arXiv subjects

Carlos Cárdenas

Publications and source records attributed to Carlos Cárdenas.

4 recordsLinked to original sources

arXiv2026

Ultrafast cation-dication dynamics in ammonia borane: H-migration to roaming H2 and reduced H3+ formation under strong-field ionization

We report a femtosecond time-resolved strong-field study of ammonia borane (AB, BH3NH3) following both single and double ionization, revealing ultrafast fragmentation dynamics and hydrogen release. Mass spectrometry, combined with fragment correlation analysis and ab initio molecular dynamics simulations, is used to identify the molecular origin of the neutral and ionic products. Singly ionized AB produces neutral H and H2, while doubly ionized AB produces neutral H and H2 along with H+, H2+, and H3+, all within 1 ps. Electronic-structure calculations show that H, H+, H2, H2+, and H3+ originate predominantly from hydrogen atoms bound to the boron center and that their formation proceeds through hydrogen migration and, in some channels, neutral H2 roaming. The calculations further indicate that the dication meets the structural and energetic requirements for neutral H2 release, a prerequisite for forming astrochemically relevant H3+. However, the large adiabatic relaxation energy causes most roaming H2 to dissociate before proton abstraction, suppressing H3+ formation. These results provide new insight into dissociative ionization pathways in hydrogen-rich molecules, extend mechanistic principles developed for halogenated alkanes to ammonia borane, and suggest implications for hydrogen-release chemistry in ammonia-borane-based storage materials.

physics.chem-ph↗

arXiv2023

Floquet Engineering of a Diatomic Molecule Through a Bichromatic Radiation Field

We report on a theoretical study of a Cs$_2$ molecule illuminated by two lasers and show how it can result in novel quantum dynamics. We reveal that these interactions facilitate the bypass of the non-crossing rule, forming Light-Induced Conical Intersections and modifiable avoided crossings. Our findings show how laser field orientation and strength, along with initial phase differences, can control molecular state transitions, especially on the micromotion scale. We also discuss extensively how the interaction of radiation with matter gives rise to the emergence of potential energy surfaces of hybrids of radiation and molecular states. This research advances a technique for manipulating photoassociation processes in Cs$_2$ molecules, offering potential new avenues in quantum control.

physics.chem-ph↗

arXiv2023

Carbon-based single photon emitters in hexagonal boron nitride with triplet ground state

Most single photon emitters in hexagonal boron nitride has been identified as carbon-based defects. These defects, when forming a donor-acceptor pair have spin $S\leq \frac{1}{2}$. By means of density functional calculations, we show that two non-adjacent carbon substitutional defects of the same type (i.e. C$_\mathrm{B}$-C$_\mathrm{B}$, and C$_\mathrm{N}$-C$_\mathrm{N}$), can have a triplet ground state. In particular, one of such defects has a zero phonon line energy of 2.5 eV, and its triplet state is nearly 0.5 eV more stable than its singlet.

cond-mat.mtrl-sci↗

arXiv2023

Formation of $\text{H}_{2}$ on polycyclic aromatic hydrocarbons under conditions of the ISM: an ab initio molecular dynamics study

Understanding how the $\mathrm{H}_2$ molecule is formed under the chemical conditions of the interstellar media (ISM) is critical to the whole chemistry of it. Formation of $\mathrm{H}_2$ in the ISM requires a third body acting as a reservoir of energy. Polycyclic aromatic hydrocarbons (PAH's) are excellent candidates to play that role. In this work we simulated the collisions of hydrogen atoms with coronene to form $\mathrm{H}_2$ via the Eley-Rideal mechanism. To do so, we used Born-Oppenheimer (ab initio) Molecular Dynamics simulations. Our results show that that adsorption of H atoms and subsequent release of $\mathrm{H}_2$ readily happen on coronene for H atoms with kinetic energy as large as 1 eV. Special attention is paid to dissipation and partition of the energy released in the reactions. The capacity of coronene to dissipate collision and reaction energies depends varies with the reaction site. Inner sites dissipate energy easier and faster than edge sites, thus evidencing an interplay between the potential energy surface around the reaction center and its ability to cool the projectile. As for the the recombination of H atoms and the subsequent formation of $\mathrm{H}_{2}$, it is observed that $\sim 15\%$ of the energy is dissipated by the coronene molecule as vibrational energy and the remaining energy is carried by $\mathrm{H}_{2}$. The $\mathrm{H}_{2}$ molecules desorb from coronene with an excited vibrational state ($\upsilon \geq 3$), a large amount of translational kinetic energy ($\geq$ 0.4 eV) and with a small activation of the rotational degree of freedom.

astro-ph.GA↗