Close-coupling optical model analysis: A refined optical potential surface for He*(2 1S)+H2

A complex-arithmetic version of Johnson’s log–derivative integration method has enabled a straightforward extension of the close-coupling approximation to complex-potential surfaces. The complex-potential close-coupling (CPCC) method is applied to the determination from our earlier scattering measurements of an improved anisotropic optical potential for the He*(2 1S)+H2 Penning ionization system, with the aid of a new, nonpiecewise potential surface function based on the improved Tang–Toennies model. The potential is compared to earlier ab initio results, and the CPCC method is used to assess the shortcomings of the complex-infinite-order-sudden (CIOS) approximation. Variation of differential and ionization cross sections with the initial rotational state of H2 predicted by CPCC may be experimentally observable, and may also provide an explanation for the observed H2/D2 isotope effect in quenching rates.