Photodetachment of Electrons from SH−

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Abstract
The cross section for photodetechment of electrons from SH− for the first 0.75 eV above threshold (λ = 534.7 to 403.0 nm) has been measured in a crossed-beam experiment. The cross section rises rapidly in the first 0.15 eV (Δλ = 35 nm) to the value 1.9 × 10−17 cm2 determined with a total uncertainty of ± 0.4 × 10−17 cm2 given by the square root of the sum of the squares of the maximum observed deviation and the allowances for various systematic factors; over the rest of the observed range it is constant. The detailed shape of the cross section vs λ curve has been employed to derive the SH− structural parameters (and their upper limits of uncertainty), which are indistinguishable from those of the neutral free radical: R = 0.135 ± 0.002 nm, ωe = 2700 ± 300 cm−1, and Be = 9.46 ± 0.32 cm−1. The electron affinity is identified with the observed photodetechment threshold, 2.319 ± 0.010 eV. These results are in general agreement with the recent calculations of Cade. Evidence is presented for the importance of inclusion of long-range forces in dealing with the threshold behavior of photodetechment from heteronuclear diatomic negative ions.