arXiv subjects

Jesús González-Vázquez

Publications and source records attributed to Jesús González-Vázquez.

6 recordsLinked to original sources

arXiv2026

Photoinduced enhancement of chemical shift sensitivity to local vibrations

The advent of novel free-electron laser sources enabling time-resolved x-ray photoelectron spectroscopy (tr-XPS) provides a unique opportunity to monitor local chemical environments in real time by measuring sub-eV shifts in core-electron binding energies. These shifts reflect the interplay between electronic excitation and nuclear motion, an interplay that remains largely unexplored. In our combined theoretical and experimental study of fluoropyridine (C$_5$H$_4$FN), we investigate this link by monitoring the evolving chemical environment at the N and F atomic sites as the photoexcited $S_1$ state relaxes to the ground state via a conical intersection. We find that the F site responds primarily to vibrational relaxation, showing minimal sensitivity to the electronic excited state. In contrast, excitation to $S_1$ induces a measurable energy shift at the N site and significantly enhances its sensitivity to local vibrations within the ring. This behavior arises from a photoinduced redistribution of charge, which also increases the Coulomb interaction between the 1s electron at the N atom and the atomic partial charge at an adjacent C atom. This insight opens new avenues for exploring ultrafast dynamics and conical intersection pathways in more complex systems, from photostable DNA bases to light-harvesting materials.

physics.chem-ph↗

arXiv2025

Unraveling real-time chemical shifts in the ultrafast regime

Traditional x-ray photoelectron spectroscopy (XPS) relies upon a direct mapping between the photoelectron binding energies and the local chemical environment, which is well-characterized by an electrostatic partial charges model for systems in equilibrium. However, the extension of this technique to out-of-equilibrium systems has been hampered by the lack of x-ray sources capable of accessing multiple atomic sites with high spectral and temporal resolution, as well as the lack of simple theoretical procedures to interpret the observed signals. In this work we employ multi-site XPS with a narrowband femtosecond x-ray probe to unravel different ultrafast dissociation processes of a polyatomic molecule, fluoromethane (CH$_{3}$F). We show that XPS can follow the cleavage of both the C-F and C-H bonds in real time, despite these channels lying close in binding energy. Additionally, we apply the partial charges model to describe these dynamics, and verify this extension with both advanced ab-initio calculations and experimental data. These results enable the application of this technique to out-of-equilibrium systems of higher complexity, by correlating real-time information from multiple atomic sites and interpreting the measurements through a viable theoretical modelling.

physics.chem-ph↗

arXiv2024

Non adiabatic dynamics of photoexcited cyclobutanone: predicting structural measurements from trajectory surface hopping with XMS-CASPT2 simulations

For years, theoretical calculations and scalable computer simulations have complemented ultrafast experiments as they offer the advantage to overcome experimental restrictions and have access to the whole dynamics. This synergy between theory and experiment promises to yield a deeper understanding of photochemical processes, offering valuable insights into the behavior of complex systems at the molecular level. However, the capacity of theoretical models to predict ultrafast experimental outcomes has remained largely unexplored. In this work, we aim to predict the electron diffraction signals of an upcoming ultrafast photochemical experiment using high-level electronic structure calculations and non adiabatic dynamics simulations. In particular, we perform trajectory surface hopping with XMSCASPT2 simulations for understanding mechanistic photodissociation of cyclobutanone upon excitation at 200 nm.

physics.chem-ph↗

arXiv2022

Nonadiabatic ab initio molecular dynamics including spin-orbit coupling and laser fields

Nonadiabatic ab initio molecular dynamics (MD) including spin-orbit coupling (SOC) and laser fields is investigated as a general tool for studies of excited-state processes. Up to now, SOCs are not included in standard ab initio MD packages. Therefore, transitions to triplet states cannot be treated in a straightforward way. Nevertheless, triplet states play an important role in a large variety of systems and can now be treated within the given framework. The laser interaction is treated on a non-perturbative level that allows nonlinear effects like strong Stark shifts to be considered. As MD allows for the handling of many atoms, the interplay between triplet and singlet states of large molecular systems will be accessible. In order to test the method, IBr is taken as a model system, where SOC plays a crucial role for the shape of the potential curves and thus the dynamics. Moreover, the influence of the nonresonant dynamic Stark effect is considered. The latter is capable of controlling reaction barriers by electric fields in timereversible conditions, and thus a control laser using this effect acts like a photonic catalyst. In the IBr molecule, the branching ratio at an avoided crossing, which arises from SOC, can be influenced.

physics.chem-ph↗

arXiv2019

Control defeseance by anti-alignment in the excited state

We predict anti-alignment dynamics in the excited state of H2+ or related homonuclear dimers in the presence of a strong field. This effect is a general indirect outcome of the strong transition dipole and large polarizabilities typically used to control or to induce alignment in the ground state. In the excited state, however, the polarizabilities have the opposite sign than in the ground state, generating a torque that aligns the molecule perpendicular to the field, deeming any laser-control strategy impossible.

physics.chem-ph↗

arXiv2017

Predissociation of methyl cyanoformate: The HCN and HNC channels

We present a combined experimental and theoretical investigation of the 193 nm photolysis of the cyano-ester, methyl cyanoformate (MCF). Specifically, nanosecond time-resolved infrared emission spectroscopy was used to monitor the ro-vibrationally excited photoproducts generated in the photolysis reaction. The signal-to-noise of all time-resolved spectra were enhanced using the recently developed algorithm, spectral reconstruction analysis, which allowed observation of previously obscured minor resonances, and revealed new dissociation channels producing HCN and HNC. Spectral fit analysis of the nascent HCN and electronically excited CN($A^2Π_1$) resonances yield a lower bound estimate for the HCN quantum yield of ca. 0.42$\pm$0.24%. Multi-configuration self-consistent field calculations were used to interrogate the ground and four lowest energy singlet excited states of MCF. At 193 nm, dissociation is predicted to occur predominantly on the repulsive S$_2$ state. Nevertheless, minor pathways leading to the production of highly excited ground state MCF are available via cascading internal conversion from nascent S$_2$ population. An automated transition-state search algorithm was employed to identify the corresponding ground state dissociation channels, and Rice-Ramsperger-Kassel-Marcus and Kinetic Monte Carlo kinetic simulations were used to calculate the associated branching ratios. The proposed mechanism was validated by direct comparison of the experimentally measured and quasi-classical trajectory deduced nascent internal energy distribution of HCN, which were found to be in near perfect agreement. The propensity for cyano containing hydrocarbons to act as photolytic sources for ro-vibrationally excited HCN and HNC, as well as their significance to astrophysical environments, are discussed.

physics.chem-ph↗