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Updated: Nov 5, 2025

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
Published on: August 6, 2018
Ultrafast geometrical reorganization of a methane cation upon sudden ionization: an isotope effect on electronic
Cayo E M Gonçalves1, R D Levine2, F Remacle3
1Theoretical Physical Chemistry, University of Liège, 4000 Liège, Belgium. fremacle@uliege.be.
Abstract:
The ultrafast structural, Jahn-Teller (JT) driven, electronic coherence mediated quantum dynamics in the CH4+ and CD4+ cations that follows sudden ionization using an XUV attopulse exhibits a strong isotope effect. The JT effect makes the methane cation unstable in the Td geometry of the neutral molecule. Upon the sudden ionization the cation is produced in a coherent superposition of three electronic states that are strongly coupled and neither is in equilibrium with the nuclei. In the ground state of the cation the few femtosecond structural rearrangement leads first to a geometrically less distorted D2d minimum followed by a geometrical reorganization to a shallow C2v minimum. The dynamics is computed for an ensemble of 8000 ions randomly oriented with respect to the polarization of the XUV pulse. The ratio, about 3, of the CD4+ to CH4+ autocorrelation functions, is in agreement with experimental measurements of high harmonic spectra. The high value of the ratio is attributed to the faster electronic coherence dynamics in CH4+.
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