Experimental and theoretical total state-selected and state-to-state absolute cross sections. II. The Ar+(2P3/2,1/2)+H2 reaction

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Abstract
Total state‐selected and state‐to‐state absolute cross sections for the reactions Ar+(2P3/2,1/2)+H2(X,v=0)→Ar (1S0)+H+2(X̃,v’) [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(H+2)] reveal that at Ec.m.≤5 eV, σ1/2(H+2) is greater than σ3/2(H+2), while the reverse is observed at Ec.m.≥7 eV. The total state‐to‐state absolute cross sections for reaction (1) (σ3/2,1/2→v’) show unambiguously that in the Ec.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 H+2(X̃,v’=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 H+2(X̃,v’=0–4)+Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X3/2→v’[≡σ3/2→v’/σ3/2 (H+2)] 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(H+2). 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.

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