By using the multiconfiguration time-dependent (TD) Hartree-Fock (MCTDHF) method, we simulated the multielectron dynamics of a CO molecule irradiated by near-IR two-cycle pulses with different ...carrier envelope phases. The ionization rate calculated is higher when the laser electric field ε(t) points from the nucleus C to O than the opposite case, in agreement with the results of two-color ionization experiments. The mechanism of anisotropic tunnel ionization in CO was examined by converting the obtained multielectron dynamics to the representation in terms of TD natural orbitals {ϕj(t)}. Within the framework of MCTDHF, we derived the unitary equations of motion for {ϕj(t)}. From the derived equations, we defined the TD effective potentials {υjeff(t)}that govern the dynamics of {ϕj(t)}. In υ5σeff(t)for the 5σ HOMO, a narrow hump that originates from two-body electron-electron repulsion is formed on the top of the field-induced distorted barrier near the nucleus C when ε(t) points from C to O, which is responsible for the directional anisotropy of tunnel ionization. For 4σ HOMO-2, a high barrier to suppress ionization is formed in υ4σeff(t)when ε(t) points from C to O, in correlation with the electron-electron interaction with a 5σ electron on route to ionization. For the opposite phase, υ4σeff(t)becomes barrierless, which enhances high-harmonic generation through ϕ4σ(t).
In situ femtosecond x-ray diffraction measurements and ab initio molecular dynamics simulations were performed to study the liquid structure of tantalum shock released from several hundred ...gigapascals (GPa) on the nanosecond timescale. The results show that the internal negative pressure applied to the liquid tantalum reached -5.6 (0.8) GPa, suggesting the existence of a liquid-gas mixing state due to cavitation. This is the first direct evidence to prove the classical nucleation theory which predicts that liquids with high surface tension can support GPa regime tensile stress.
Understanding x-ray radiation damage is a crucial issue for both medical applications of x rays and x-ray free-electron-laser (XFEL) science aimed at molecular imaging. Decrypting the charge and ...fragmentation dynamics of nucleobases, the smallest units of a macro-biomolecule, contributes to a bottom-up understanding of the damage via cascades of phenomena following x-ray exposure. We investigate experimentally and by numerical simulations the ultrafast radiation damage induced on a nucleobase analogue (5-iodouracil) by an ultrashort (10 fs) high-intensity radiation pulse generated by XFEL at SPring-8 Angstrom Compact free electron Laser (SACLA). The present study elucidates a plausible underlying radiosensitizing mechanism of 5-iodouracil. This mechanism is independent of the exact composition of 5-iodouracil and thus relevant to other such radiosensitizers. Furthermore, we found that despite a rapid increase of the net molecular charge in the presence of iodine, and of the ultrafast release of hydrogen, the other atoms are almost frozen within the 10-fs duration of the exposure. This validates single-shot molecular imaging as a consistent approach, provided the radiation pulse used is brief enough.
Liquid chalcogen-halogen A
2
X
2
(A: S, Se, X: Cl, Br) is a racemic mixture of enantiomers between left-handed (L) and right-handed (D) chiral molecules. The lone-pair orbital of the chalcogen atom ...significantly affects the molecular conformation and intermolecular interaction. The latter depends on the size of the orbital and number density. High-energy X-ray diffraction measurements and reverse Monte Carlo (RMC) structural modelling were performed for liquid S
2
Cl
2
in addition to the previous structural analysis for liquid Se
2
Br
2
. By comparing the structures of the RMC model and hard-sphere Monte Carlo (HSMC) model, the effect of refinement on the experimental structure factor can be analysed. In this paper, nearest-neighbour intermolecular pairs are classified in terms of enantiomer pairs such as like-pair (L-L and D-D) and unlike-pair (L-D). As a result, the effect of a strong intermolecular attractive interaction is detected in Se
2
Br
2
as increasing the number of like-pairs with geometrical advantages from HSMC to RMC, whereas that of an intermolecular repulsive interaction is observed in S
2
Cl
2
as elongation of the averaged intermolecular S-S distance from HSMC to RMC. These results are consistent with the results of the ab initio molecular dynamics simulation for Se
2
Cl
2
and S
2
Cl
2
.
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