Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Laser photoionization studies of excited atomic states of titanium and calcium
Abstract
Photoionization cross sections from excited states of titanium and calcium have been measured using pulsed-laser excitation and ionization of atomic beams of the respective elements. Absolute cross sections from the 3d$\sp2$4s4p $\sp3$P$\sb2$ excited level of Ti were obtained by assessing the depletion m excited state fluorescence due to ionization. This novel method does not require an atomic number density determination or saturation of the ionizing transition and is independent of particle detection efficiencies. The relative cross section for photoionizing the 4s5p $\sp1$P excited state of calcium was measured from 2000 to 2400 $cm\sp{-1}$ above threshold at a resolution of 0.15 $cm\sp{-1}$. The profiles for the 3d4d $\sp3$S and $\sp3$D$\sb{1,2}$ autoionizing resonances were assessed along with a new, extremely strong resonance at 2167 $cm\sp{-1}$. The dependence on the polarization state of the radiation employed to excite this new resonance allowed the assignment 3d4d $\sp1$P. This represents the first experimental identification of a doubly-excited, even-parity singlet level in calcium. Photoelectron angular distributions in the vicinity ofthe new resonance agreed with the total angular momentum $J=1$ assignment. The ratio for the radial dipole matrix elements for the photoelectron s- to d-wave production and the relative phase difference between these matrix elements were evaluated from angular distributions remote from the resonance structures. The ratio ofthe matrix elements was independent of energy within the relative standard deviation of 5% for the assessments; however, the relative phase difference showed a significant decrease with increasing ionizing energy even within the small region ofthe spectrum studied. The relative yields of Ca$\sp+$ and Ca$\sp-$ from intrabeam collisions between excited Ca 4snd $\sp1$D Rydberg atoms and ground-state calcium were measured as a function of n. A 25-fold increase in Ca$\sp+$ and Ca$\sp-$ production was observed for $n=25$ only. Based on the interpretation that such an enhancement occurs at resonance for the binding energy of the transferred electron, the electron affinity of calcium was assessed at $23.9\pm1.0$ meV.
Subject Area
Atoms & subatomic particles
Recommended Citation
McLaughlin, Kenneth Woot, "Laser photoionization studies of excited atomic states of titanium and calcium" (1995). ETD collection for University of Nebraska-Lincoln. AAI9600745.
https://digitalcommons.unl.edu/dissertations/AAI9600745