Rydberg electron transfer to hydrogen iodide: Dissociative and nondissociative electron capture

Abstract

Rydberg electron transfer (RET) to jet-cooled hydrogen iodide (HI) molecules has been studied for alkali atoms excited to ns and nd Rydberg levels (9<n<40). I− ions produced by dissociative electron capture are observed for all Rydberg levels studied, even though dissociative RET becomes endothermic for n<52. For n≳23, rate constants for I− formation are in good agreement with previous results for low energy free electron attachment. For lower values of n, the RET results deviate from the free electron results due to electrostatic interactions between the nascent positive (Rydberg core) and negative ions. A simple calculation based upon the ‘‘free electron model’’ agrees quantitatively with the rate constant data for n≳13. For Rydberg levels with n<13, long-lived HI− (and DI−) ions are observed which appear to be stable with respect to both dissociation and autodetachment. These observations indicate that a bound and stable anion state exists, correlating with the lowest H(D)+I− limit, with a potential well which supports at least one vibrational level for both HI− and DI−.