EXPERIMENTAL AND THEORETICAL TOTAL STATE-SELECTED AND STATE-TO-STATE ABSOLUTE CROSS-SECTIONS .2. THE AR+(2P3/2,1/2)+H-2 REACTION

Total state-selected and state-to-state absolute cross sections for the reactions Ar+ (2P3/2,1/2) + H2(X,v= 0) →Ar( 1S0 ) + H2+ (X,õ') [reaction (1)], ArH+ + H [reaction (2) ], and H + + H + Ar [reaction (3) ] have been measured in the center-of-mass collision energy Ec.m range of 0.24-19.1 eV. Absolute spin-orbit state transition total cross sections (σ3/2→1/2 ,σ1/2→3/2 ) for the collisions of Ar+ ( 2P3/2,1/2 ) with H2 at Ec.m. = 1.2-19.1 eV have been obtained. The measured state-selected cross sections for reaction ( 1 ) [σ3/2,1/2 (H2+ ) ] reveal that at Ec.m ≤5 eV, σ1/2 (H2 + ) is greater than σ3/2(H2+ ), while the reverse is observed at Ec.m. ≥7 eV. The total state-to-state absolute cross sections for reaction ( 1 ) (σ 3/2,1/2→v′ ) show unambiguously that in the E c.m. range of 0.16-3.9 eV the dominant product channel formed in the reaction of Ar+ (2P1/2 ) + H2(X,v = 0) is H2+ (X̃v = 2) + Ar. These observations support the conclusion that at low Ec.m. the outcome of charge transfer collisions is governed mostly by the close energy resonance effect. However, at sufficiently high Ec.m. ( > 6 eV) the charge transfer of Ar + (2P3/2 ) + H2 is favored compared to that of Ar+ (2P1/2 ) + H2. The relative values measured for X1/2→v′ [ ≡σ1/2→v′/σ1/2(H 2+) ] are in good accord with those predicted from calculations using the state-to-state cross sections for the H2 + (X̃v′ = 0-4) + Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X 3/2→v′ [ ≡σ3/2→v′/ σ3/2(H2+) ] and those predicted using the microscopic reversibility argument are also in fair agreement. The spin-orbit effect for the cross section of reaction (2) [σ3/2,1/2(ArH + ) ] is significantly less than that for reaction ( 1 ). Both σ3/2 (ArH + ) and σ1/2 (ArH + ) decrease rapidly as Ec.m. is increased, and become essentially identical at Ec.m. ≈ 3.8 eV. The cross sections for reaction (3) observed in the Ec.m. range of 2.5-12 eV are ≤3% of σ3/2,1/2 (H2+ ). The onset for the formation of H + by reaction (3) is consistent with the thermochemical threshold. The values for σ3/2→1/2 and σ1/2→3/2 observed here are nearly a factor of 2 greater than those measured by the energy loss spectroscopic method. However, the kinetic energy dependencies for σ3/2→1/2 and σ1/2→3/2 are in accord with the previous measurements. Theoretical cross sections for the charge transfer and spin-orbit state transition reactions are calculated at Ec.m. = 19.3 eV using the nonreactive infinite-order sudden approximation for comparison with experimental values. © 1990 American Institute of Physics.