Isotope-selective photodissociation is a promising route to laser-based separation, yet its efficiency remains constrained by fixed molecular cross sections. Here, we introduce an active optical-switching strategy that utilizes a nonresonant ultraviolet control pulse to generate and tailor isotopologue-specific Fano resonances. By coupling high-lying vibrational levels of the electronic ground state to a dissociative continuum, this pulse dynamically modulates photodissociation cross sections without direct electronic excitation. Using full quantum wave packet simulations of HF and DF isotopologues, we demonstrate that the photofragment yield ratio can be reversibly switched by orders of magnitude through tuning of the probe frequency across a light-induced resonance. This approach enables selective suppression or enhancement of dissociation for a target isotopologue with high spectral precision. Our work establishes a versatile and efficient mechanism for isotope-selective photochemistry and opens a pathway toward coherent optical control of molecular photodissociation.

Interference between scattering channels is observed in resonant inelastic x-ray scattering (RIXS) at the Ne K threshold. Final states with 2p-1np) as the main configuration are populated via 1s-1n'p) resonances, where large-amplitude one-electron (n' = n) channels interfere with small-amplitude two-electron (n' not equal n) channels. The interference is manifested in an asymmetric line profile where the two-electron resonance occurs in the tail region of the one-electron resonance. In RIXS, this slowly varying tail plays the role of the continuum for the Fano effect. The asymmetric profile is well modeled by means of a single asymmetry parameter, determined by the amplitudes of the scattering channels and the energy separation between the resonances.

We consider resonances induced by symmetry protected bound states in the continuum in dielectric gratings with in-plane mirror symmetry. It is shown that the shape of the resonance in transmittance is controlled by two parameters in a generic formula which can be derived in the framework of the coupled mode theory. It is numerically demonstrated that the formula encompasses various line-shapes including asymmetric Fano, Lorentzian, and anti-Lorentzian resonances. It is confirmed that the transmittance zeros are always present even in the absence up-down symmetry. At the same time reflectance zeros are not generally present in the single mode approximation. It is found that the line-shapes of Fano resonances can be predicted to a good accuracy by the random forest machine learning method which outperforms the standard least square methods approximation in error by an order of magnitude in error with the training dataset size.

Ultraviolet (UV) photodissociation provides valuable insights into fragmentation patterns and photochemical reactions. However, the limited overlap between vibrational bound states and continuum states hinders efficient quantum excitation. We address this challenge by embedding the ground bound potential into the dissociative continuum using a frequency-selected UV pulse. This pulse creates vibrational resonances by coupling the dissociative continuum with unpopulated vibrationally excited levels of the ground state, without initiating photoexcitation itself. Our findings demonstrate that the photodissociation spectra can be significantly manipulated by tuning the embedding pulse frequency to tailor the asymmetric profiles of the vibrational resonances. This is illustrated in our simulations of kinetic energy release spectra for both diatomic and polyatomic molecules. These proof-of-principle examples offer opportunities for manipulating the yield of photofragmentation and the pathways of photochemical reactions in various molecular systems.

The dynamics of chemical reactions in solution are of paramount importance in fields ranging from biology to materials science. Because the hydrogen-bond network and proton dynamics govern the behavior of aqueous solutions, they have been the subject of numerous studies over the years. Here, we report the observation of a previously unknown associative state in the hydroxide ion that forms when a proton from a neighboring water molecule approaches the hydroxide ion, utilizing resonant inelastic soft X-ray scattering (RIXS) and quantum dynamical simulations. State-of-the-art theoretical analysis reveals state mixing in the electronically excited states between aqueous hydroxide ions and the solvent. Our results give new insights into chemical bonding and excited-state dynamics in the aqueous environment. This investigation of associative states opens up new pathways for spectroscopic studies of chemical reaction dynamics and lays the foundation for directly accessing dynamic proton exchange in solution.

We theoretically consider orbital rotation of a spheroidal submicron particle in the field of two counter-propagating circularly polarized Gaussian beams. We derived equations connecting the parameters of the circular orbits centered on the beams axis to the optical force and torque. The equations show that, besides orbital rotation, the spheroidal particle simultaneously rotates around its equatorial axis. We found that two distinct dynamic regimes are possible. The orbital motion can be accompanied by a rapid proper rotation with angular velocity an order of magnitude larger than the angular velocity of the orbital rotation. Alternatively, the orbital and proper rotations can be synchronized. The direction of orbital rotation can either coincide with or be opposite to the direction of rotation of the electric vector. The findings are confirmed by direct numerical simulations. The results can be of use in development of nano-scale gyroscopes as well in shape-selective sorting of submicron particles. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Vibrationally resolved resonant Auger spectroscopy (RAS) on bound-continuum transitions enables highly sensitive probing of ultrafast dissociation in molecular core-excited states, where a distinct fragment band arises from Auger decay in dissociation fragments. Here, we theoretically investigate fragment band formation driven by ultrashort X-ray pulses. Unlike conventional molecular bands, fragment RAS peaks exhibit an insensitivity to strong X-ray Rabi oscillations. Numerical simulations on water molecules reveal that combining RAS with a fragment's kinetic energy release spectra enables clear observation of Rabi oscillation when the pulse broadening is smaller than the fragment's vibrational frequencies. This work establishes a framework for controlling ultrafast electron-nuclear dynamics in fragmentation by using X-ray pulses.

Photodissociation is one of the most important photoinduced chemical reactions. It occurs when the potential energy curve along a chemical bond is repulsive in an excited state. Typically, "ballistic" ultrafast dissociation leads to the broadening of absorption resonances and the smearing out of vibrational fine-structure. We report on the photodissociation of H2O in the (B) over tilde2(1)A(1) electronic state, characterized by a |3a(1)(-1)4a(1)(1)> configuration, which can be reached via resonant inelastic x-ray scattering or direct ultraviolet absorption. In both cases the spectra show narrow vibrational resonances, in spite of the dissociative character of the state. We find that "delayed" dissociation pathways, caused by reflection of the nuclear wave packet, are responsible for this effect. In spite of the analogous topology of the potential energy surfaces of the core- and valence-excited states, the reflection of the wave packet takes place only in the latter. The two-dimensional wave packet of the O-H stretching coordinates becomes trapped in a "cavity" near the Franck-Condon region, resulting from a mismatch between the OH vibrational frequency in the cavity and the one at the dissociation limit.

Different types of Young's double-slit experiments contain a significant amount of both particle and wave information running from full-particle to full-wave knowledge depending on the experimental conditions. We study the Young's double-slit interference in resonant Auger scattering from homonuclear diatomic molecules where opposite Doppler shifts for the dissociating atomic slits provide path information. Different quantitative formulation of Bohr's complementarity principle - path information vs interference - is applied to two types of resonant Auger scattering experiments, with fixed-in-space and randomly oriented molecules. Special attention is paid to the orientational dephasing in conventional Auger experiments with randomly oriented molecules. Our quantitative formulation of the complementarity is compared with the formulation made earlier by Greenberger and Yasin [D. M. Greenberger and A. Yasin, Phys. Lett. A 128, 391 (1988)0375-960110.1016/0375-9601(88)90114-4].

In this study, we integrate experimental observations and theoretical models to elucidate the complex phenomena observed in the resonant S K-edge KLL Auger scattering spectra of the SF6 molecule. A two-dimensional spectral map, constructed of incident photon energy and kinetic energy of the emitted Auger electron, is shown to be a versatile tool for understanding a character of the core-excited potential energy surface and change of the molecular geometry. Our findings reveal how the distinct dispersion behavior of multiple spectral lines enables mapping of ultrafast dynamics within the short-lived core-excited states. Our results confirm the presence of nuclear dynamics in the S1s-16a1g1 and S1s-16t1u1 core-excited states, while dynamics is absent in the S1s-17t1u1 state. Using a combination of ab initio analysis, simulations with Coulomb model potentials, and a simple analytical approximation, we qualitatively demonstrate how the varying characteristics of spectral dispersion - classified as Raman, non-Raman, and anti-Raman - mirror the relative gradients of the intermediate and final states in the resonant x-ray scattering process. This insight allows for the effective mapping of molecular potential energy curves, offering a prospective tool on the underlying mechanisms of resonant Auger scattering and its potential for probing molecular dynamics.