and O+(P-2)+H2O sh ows that sigma(T)'s for O+(S-4)+H2O and O+(P-2)+H2O are comparable, wh ereas the sigma(T) values for O+(D-2)+H2O are greater than those for O +(S-4)+H2O and O+(P-2)+H2O. The sigma(T) values are found to conform w ith the 1/E(c.m.) dependence at low E(c.m.)'s, indicating that the ion -dipole interaction plays an important role in the formation of the lo ng-lived collision complexes. The high cross sections for H2O+ and OH from O+(D-2,P-2)+H2O observed here suggest that these reactions shoul d be included in the simulation of the H2O+ and H3O+ ion density data obtained in 3 space-borne mass spectrometric experiments. (C) 1997 Ame rican Institute of Physics.