An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the “trap loss” technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs $6{}^2{P}_{3∕2}$ state between $7\mathrm{eV}$ and $400\mathrm{eV}$. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region $(<11\mathrm{eV})$ where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

Excitation and fluorescence ultraviolet spectra of ${\mathrm{Cd}}_2$ recorded at the ${}^1{0}_u^{+}\left(5\mathrm{}{}^1{P}_1\right)–X{}^1{0}_g^{+}$ transition are reported. The ${\mathrm{Cd}}_2$ molecules (seeded in Ar) produced in a continuous free-jet supersonic beam were excited in a vacuum chamber with a pulsed dye-laser beam. A well-resolved vibrational structure of the ${}^1{0}_u^{+}\leftarrow X{}^1{0}_g^{+}$ excitation spectrum as well as the isotopic structure of the vibrational components were recorded. Analysis of the spectrum yielded vibrational constants for the ${}^1{0}_u^{+}$ state: ${\omega }_e^{\prime }=100.50\mathrm{}\pm 0.25{\mathrm{cm}}^{-1},$ ${\omega }_e^{\prime }{x}_e^{\prime }=0.325\mathrm{}\pm 0.003{\mathrm{cm}}^{-1},$ $D_0^{\prime }=8638\mathrm{}\pm 15{\mathrm{cm}}^{-1},$ $D_e^{\prime }=8688\mathrm{}\pm 15{\mathrm{cm}}^{-1},$ and $\Delta R_e{=R}_e^{″}-R_e^{\prime }=1.04\mathrm{}\pm 0.01\AA$ derived for the ${}^{226}{\mathrm{Cd}}_2$ isotopomer. The ${}^1{0}_u^{+}$ state potential-energy (PE) curve was obtained numerically using an inverse perturbation approach (IPA) procedure. Condon internal diffraction (CID) patterns in the ${}^1{0}_u^{+}\to X{}^1{0}_g^{+}$ fluorescence band, emitted upon the selective excitation of the $v^{\prime }=38\mathrm{}$ and $v^{\prime }=39\mathrm{}$ vibrational components of the ${}^{226}{\mathrm{Cd}}_2$ isotopomer, were observed and improved the $v^{\prime }$ assignments derived from the analysis of the isotopic structure. Analysis of the fluorescence spectrum yielded information on the repulsive part of the ground-state interatomic potential. The result confirms a relatively soft repulsion between two Cd atoms in the short-range (2.53–4.05 Å) region and makes allowance for a covalent admixture to the ground-state van der Waals bonding. Quasirelativistic valence ab initio calculations on the PE curves for the investigated states have been performed at the complete-active-space multiconfiguration self-consistent-field (CASSCF/CAS) multireference second-order perturbation theory (CASPT2) level with the total of 40 correlated electrons. In the calculations, the Cd atom is considered as a 20-valence electron system whereas the ${\mathrm{Cd}}^{20+}$ core is replaced by an energy-consistent pseudopotential which also accounts for scalar-relativistic effects and spin-orbit interaction within the valence shell. A comparison with results obtained from other experiments and ab initio calculations is presented.