zhao_2023#

X. Zhao, T. Xu, X. Yu, D. Ren, M. Li, X. Zhang, X. Li, P. Ma, D. Zhang, C. Wang, Q. Wang, X. Hu, S. Luo, Y. Wu, J. Wang and D. Ding, “Probing electron localization during molecular dissociation by femtosecond strong-field ion momentum spectroscopy”, Commun. Phys. 6, 124 (2023)

Source record · Catalogue · Review register

DOI: 10.1038/s42005-023-01248-3

Source kind: measurement

Recorded technique: Strong-field pump, strong-field probe ion momentum spectroscopy of N2O in a COLTRIMS (16.9 V/cm extraction, delay-line detector): an 800 nm, ~35 fs pump, linear, 1.0 x 10^14 W/cm2, ionises N2O to N2O+ (B 2Pi); an elliptical probe (epsilon ~ 0.7, 3.5 x 10^14 W/cm2) ionises the dissociating cation to N2O2+, and the coincident NO+ + N+ and N2+ + O+ pairs give the kinetic energy release against delay (to 6 ps; cross-correlation 90 fs FWHM). Semiclassical Landau-Zener surface-hopping trajectories on CASSCF potential surfaces for comparison (Methods, p. 6).

Materials in structured entries: N2O

Dataset quantities: dissociation_time, kinetic_energy_release

Contents: 6 datasets; 0 formulas.

Curation notes#

Commun. Phys. 6:124 (2023), pdf pages 1-7. Identity checked on pdf page 1 (title, authors, ‘(2023) 6:124’, DOI). Same group and apparatus as zhao_2020. The supplementary information (Supplementary Notes 1-3, Figs. 1-4: the rise times of the two channels, the trajectories) is not in the library.

THE MEASUREMENT AND ITS KER (pp. 2-4; TC-971). The probe’s Coulomb explosion KER of the dissociating cation is KER(t) = E0 + E_cou(t), E_cou = 1/R(t) (atomic units), with E0 ‘the initial KER from the dissociation of the B 2Pi state’ (p. 3). One branch of the coincident KER is constant (direct double ionisation by one pulse); the other falls ‘to asymptotic energies of 0.6 eV for the NO+ + N+ channel and 0.4 eV for the NN+ + O+ channel at a delay time of 6 ps’ (p. 3); the simulation gives 1.1 eV and 0.5 eV, the difference ascribed to the neglect of the fragments’ vibrational and rotational energy (pp. 3-4). ‘Both the experiments and simulations demonstrate that the KER decreases rapidly in the first ps ... The KER reaches the dissociation energy for both channels at around 1 ps, suggesting that the ultrafast dissociation of both channels is complete within the first ps’ (pp. 3-4). Selection windows: 0.5-5.0 eV (NO+ + N+), 0.3-4.6 eV (NN+ + O+) (p. 2).

DOUBT (TC-971): the 6 ps value includes the residual Coulomb energy 1/R at the probe; the paper gives R = 140 a.u. at 1500 fs for N-NO+ (p. 4), where 1/R is 0.19 eV, and R at 6 ps is not stated, so the asymptotes are upper bounds to E0 by an amount not given. No uncertainty is printed.

STATE ASSIGNMENTS (pp. 2-4): the pump populates B 2Pi, most likely by tunnelling from HOMO-1 to A 2Sigma+ followed by excitation within the pulse (HOMO-2 negligible); B 2Pi couples through conical intersections to 2Delta states and dissociates to NO+ + N(2D) (2pi -> 8sigma) or NN+ + O(3P) (7sigma -> 3pi) (Fig. 2, p. 4).

NOT TAKEN: the asymmetries of the ion sum momentum (Figs. 1, 4), which carry the paper’s electron-localisation result; the calculated dipole-moment differences (Fig. 4c, d). Figures for later (TC-971): Fig. 3(a, c), the measured KER against delay (raster maps with vector axes), for the time dependence; Fig. 1(c, f) (vector).

Recorded bibliographic identity status: VALIDATED. This concerns identification of the source; it does not establish the scientific correctness of its contents.