High-resolution threshold photodetachment spectroscopy of OH

Relative photodetachment cross sections for rotational thresholds of the hydroxide anion were measured using a coaxial laser-ion beam spectrometer. The thresholds correspond to transitions from the J51 and J52 states of X S OH to the J53/2 state of X P3/2 OH. Best fits of the data give cross sections that scale with energy above threshold as (E2E th) 0.1860.06 and (E2E th) 0.2160.05 for the two thresholds, respectively. This non-Wigner law energy dependence of the cross section results from the long-range r interaction between the dipole and the departing electron. Experimental results were compared with the predictions of a strong-coupling model of charge-dipole interaction devised by Engelking and good qualitative agreement was observed. When the resolution and range of the data for transitions that terminate in the lower L-doublet component is such that the L-doublet splitting is resolved, one observes the (E2E th) 1/2 behavior predicted by the Wigner law. This result is explained in terms of the effect of the L doubling upon the r charge-dipole interaction. From the threshold frequencies, an OH electron affinity of 14 741.02~3! cm was determined. @S1050-2947~97!04803-8#