One- and two-photon detachment of the negative chlorine ion

Abstract
The authors report the first observation of tunable non-resonant two-photon photodetachment of an atomic negative ion and compare the two-photon detachment cross section of Cl- to the single-photon detachment one. In each case, Wigner law behaviour is observed, with s-wave detachment for the single-photon process and p-wave detachment for the two-photon process. The measured electron affinity of chlorine is 29 138.3 (5) cm-1, improving the precision of that number by more than an order of magnitude over previous measurements. The order of non-linearity of the two-photon detachment process appears to be less than two. Possible explanations for this anomaly are discussed.