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Updated: May 31, 2026

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
Published on: August 6, 2018
Communication: A new spectroscopic window on hydroxyl radicals using UV + VUV resonant ionization
Joseph M Beames1, Fang Liu, Marsha I Lester
1Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Abstract:
A 1 + 1' multiphoton ionization (MPI) detection scheme for OH radicals is presented. The spectroscopic approach combines initial excitation on the well-characterized A(2)Σ(+)-X(2)Π band system with vacuum ultraviolet (VUV) ionization via autoionizing Rydberg states that converge on the OH(+) A(3)Π ion state. Jet-cooled MPI spectra on the (1,0) and (2,0) bands show anomalous rotational line intensities, while initial excitation on the (0,0) band does not lead to detectable OH(+) ions. The onset of ionization with the (1,0) band is attributed to an energetic threshold; the combined UV + VUV photon energies are above the first member of the autoionizing (A(3)Π)nd Rydberg series. Comparison of the OH 1 + 1' MPI signal with that from single photon VUV ionization of NO indicates that the cross section for photoionization from OH A(2)Σ(+), v' = 1 is on the order of 10(-17) cm(2).
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