RESUMEN
One-electron properties for molecules such as electron density, electrostatic potential (ESP), and electron momentum density (EMD) are experimentally tractable quantities, useful in understanding chemical characteristics. In this work, effects of a uniform homogeneous external electric field on some characteristic one-electron properties of simple molecules are analyzed. EMDs and ESPs were used to understand the response of water, hydrogen fluoride, carbon monoxide, chloroacetylene, and ammonia in an electric field. Remarkably, the EMD maxima for these molecules get rotated as the electric field strength is varied. A greater order of change in EMD than in ESP with increasing electric field strength brings out the sensitivity of the EMDs, especially for the valence electronic region, which in the momentum space is mapped onto the vicinity of its origin. The eigenvectors of the EMD Hessian maxima at the momentum-space origin are seen to rotate as a function of increasing field strength, with the extra angular momentum imparted by the field manifesting itself as reconfiguration of the EMD distribution. In the presence of the field, valence states may couple with higher electronic states, leading to a mixing of the states resulting in avoided crossings as a function of the field strength. The avoided crossings legitimately estimate maximal field strength limits for the calculation, prior to ionization.
RESUMEN
The dynamics of two electrons in a three-dimensional symmetric double-well quantum system is controlled using a high frequency oscillating electric field, achieving pairing of electrons and barrier-top localization. The field parameters of oscillating electric field intensity and frequency which are required to induce such an effect of barrier-top stabilization are easily estimated using time-independent Kramers-Henneberger electronic structure Full Configuration Interaction (FCI) calculations in an oscillating frame of reference with a Gaussian basis set. In the presence of the laser, the energy of the two-electron system in the symmetric double-well is found to be minimized when the barrier-top dynamic stabilization happens. Furthermore, the barrier-stabilized state finds importance in achieving a temporal control over electronic ionization. From approximate time-dependent calculations in the laboratory frame, the signatures of the barrier stabilized state are realized and it is observed that the paired-up state remains stable as long as the continuous wave region of the laser pulse is on. Ionization happens as soon as the laser pulse is switched off, because of the increased electronic repulsion in the paired up barrier-top state, thus giving a temporal control over laser-induced ionization.
RESUMEN
The photoexcitation of weakly bound complexes can lead to several decay pathways, depending on the nature of the potential energy surfaces. Upon excitation of a chromophore in a weakly bound complex, ionization of its neighbor upon energy transfer can occur due to a unique relaxation process known as intermolecular Coulombic decay (ICD), a phenomenon of renewed focus owing to its relevance in biological systems. Herein, we report the evidence for outer-valence ICD induced by multiphoton excitation by near-ultraviolet radiation of 4.4 eV photons, hitherto unknown in molecular systems. In the binary complexes of 2,6-difluorophenylacetylene with aliphatic amines, a resonant two-photon excitation localized on the 2,6-difluorophenylacetylene chromophore results in the formation of an amine cation following an outer-valence ICD process. The unique trends in experimentally observed translational energy distribution profiles of the amine cations following hydrogen bond dissociation, analyzed with the help of electronic structure and ab initio molecular dynamics calculations, revealed the presence of a delicate interplay of roaming dynamics, methyl-rotor dynamics, and binding energy.
RESUMEN
Point groups of molecules in a laser, within the Kramers-Henneberger (KH) oscillating frame for laser-dressed states, is given in this work. In a Fourier series of the time-dependent potential, the zeroth-order time-average yields the point group of the laser-dressed molecule. Various laser polarizations and relative molecular orientation induce a new point group or retain the original point group. The dynamical Fourier components (KH potentials) classify as irreducibles of this new laser-dressed point group. Recurrence of unique irreducibles in the Fourier expansion dictates the dynamical symmetry of the Floquet Hamiltonian. Hence, selection rules for harmonic generation spectra are Nk ± 1 in harmonic order, where N is the number of unique irreducibles and k∈N.
RESUMEN
The directionality of the chalcogen bond (Ch-bond) formed by S and its interplay with other weak interactions have important chemical and biological implications. Here, dimers made of CH3-S-X and O/N containing nucleophiles are studied and found to be stabilized by coexisting S···O/N and C-H···O/N interactions. Based on experimentally accessible electron density and molecular electrostatic potentials (MESPs), we showed that reciprocity between S···O/N and C-H···O/N interactions in the stability of cumulative molecular interaction (ΔE) was dependent on the strength of the σ-hole on S (Vs,max). Direct correlation between ΔE of dimers with Vs,max of S supports the electrostatic nature of the Ch-bond. Such interplay of the Ch-bond is necessary for its directionality in complex nucleophiles (carbonyl groups) with multiple electron-rich centers, which is explained using MESP. A correlation between the MESP minima in the π-region and the strength of the S-π interaction explains the directional selectivity of the Ch-bond.