Disentangling Multiphoton Ionization and Dissociation Channels in Molecular Oxygen Using Photoelectron–Photoion Coincidence Imaging

Multiphoton excitation of molecular oxygen in the 392–408 nm region is studied using a tunable femtosecond laser coupled with a double velocity map imaging photoelectron–photoion coincidence spectrometer. The laser intensity is held at ≤∼1 TW/cm2 to ensure excitation in the perturbative regime, wher...

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Veröffentlicht in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2023-01, Vol.127 (1), p.92-98
Hauptverfasser: Caballo, Ana, Huits, Anders J. T. M., Parker, David H., Horke, Daniel A.
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Sprache:eng
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Zusammenfassung:Multiphoton excitation of molecular oxygen in the 392–408 nm region is studied using a tunable femtosecond laser coupled with a double velocity map imaging photoelectron–photoion coincidence spectrometer. The laser intensity is held at ≤∼1 TW/cm2 to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O2 + production is found to be resonance enhanced around 400 nm via three-photon excitation to the e′3Δu(v = 0) state, similar to results from REMPI studies using nanosecond dye lasers. O+ production reaches 7% of the total ion yield around 405 nm due to two processes: autoionization following five-photon excitation of O2, producing O2 +(X­(v)) in a wide range of vibrational states followed by two- or three-photon dissociation, or six-photon excitation to a superexcited O2** state followed by neutral dissociation and subsequent ionization of the electronically excited O atom. Coincidence detection is shown to be crucial in identifying these competing pathways.
ISSN:1089-5639
1520-5215
1520-5215
DOI:10.1021/acs.jpca.2c06707