DEPLETION OF NON-RESONANT IONIZATION

Abstract

Structured valleys in the multiphoton ionization spectrum of $CS_{2}$ at room temperature vapor pressure between 360nm and 390nm are assigned to the $X^{1}\Sigma^{+}_{g}-a^{3}A_{2}$ transition of $CS_{2}$. Absorption to the $a^{3}A_{2}$ state depletes levels of the around state which would otherwise have contributed to non-resonant ionization. In this manner, structured features resulting from an absorption to an excited state which does not ionize efficiently can be observed in multiphoton ionization spectra. Using a population rate equations treatment, the effects of non-resonant-ionization and collisional rethermalization on multiphoton ionization lineshapes lead to simple criteria for depletion of non-resonant ionization (DNRI). DNRI should be feasible for multiphoton absorptions and complement resonantly enhanced multiphoton ionization in cases where the latter is weak for reasons of geometry or short excited state lifetimes.