ABSOLUTE STATE-SELECTED TOTAL CROSS-SECTIONS FOR THE ION-MOLECULE REACTIONS O-4,D-2,P-2)+H-2(D-2)((S)

Absolute total cross sections for the state-selected reactions of O+(S -4,D-2,P-2) + H-2 (D-2) have been measured in the center-of-mass colli sion energy (E(c.m.)) range of 0.02-12 eV. The cross sections for OH(OD+) from O+(D-2)+H-2(D-2) are slightly higher than those from O+(S-4 )+H-2(D-2), whereas the OH+ (OD+) cross sections from O+ (P-2)+H-2(D-2 ) are approximate to 40% lower than those from O+(S-4)+H-2 (D-2) and O + (D-2) + H-2 (D-2). At E(c.m.) <0.5 eV, the total cross sections for OH+ (OD+) from O+ (S-4)+H-2 (D-2) and O+(D-2)+H-2 (D-2) are in accord with those predicted by the Langevin-Gioumousis-Stevenson model. Signi ficantly higher cross sections are observed for H+ (D+) and H-2(+) (D- 2(+)) from O+(D-2)+H-2 (D-2) and O+(P-2)+H-2 (D-2), as compared to tho se from O+(S-4)+H-2 (D-2). The exothermic nature of the O+(D-2, P-2) H-2 (D-2) charge transfer collisions accounts for the high cross sect ions are identified with the H+ (D+)+O+H channel, the H+ (D+) ions fro m the reactions involving O+(D-2) and O+(P-2) are associated mostly wi th the H+ (D+)+OH(OD) channel, the formation of which obeys the spin-c onservation rule. The comparison of the sum (sigma(T)) of cross sectio ns for OH+ (OD+), H-2(+) (D-2(+)), and H+ (D+) from O+(S-4)+H-2(D-2) t o those from O+(D-2)+H-2(D-2) and O+(P-2)+H-2 (D-2) shows that the sig ma(T)s for O+(S-4)+H-2(D-2), O+(D-2)+H-2(D-2), and O+(P-2)+H-2(D-2) at E(c.m.) <0.5 eV are comparable. At E(c.m.)>0.5 eV, the sigma(T)s for O+(P-2)+H-2 (D-2) are greater than those for O+(D-2)+H-2 (D-2), which in turn are greater than those for O+(S-4)+H-2 (D-2). This observation is attributed to the increase in the number of accessible product cha nnels for reactions involving the excited O+(D-2) and O+(P-2) reactant ions. (C) 1997 American Institute of Physics.