| The fundamentally important process of associative ionization (AI), A + B → AB+ + e-, was studied in collisions between laser-excited sodium atoms in a crossed-beam apparatus. The absolute rate constant for AI in collisions between two Na(3p) atoms was determined. For the first time, the effects of radiation trapping, Doppler broadening, and hyperfine splitting on the measurement of the rate constant for this process have been rigorously treated. The measured rate constant is (1.1 +/- 0.4) x 10-11 cm3/sec, which corresponds to a velocity averaged cross section of ≈0.9 A2. Associative ionization in collisions between Na*(np) levels and the Na(3s) ground state was investigated. The absolute rate constants for AI, measured for principal quantum numbers ranging from n = 5--15, exhibit a pronounced dependence on n, with a maximum of approximately 3 x 10-9 cm3/sec near n = 11. Comparisons are made with the theoretical model developed by Duman and Shmatov, and Janev and Mihajlov. Laser photodissociation of the sodium ion dimers has been used to increase our understanding of the dynamics of the AI process. Through time-of-flight energy analysis of the ionic photofragments, the vibrational manifold populated in the AI process was determined. We find that while all energetically accessible v″ levels are populated, the maximum corresponds to collisions which occur at the most probable relative collision energy, with ejection of low or zero kinetic energy electrons. We have measured the total photodissociation cross section over the wavelength region of 4650 ≤ lambda ≤ 5350 A, and found that it varies between 10-17 and 10 -16 cm2. |
