RESONANT 2 PHOTON IONIZATION OF V-ATOMS - V+ ELECTRONIC STATE DISTRIBUTIONS AND J-RESOLVED PHOTOELECTRON ANGULAR-DISTRIBUTIONS

We use one color, resonant two photon absorption to ionize a skimmed atomic beam of V formed by laser vaporization of a target rod in the throat of a pulsed nozzle. The resulting time-of-flight photoelectron spectra resolve the 3d4(5D), 3d34s(5F), and 3d 34S(3F) electronic terms and the spin-orbit levels J = 2, 3, and 4 within 3d 34s(3F) as well. For nine different ionizing wavelengths, we present state-resolved photoelectron angular distributions, which yield anisotropy coefficients β2,i and β4,i and angle-integrated electronic branching fractions f i for each resolved feature i. Generally speaking, the photoionization cross sections are dominated by direct processes of the type 3d3(4F)4s4p(1P0) → 3d 34s(3,5F) + ks,kd whenever the leading term in the intermediate state wave function and the total available energy permit. All of the corresponding term-resolved angular distributions are qualitatively similar, with positive β2 and negligible β4. When the leading term of the intermediate state is of the form 3d3( 2X) 4s4p(3P0), where X is the orbital angular momentum of the 3d3 core, the V+ branching fractions are not easily understood. In these cases of indirect ionization, term-resolved angular distributions are typically nearly isotropic. We find no clear evidence of nonzero β4 parameters. The J-specific angular distributions vary substantially for J = 2, 3, and 4 within the 3d 34s( 3F) term. The branching fractions at each ionizing wavelength permit us to extract state-specific chemical reaction cross sections of V+ in the accompanying paper. © 1990 American Institute of Physics.