Abstract

Quantitative measurement of the competition between predissociation and photoionization of ${\text{O}}_2{\text{B}}^3{\Sigma }_u^{-}$ has been used to make the first determination of the two-photon ionization cross section at 193 nm of O₂ $\left(X^3{\Sigma }_g^{-}\right)$ Our investigation consisted of (1) photofragmentation of O₂ with an ArF* excimer laser (τ_pulse ~ 10 ns, I ~ 10¹⁰ W/cm²) to produce O (by one-photon dissociation) and ${\text{O}}_2^{+}$ (by two-photon ionization) fragments (see Fig. 1) and (2) making a quantum-defect calculation of the three-photon ionization cross section of O at 193 nm. The ionization and dissociation channels were distinguished by measuring the kinetic energy spectrum of O⁺ with a time-of-flight (TOF) ion detector that had an energy resolution of 0.1 eV, and the relative strengths of the two channels were determined by measuring the relative yields of O⁺ and ${\text{O}}_2^{+}$.

© 1993 Optical Society of America