Observing Phase Space Evolution During Unimolecular Decay
Abstract
Direct time-resolved observation of large amplitude dynamics during ground state statistical unimolecular decay remains an experimental challenge. Here, an experimental Time-Resolved Coulomb Explosion Imaging (TR-CEI) study (J. Chem. Phys. 151, 174301, 2019) of the canonical unimolecular reaction NO2 → NO(2Π, v=0, J) + O(3Pj) at threshold dissociation energies is modeled and analyzed. Quasi-classical trajectory (QCT) simulations on an accurate and validated ground state potential energy surface (PES), with energy and angular momentum constraints from known product state distributions, are used to characterize the dissociation dynamics. TR-CEI projects suddenly, via ultrafast Strong Field Ionization (SFI), the evolving neutral ground state wavepacket onto the repulsive doubly charged cationic state which then impulsively fragments into the NO+ + O+ ion pair. Within the Coulomb recoil approximation, which applies at longer NO--O (Jacobi) separations, the ion pair CEI-energy is inversely proportional to the scalar distance between the neutral ground state NO and O moieties at the moment of SFI, thus providing a direct measure of the evolving average NO--O distance during unimolecular decay. Results from QCT simulations agree favourably with the TR-CEI measurements. Phase space evolution, recurrence time distributions and Lyapunov exponent analysis are presented which support the conclusion that TR-CEI directly observes phase space evolution during unimolecular decay. For the present system, the time scale for the phase space distribution to achieve statisticality is estimated to be 2 to 3 ps.
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BibTeX
@misc{vijayakumar2026observing,
title = {{Observing Phase Space Evolution During Unimolecular Decay}},
author = {Abhirami Vijayakumar and Raidel Martin Barrios and Meenu Upadhyay and JingChun Wang and Andre Staudte and Albert Stolow and Markus Meuwly},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30869},
eprint = {2609.30869},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30869},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Observing Phase Space Evolution During Unimolecular Decay
AU - Abhirami Vijayakumar
AU - Raidel Martin Barrios
AU - Meenu Upadhyay
AU - JingChun Wang
AU - Andre Staudte
AU - Albert Stolow
AU - Markus Meuwly
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.30869
UR - https://arxiv.org/abs/2609.30869
AB - Direct time-resolved observation of large amplitude dynamics during ground state statistical unimolecular decay remains an experimental challenge. Here, an experimental Time-Resolved Coulomb Explosion Imaging (TR-CEI) study (J. Chem. Phys. 151, 174301, 2019) of the canonical unimolecular reaction NO_2 → NO(^2Π, v=0, J) + O(^3P_j) at threshold dissociation energies is modeled and analyzed. Quasi-classical trajectory (QCT) simulations on an accurate and validated ground state potential energy surface (PES), with energy and angular momentum constraints from known product state distributions, are used to characterize the dissociation dynamics. TR-CEI projects suddenly, via ultrafast Strong Field Ionization (SFI), the evolving neutral ground state wavepacket onto the repulsive doubly charged cationic state which then impulsively fragments into the NO^+ + O^+ ion pair. Within the Coulomb recoil approximation, which applies at longer NO--O (Jacobi) separations, the ion pair CEI-energy is inversely proportional to the scalar distance between the neutral ground state NO and O moieties at the moment of SFI, thus providing a direct measure of the evolving average NO--O distance during unimolecular decay. Results from QCT simulations agree favourably with the TR-CEI measurements. Phase space evolution, recurrence time distributions and Lyapunov exponent analysis are presented which support the conclusion that TR-CEI directly observes phase space evolution during unimolecular decay. For the present system, the time scale for the phase space distribution to achieve statisticality is estimated to be 2 to 3 ps.
ER -