Photoelectron Spectroscopy of the Low Energy States of SmO+ and GdO.

Associative ionization reactions of the type Ln + O → LnO+ + e- (where Ln is a lanthanide) are being investigated as they may be used to transiently modify local electron densities at high altitudes. The most promising elements are those for which the LnO bond dissociation energy (BDE) exceeds the LnO ionization energy (IE). Consequently, accurate measurements of the BDE's and IE's are needed for the identification of exothermic associative ionization reactions. Sounding rocket experiments have been carried out for releases of thermally vaporized Sm. Emission spectroscopy was used as a diagnostic for the Sm + O reaction. It was hoped that the degree of ionization could be deduced from emission spectra, but the analysis has been inconclusive due to the lack of spectroscopic data for SmO+. In the present study we have mapped the low energy states of SmO+ using pulsed field ionization─zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. The data obtained are suitable for use in the analyses of the overlapped SmO/SmO+ spectra. The Gd + O → GdO+ + e- reaction is known to be exothermic, but a wide range of values for the IE have been reported from both experimental observations and theoretical calculations. In the present study PFI-ZEKE measurements have been used to establish a more accurate IE (6.075 ± 0.001 eV) and the vibrational frequency for the GdO+ ground state.