arXiv subjects

Yijue Ding

Publications and source records attributed to Yijue Ding.

9 recordsLinked to original sources

arXiv2025

Ground and low-lying excited state potential energy surfaces of diiodomethane in four dimensions

We report a set of adiabatic potential energy surfaces (PESs) for diiodomethane, including the ground electronic state and all excited states accessible via single-photon absorption near 260 nm. Although constrained to four dimensions, these PESs capture the essential photochemical processes following photoexcitation--namely, bond breaking and rearrangement among the methyl radical and the two iodine atoms. Constructed using an accurate and efficient spline interpolation algorithm, the PESs reproduce local features with high fidelity and exhibit overall smooth first-order derivatives, making them suitable for molecular dynamics simulations. We identify key stationary points on the ground-state PES and on three excited-state PESs, and map reaction pathways leading to $\text{CH}_2\text{I}+\text{I}$ dissociation via the intermediate formation of a $\text{CH}_2\text{I-I}$ isomer. These PESs provide a valuable resource for molecular dynamics studies, enabling detailed exploration of photochemistry in diiodomethane.

physics.chem-ph↗

arXiv2025

Modeling the coincident three-ion momentum imaging of diiodomethane photodissociation on reduced-dimensional potential energy surfaces

We present an efficient theoretical model to simulate observables in the time-resolved coincident three-ion Coulomb explosion experiment of diiodomethane. The model employs two degrees of freedom to describe the C-I bond breaking and the $\text{CH}_2\text{I}$ rotation during photodissociation, and three degrees of freedom to describe the coincident $\text{CH}_2^{+} + \text{I}^{2+} + \text{I}^{2+}$ fragmentation during the subsequent Coulomb explosion. By solving the equations of motion, the photodissociation pathways are obtained on two-dimensional potential energy surfaces of the valence excited states of the neutral molecule, and the asymptotic momenta of the three ionic fragments are determined on the three-dimensional ground-state potential energy surface of the fivefold-charged cation. The photodissociation pathways are consistent with previous \textit{ab initio} molecular dynamics simulations and indicate a $\text{CH}_2\text{I}$ rotational period of approximately 340 fs. The theoretical time-resolved kinetic energy release and the correlation between the kinetic energy release and the angle between the two $\text{I}^{2+}$ momenta show good agreement with experimental signals in part, reflecting and confirming the static $\text{CH}_2\text{I}_2$ state and the $\text{CH}_2\text{I} + \text{I}$ dissociation channels.

physics.chem-ph↗

arXiv2025

Imaging transient molecular configurations in UV-excited diiodomethane

Femtosecond structural dynamics of diiodomethane ($\mathrm{CH_2I_2}$) triggered by ultraviolet (UV) photoabsorption at 290 nm and 330 nm are studied using time-resolved coincident Coulomb explosion imaging driven by a near-infrared probe pulse. We map the dominant single-photon process, the cleavage of the carbon-iodine bond producing rotationally excited $\mathrm{CH_2I}$ radical, identify the contributions of the three-body ($\mathrm{CH_2} + \mathrm{I} + \mathrm{I}$) dissociation and molecular iodine formation channels, which are primarily driven by the absorption of more than one UV photon, and demonstrate the existence of a weak reaction pathway involving the formation of short-lived transient species resembling iso-$\mathrm{CH_2I{-}I}$ geometries with a slightly shorter I-I separation compared to the ground-state $\mathrm{CH_2I_2}$. These transient molecular configurations, which can be separated from the other channels by applying a set of conditions on the correlated momenta of three ionic fragments, are formed within approximately 100 fs after the initial photoexcitation and decay within the next 100 fs.

physics.chem-ph↗

arXiv2025

Ultrafast photodissociation dynamics of dichloromethane on three-dimensional potential energy surfaces and its Coulomb explosion signature

We present efficient and reliable molecular dynamics simulations of the photodissociation of dichloromethane followed by Coulomb explosion. These simulations are performed by calculating trajectories on accurate potential energy surfaces of the low-lying excited states of the neutral dichloromethane molecule. The subsequent time-resolved Coulomb explosions are simulated on the triply charged ionic state, assuming Coulomb interactions between ionic fragments. Both the neutral state trajectories and the simulated Coulomb explosion observables indicate that intra-molecular photoisomerization of dichloromethane is unlikely to occur. Estimating the kinetic energy release using \textit{ab initio} ionic potential reveals a discrepancy of approximately 5-8 eV compared to our simulated values using Coulomb potential. The molecular structural changes during photodissociation are clearly mapped to the ionic-fragment coincidence signals, demonstrating the Coulomb explosion imaging technique as a powerful tool to probe the time-resolved reaction dynamics.

physics.chem-ph↗

arXiv2025

Modeling the time-resolved Coulomb explosion imaging of halomethane photodissociation with \textit{ab initio} potential energy curves

We present an effective theoretical model to simulate observables in time-resolved two-fragment Coulomb explosion experiments. The model employs the potential energy curves of the neutral molecule and the doubly charged cation along a predefined reaction coordinate to simulate the photodissociation process followed by Coulomb explosion. We compare our theoretical predictions with pump-probe experiments on iodomethane and bromoiodomethane. Our theory successfully predicts the two reaction channels in iodomethane photodissociation that lead to $\text{I}(^2\text{P}_{3/2})$ and $\text{I}^*(^2\text{P}_{1/2})$ products, showing excellent agreement with experimental delay-dependent kinetic energy release signals at large pump-probe delays. The theoretical kinetic energy release at small delays depends significantly on the choice of ionic states. By accounting for internal rotation, the kinetic energies of individual fragments in bromoiodomethane align well with experimental results. Furthermore, our theory confirms that two-fragment Coulomb explosion imaging cannot resolve different spin channels in bromoiodomethane photodissociation.

physics.chem-ph↗

arXiv2024

Surface hopping molecular dynamics simulation of ultrafast methyl iodide photodissociation mapped by Coulomb explosion imaging

We present a highly efficient method to directly simulate the photodissociation followed by Coulomb explosion of methyl iodide. In order to achieve statistical reliability, more than 40,000 trajectories are calculated on accurate potential energy surfaces of both the neutral molecule and the doubly charged cation. Non-adiabatic effects during photodissociation are treated using a Landau-Zener surface hopping algorithm. The simulation is performed analogous to a recent pump-probe experiment using coincident ion momentum imaging [Ziaee \textit{et al., Phys. Chem. Chem. Phys.} 2023, \textbf{25}, 9999]. At large pump-probe delays, the simulated delay-dependent kinetic energy release signals show overall good agreement with the experiment, with two major dissociation channels leading to $\text{I}(^2\text{P}_{3/2})$ and $\text{I}^*(^2\text{P}_{1/2})$ products. At short pump-probe delays, the simulated kinetic energy release shows a clear bifurcation near 12 fs, owing to non-adiabatic transitions through a conical intersection. The developed method is particularly suitable and efficient in simulating processes that highly rely on statistics or for identifying rare reaction channels.

physics.chem-ph↗

arXiv2020

Spin-momentum entanglement in a Bose-Einstein condensate

Entanglement is at the core of quantum information processing and may prove essential for quantum speed-up. Inspired by both theoretical and experimental studies of spin-momentum coupling in systems of ultra-cold atoms, we investigate the entanglement between the spin and momentum degrees of freedom of an optically trapped BEC of $^{87}$Rb atoms. We consider entanglement that arises due to the coupling of these degrees of freedom induced by Raman and radio-frequency fields and examine its dependence on the coupling parameters by evaluating von Neumann entropy as well as concurrence as measures of the entanglement attained. Our calculations reveal that under proper experimental conditions significant spin-momentum entanglement can be obtained, with von Neumann entropy of 80% of the maximum attainable value. Our analysis sheds some light on the prospects of using BECs for quantum information applications.

quant-ph↗

arXiv2017

Renormalized contact interaction in degenerate unitary Bose gases

We renormalize the two-body contact interaction based on the exact solution of two interacting particles in a harmonic trap. This renormalization extends the validity of the contact interaction to large scattering lengths. We apply this renormalized interaction to a degenerate unitary Bose gas to study its stationary properties and elementary excitations using the mean-field theory and the hyperspherical method. Since the scattering length is no longer a relevant length scale at unitarity, universal properties are obtained that depend only on the average particle density. Our treatment shows that the universal relations for the total energy and for the two-body contact are $E/N=12.67\hbar^2\langle n^{2/3}\rangle/2m$ and $C_{2}/N=11.8\langle n^{1/3}\rangle$ respectively.

physics.atom-ph↗

arXiv2016

Effective Control of Cold Collisions with Radio Frequency Fields

We study $^{87}$Rb cold collisions in a static magnetic field and a single-color radio frequency (RF) field by employing the multi-channel quantum defect theory in combination with the Floquet method to solve the two-body time-dependent Schrödinger equation. Our results show that RF fields can modify the two-body scattering length by a large scale through Feshbach resonances both in low and high static magnetic field regimes. Such RF induced Feshbach resonances can be applied to quenching experiments or controlling interactions in spinor condensates. Here, we also show that analogous to photo-association, RF fields can also associate cold atoms into molecules at a useful rate.

physics.atom-ph↗