The near-threshold photoionization spectrum of aligned Ca 4s5p 1P1

The relative cross-section for photoionization from the 4s5p 1P1 excited level of neutral Calcium has been measured using pulsed-laser excitation and ionization of Ca atoms in an atomic beam. Both total and angle-differential spectra have been determined by recording photoelectrons as a function of ionizing photon energy and polarization and normalizing separate measurements to excited level fluorescence and ionizing laser pulse energy. Measurements cover the energy range from 1900 to 2400 cm-1 above the Ca+ 4s threshold at a resolution of approximately 0.1 cm-1. The shape and relative height of resonances corresponding to the previously identified 3S1 and 3D1,2 autoionizing levels from the 3d4d configuration have been determined. A new, extremely strong resonance is also evident at 2160 cm-1, and it has been tentatively identified as coming from an even 1P level