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Molecular modification induced through the resonant attachment of a low energy electron (LEE) is a novel approach for molecular engineering. In this communication, we explore the possibility to use the LEE as a quantum tool for the in situ preparation of short lived molecules. Using ab initio quantum chemical methods, this possibility is best illustrated for the in situ preparation of the intrinsically short-lived carbon-carbon covalent dimer of CO from a glyoxal molecule. The chemical conversion of glyoxal to the covalent dimer of CO is initiated and driven by the resonant capture of a near 11 eV electron by the glyoxal molecule. The resulting two-particle one-hole (2p-1h) negative ion resonant state (NIRS) of the glyoxal molecule undergoes a barrierless radical dehydrogenation reaction and produces the covalent dimer of CO. The autoionization electron spectra from the 2p-1h NIRS at the dissociation limit of the dehydrogenation reaction provides access to the electronic states of the CO dimer. The overall process is an example of a catalytic electron reaction channel [ABSTRACT FROM AUTHOR]

By adding a negative imaginary potential of variable strength η to the Hamiltonian, the resonance state of a system can be found as complex energy stabilized points in the η-trajectories of the eigenvalues. One problem that arises in practical calculations is the appearance of nonphysical complex energy stabilized points. A new method for separating the physical from the nonphysical complex energy stabilized points is proposed. The method is best illustrated with strongly correlated two-electron systems. [ABSTRACT FROM AUTHOR]

In 1965, Davidson has shown that the textbook explanation for the Hund’s multiplicity rule in atoms, based on the Pauli principle, is wrong. The reason for the failure of the textbook proof, as has been given later by others and as appears today in modern textbooks, it is based on the need to introduce angular electronic correlation into the calculations. Here, we investigate an applicability of this argumentation for helium and for the case of two-electron spherically symmetric rectangular quantum dots (QDs). We show that, for helium and also for the QD, the differences between the singlet and triplet excited states can be explored by calculations within the framework of the mean-field approximation, and, surprisingly, without the need of introducing the angular electronic correlation. Moreover, our calculations have shown that the triplet state of the QD is lower in energy than the corresponding singlet state due to lower electronic repulsion contribution, exactly as being assumed in the oldest explanation of the Hund’s rule based on the Pauli principle. [ABSTRACT FROM AUTHOR]

The reflection-free complex absorbing potential (RF-CAP) method has been already applied to the study of the autoionization resonance of helium [Sajeev et al., Chem. Phys. 329, 307 (2006)]. The present work introduces a systematic way for implementing RF-CAP for the electronic structure calculations using Gaussian basis sets for molecules. As a test case study we applied the RF-CAP method to the lowest 1Σg+ and 1Σu+ Feshbach-type autoionization resonances of hydrogen molecule. Since thin RF-CAP absorbs fast electrons much better than the slow ones, a weak dc field has been added to the RF-CAP in the peripheral region of the molecule. [ABSTRACT FROM AUTHOR]

We have formulated and applied an analytic continuation method for the recently formulated correlated independent particle potential [A. Beste and R. J. Bartlett J. Chem. Phys. 120, 8395 (2004)] derived from Fock space multireference coupled cluster theory. The technique developed is an advanced ab initio tool for calculating the properties of resonances in the low-energy electron-molecule collision problem. The proposed method quantitatively describes elastic electron-molecule scattering below the first electronically inelastic threshold. A complex absorbing potential is utilized to define the analytic continuation for the potential. A separate treatment of electron correlation and relaxation effects for the projectile-target system and the analytic continuation using the complex absorbing potential is possible, when an approximated form of the correlated complex independent particle potential is used. The method, which is referred to as complex absorbing potential-based correlated independent particle (CAP-CIP), is tested by application to the well-known 2Πg shape resonance of e-N2 and the 2B2g shape resonance of e-C2H4 (ethylene) with highly satisfactory results. [ABSTRACT FROM AUTHOR]

The technique of Fock space multireference coupled-cluster (FSMRCC) is applied for the first time to the correlated calculation of the energy and width of a shape resonance in an electron-molecule collision. The procedure is based upon combining a complex absorbing potential with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigenvalue problem. The potential-energy curve of the 2Πg state of N2- is calculated using the FSMRCC and multireference configuration-interaction (MRCI) level of theories. Comparison with the single-determinant Hartree–Fock theory indicates that correlation effects are important in determining the behavior of the resonance state. [ABSTRACT FROM AUTHOR]

The Fock space multireference coupled cluster based on an underlying bivariational self-consistent field is applied to the problem of computing complex energy associated with Auger and shape resonances in e-atom scattering. It is concluded that the Fock space multireference coupled cluster based on a bivariational self-consistent field provides a useful and practical approach to calculation of resonance parameters. Numerical results are presented for the [sup 2]P shape resonance of Mg and Auger 1 s-1 hole of Be. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Static polarizability and first- and second-order hyperpolarizability tensors are computed at the correlated level for a series of para-nitroaniline derivatives. The importance of including electron correlation effects in the determination of equilibrium structure and the molecular properties is investigated.

State-specific reaction dynamics induced through the resonant attachment of a low energy electron (LEE) offers hitherto unavailable opportunities for the chemical synthesis of theoretically possible chemical structures. Using ab initio quantum chemical methods, this possibility is illustrated for the cycloaddition reaction of dinitrogen molecules to produce the anion of tetrazete , which is an all-nitrogen cyclic molecule. This LEE induced cycloaddition reaction, which is an associative electron attachment reaction, is initiated by the resonant attachment of a near 12 eV LEE to the dimer of non-interacting molecular dinitrogens, (N). The resulting 2p1h state of the (N) undergoes a barrierless cycloaddition reaction and produce N. In this reaction, the kinetic energy of the LEE is stored in the geometrical metastable structure of and make this process a potential method for storing energy. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of 4-bromo-2,3,5,6-tetrafluoropyridine (BTFP) have been studied in a supersonic molecular beam around 234 nm, which prepares the molecule in its ππ* state. The dynamics of the C Br bond dissociation have been investigated using resonance-enhanced multiphoton ionization coupled with time-of-flight mass spectrometer (REMPI-TOFMS) by detecting the nascent spin orbit states of the primary bromine atoms, namely, Br ( 2 P 3/2 ) and Br*( 2 P 1/2 ). State specific polarization dependent TOF profiles were obtained, from which the translational energy distributions and recoil anisotropy parameters, β i , were extracted using forward convolution method. A strong polarization dependence of TOF profiles suggests anisotropic distributions of the Br and Br* fragments. Two components, namely, the fast and the slow, are observed in the translational energy distribution of Br and Br* atoms, formed from different potential energy surfaces. The average translational energies released into the Br and Br* channels for the fast component are 17.3 ± 2.0 and 11.1 ± 2.0 kcal/mol, respectively. Similarly, for the slow component, the average translational energies imparted into the Br and Br* channels are 2.6 ± 1.0 and 1.5 ± 1.0 kcal/mol, respectively. The relative quantum yields of Br and Br* are 0.87 ± 0.15 and 0.13 ± 0.06. The anisotropy parameters for Br and Br* are characterized by a similar value of 0.60 ± 0.05. The energy partitioning into the translational modes is interpreted with the help of various models. The experimental studies revealing the nature of translational energies distribution for Br and Br* and its average value along with the theoretical calculations employing Time-Dependent Density Functional Theory (TD-DFT) and Multi Configuration Quasi Degenerate second order Perturbation Theory (MCQDPT2) suggest that the initially prepared ππ* state crosses over to a nearby σ* repulsive state along the C Br bond, mainly, πσ* state from where the dissociation takes place. The results also indicate the process of fast internal conversion to ground state from the initially prepared ππ* state, which eventually forms slow Br atoms after C-Br bond dissociation process on the ground state. During the course of experiments, the absorption spectrum was also obtained with its absolute absorption cross section. Non-adiabatic curve crossing plays an important role in the C Br bond dissociation of BTFP. [ABSTRACT FROM AUTHOR]

Ab initio quantum chemical studies show that a very weak molecular complexation of CO2 with a dipolar molecule is able to suppress the autoionization of the electron from its transient negative ion states. Since the autoionization is suppressed, the transient negative ion can efficiently relax its geometry to form the reductively activated CO2 moiety. Unlike the reductively activated isolated CO2 molecules, which are deactivated immediately due to their thermodynamic metastability, the reductively activated CO2 moieties of the weak molecular complexes are infinitely long-lived and, hence, permanently reactive. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formulation of an improved L 2-stabilization method for electronic resonances. [•] Formulation of a Hermitian based method for electronic resonances. [•] A formulation that helps to utilize all the existing ab initio codes for computing resonances-induced chemical reactions. [ABSTRACT FROM AUTHOR]

The article focuses on a study, which analyzes the presence and chemical evolution of nitrogen-bearing polycyclic aromatic hydrocarbons (PANHs) in space. It shows that light can efficiently trigger the molecular mass growth of PANHs, particularly through the association of ultraviolet-photoexcited quinoline monomers, leading to the formation of heavier cations. This mechanism reveals a pathway for PANHs' massive growth in space.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in space and govern the interstellar chemistry. The two isomers of cyanonaphthalene (1-CNN and 2-CNN) were the first PAHs to be recently identified in the Taurus Molecular Cloud (TMC-1). Their large abundance is attributed to high photostability with nearly no photofragmentation at photon energies above the ionization potential. Here, we show that at ambient light and at densities akin to dense molecular clouds and the upper atmosphere of planets and moons, 1-CNN could undergo extensive fragmentation through a new mechanism leading to daughter cations. On UV photoexcitation, at a photon energy way below the ionization threshold, 1-CNN monomers form photoexcited dimer units. Intermolecular Coulombic decay between the two photoexcited units of the dimer leads to ionization, and the subsequent molecular rearrangements form new daughter cations. These daughter cations could react further, contributing to rich bottom-up astrochemistry, and could play a pivotal role in developmental astrobiology. Photofragmentation in atmospheric and astrophysical environments is hitherto known to be unimolecular, while the present results point a pathway involving bimolecular photofragmentation., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Low energy electrons can initiate and control chemical reactions through resonant attachment forming an electron-molecule compound state. Recently, it has been theoretically shown that free electrons can also act as catalysts in chemical reactions. We investigate this novel concept for the case of conversion of formic acid into CO 2 . Resonant production of CO 2 from cold formic acid films by low energy electron impact is observed using Fourier transform infrared spectroscopy. The resonant peak observed at 6 eV is identified as the catalytic electron channel. The experimental results are augmented with the ab initio quantum chemical calculations.

The dc field Stark effect is studied theoretically for atoms in high intensity laser fields. We prove that the first-order perturbation corrections for the energy and photoionization rate vanish when the dc field strength serves as a perturbational strength parameter. Our calculations show that by applying a dc field in the same direction as the polarization direction of the ac field, the photoinduced ionization rate is almost entirely suppressed. This suppression is attributed to changes in the phase shift of the continuum atomic wave functions which can be controlled by the dc field.

The technique of Fock space multireference coupled-cluster (FSMRCC) is applied for the first time to the correlated calculation of the energy and width of a shape resonance in an electron-molecule collision. The procedure is based upon combining a complex absorbing potential with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigenvalue problem. The potential-energy curve of the (2)Pi(g) state of N2- is calculated using the FSMRCC and multireference configuration-interaction (MRCI) level of theories. Comparison with the single-determinant Hartree-Fock theory indicates that correlation effects are important in determining the behavior of the resonance state.