Abstract
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 $łeqsim$1 TW/cm2 to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O2+ production is found to be resonance enhanced around 400 nm via three-photon excitation to the e$'$3$Delta$u(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.
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@article{caballoDisentanglingMultiphotonIonization2023,
title = {Disentangling Multiphoton Ionization and Dissociation Channels in Molecular Oxygen Using Photoelectron\textendashPhotoion Coincidence Imaging},
author = {Ana Caballo and Anders J. T. M. Huits and David H. Parker and Daniel A. Horke},
url = {https://pubs.acs.org/doi/10.1021/acs.jpca.2c06707},
doi = {10.1021/acs.jpca.2c06707},
issn = {1089-5639, 1520-5215},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {J. Phys. Chem. A},
volume = {127},
number = {1},
pages = {92--98},
abstract = {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 $\leqsim$1 TW/cm2 to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O2+ production is found to be resonance enhanced around 400 nm via three-photon excitation to the e$'$3$Delta$u(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.},
keywords = {Coincidence Imaging, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},
pubstate = {published},
tppubtype = {article}
}