EXPERIMENTAL AND THEORETICAL TOTAL STATE-SELECTED AND STATE-TO-STATE ABSOLUTE CROSS-SECTIONS .1. THE H-2+(X,V')+AR REACTION

Total state-selected and state-to-state absolute cross sections for the reactions, H2+ (X̃,v′ = 0-4) + Ar→H 2(X,v) + Ar+ (2P3/2,1/2) [reaction (I)], ArH+ + H[reaction (II)], and H+ + H + Ar[reaction (III)], have been measured in the center-of-mass collision energy (E c.m.) range of 0.48-100 eV. Experimental state-selected cross sections for reactions (I) and (II) measured at Ec.m. = 0.48-0.95 eV are in agreement with those reported previously by Tanaka, Kato, and Koyano [J. Chem. Phys. 75, 4941 (1981)]. The experiment shows that prominent features of the cross sections for reactions (I) and (II) are governed by the close resonance of the H2+ (X̃,v′ = 2) + Ar and H2(X,v = 0) + Ar+ (2P1/2) vibronic states. At Ec.m. ≤3 eV, the vibrational state-selected cross section for the charge transfer reaction (I) is peaked at v′ = 2. The enhancement of the charge transfer cross section for v′ = 2 as compared to other v′ states of reactant H2+ increases as E c.m. is decreased. The state-to-state cross sections for reaction (I),measured at Ec.m. ≤3 eV, show that the enhancement for the charge transfer cross section for v′ = 2 is due to the preferential population of Ar+ (2P1/2). At Ec.m. = 0.48-0.95 eV and v′ = 2, nearly 80% of the charge transfer product Ar+ ions are formed in the 2P1/2 state. However, at Ec.m. > 5 eV, the intensity for charge transfer product Ar+ (2P3/2) is greater than that for Ar+ (2P1/2). Contrary to the strong vibrational dependence of the cross section for reaction (I), the cross section for reaction (II) is only weakly dependent on the vibrational state of H 2+. At Ec.m. ≤3 eV, the cross section for the formation of ArH+ is the lowest for v′ = 2 compared to other v′ states, an observation attributed to the competition of the nearly resonant Ar+ (2P1/2) + H2(X,v = 0) charge transfer channel. The cross section for reaction (II) decreases with increasing Ec.m.. At Ec.m. ≥20 eV, the cross sections for the formation of ArH+ become negligible compared to those for Ar+. The appearance energies for the collision-induced dissociation H2+ (X̃,v′ = 0-4) are consistent with the thermochemical threshold for reaction (III). The cross sections the formation of H+ are ≤20% of those for H2+. Theoretical state-to-state cross sections for reaction (I) at Ec.m. = 19.3 and 47.6 eV calculated using the nonreactive infinite-order sudden approximation are found to be in fair agreement with experimental results. © 1990 American Institute of Physics.