Fast ion-beam photoelectron spectroscopy of Ca-: Cross sections and asymmetry parameters

We have made a spectroscopic study of the electrons photodetached from a fast beam of Ca^- ions by laser photons of energy 2.08 eV. The spectrum exhibits peaks associated with detachment via the Ca(¹S)+e^-(ks,d) and the Ca(³P)+e^-(kp) channels. The measured angular dependence of electron yields in each peak has been used to determine asymmetry parameters. The results are β=1.21(4) and 1.60(4) for the ¹Sks,d and the ³Pkp channels, respectively. The measured saturation dependence of the electron yield on photon flux has been used to determine photodetachment cross sections for the same channels. The results are σ=66(7) and 61(5) Mb, respectively. The latter values disagree significantly with the only available calculation.