scholarly journals The smallest proton-bound dimer H 5 + : theoretical progress

2019 ◽  
Vol 377 (2154) ◽  
pp. 20180396 ◽  
Author(s):  
Rita Prosmiti ◽  
Álvaro Valdés
Keyword(s):  
Proton Transfer ◽  
Molecular Ions ◽  
Laboratory Observation ◽  
Vibrational Dynamics ◽  
Theoretical Approaches ◽  
Large Amplitude Motions ◽  
Spectral Simulations ◽  
Molecular Astrophysics ◽  
Structure Calculations ◽  
Full Quantum

The protonated hydrogen dimer, H 5 + , is the smallest system including proton transfer, and has been of long-standing interest since its first laboratory observation in 1962. H 5 + and its isotopologues are the intermediate complexes in deuterium fractionation reactions, and are of central importance in molecular astrophysics. The recently recorded infrared spectra of both H 5 + and D 5 + reveal a rich vibrational dynamics of the cations, which presents a challenge for standard theoretical approaches. Although H 5 + is a four-electron ion, which makes highly accurate electronic structure calculations tractable, the construction of ab initio -based potential energy and dipole moment surfaces has proved a hard task. In the same vein, the difficulties in treating the nuclear motion could also become cumbersome due to their high dimensionality, floppiness and/or symmetry. These systems are prototypical examples for studying large-amplitude motions, as they are highly delocalized, interconverting between equivalent minima through internal rotation and proton transfer motions requiring state-of-the-art treatments. Recent advances in the computational vibrational spectroscopy of the H 5 + cation and its isotopologues are reported from full quantum spectral simulations, providing important information in a rigorous manner, and open perspectives for further future investigations. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

scholarly journals Non-Covalent Forces in Naphthazarin—Cooperativity or Competition in the Light of Theoretical Approaches

2021 ◽  
Vol 22 (15) ◽  
pp. 8033
Author(s):  
Aneta Jezierska ◽  
Kacper Błaziak ◽  
Sebastian Klahm ◽  
Arne Lüchow ◽  
Jarosław J. Panek
Keyword(s):  
Monte Carlo ◽  
Perturbation Theory ◽  
Potential Energy ◽  
Proton Transfer ◽  
Ir Spectra ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Theoretical Approaches ◽  
Study Results ◽  
Intramolecular Hydrogen

Non-covalent interactions responsible for molecular features and self-assembly in Naphthazarin C polymorph were investigated on the basis of diverse theoretical approaches: Density Functional Theory (DFT), Diffusion Quantum Monte Carlo (DQMC), Symmetry-Adapted Perturbation Theory (SAPT) and Car-Parrinello Molecular Dynamics (CPMD). The proton reaction paths in the intramolecular hydrogen bridges were studied. Two potential energy minima were found indicating that the proton transfer phenomena occur in the electronic ground state. Diffusion Quantum Monte Carlo (DQMC) and other levels of theory including Coupled Cluster (CC) employment enabled an accurate inspection of Potential Energy Surface (PES) and revealed the energy barrier for the proton transfer. The structure and reactivity evolution associated with the proton transfer were investigated using Harmonic Oscillator Model of Aromaticity - HOMA index, Fukui functions and Atoms In Molecules (AIM) theory. The energy partitioning in the studied dimers was carried out based on Symmetry-Adapted Perturbation Theory (SAPT) indicating that dispersive forces are dominant in the structure stabilization. The CPMD simulations were performed at 60 K and 300 K in vacuo and in the crystalline phase. The temperature influence on the bridged protons dynamics was studied and showed that the proton transfer phenomena were not observed at 60 K, but the frequent events were noticed at 300 K in both studied phases. The spectroscopic signatures derived from the CPMD were computed using Fourier transformation of autocorrelation function of atomic velocity for the whole molecule and bridged protons. The computed gas-phase IR spectra showed two regions with OH absorption that covers frequencies from 2500 cm−1 to 2800 cm−1 at 60 K and from 2350 cm−1 to 3250 cm−1 at 300 K for both bridged protons. In comparison, the solid state computed IR spectra revealed the environmental influence on the vibrational features. For each of them absorption regions were found between 2700–3100 cm−1 and 2400–2850 cm−1 at 60 K and 2300–3300 cm−1 and 2300–3200 cm−1 at 300 K respectively. Therefore, the CPMD study results indicated that there is a cooperation of intramolecular hydrogen bonds in Naphthazarin molecule.

scholarly journals A simplistic computational procedure for tunneling splittings caused by proton transfer

2021 ◽  
Author(s):  
Denis S. Tikhonov
Keyword(s):  
Schrödinger Equation ◽  
Proton Transfer ◽  
Schrodinger Equation ◽  
Zero Point ◽  
Computational Procedure ◽  
Basis Set ◽  
Hartree Fock ◽  
Tunneling Splittings ◽  
Complete Basis Set ◽  
Large Amplitude Motions

AbstractIn this manuscript, we present an approach for computing tunneling splittings for large amplitude motions. The core of the approach is a solution of an effective one-dimensional Schrödinger equation with an effective mass and an effective potential energy surface composed of electronic and harmonic zero-point vibrational energies of small amplitude motions in the molecule. The method has been shown to work in cases of three model motions: nitrogen inversion in ammonia, single proton transfer in malonaldehyde, and double proton transfer in the formic acid dimer. In the current work, we also investigate the performance of different DFT and post-Hartree–Fock methods for prediction of the proton transfer tunneling splittings, quality of the effective Schrödinger equation parameters upon the isotopic substitution, and possibility of a complete basis set (CBS) extrapolation for the resulting tunneling splittings.

scholarly journals Modern Theoretical Approaches to Modeling the Excited-State Intramolecular Proton Transfer: An Overview

Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5140 ◽  
Author(s):  
Joanna Jankowska ◽  
Andrzej L. Sobolewski
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Quantum Dynamics ◽  
Intramolecular Proton Transfer ◽  
Experimental Investigations ◽  
Chemical Methods ◽  
Theoretical Approaches ◽  
Quantum Chemical Methods ◽  
Process Studies ◽  
Different Levels

The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.

scholarly journals High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium

Atoms ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 67 ◽  
Author(s):  
Robert Beuc ◽  
Mladen Movre ◽  
Goran Pichler
Keyword(s):  
High Temperature ◽  
Thermodynamic Equilibrium ◽  
Bound States ◽  
Local Thermodynamic Equilibrium ◽  
Classical Method ◽  
Rotational Quantum Number ◽  
Computer Time ◽  
Quantum Mechanical ◽  
Theoretical Approaches ◽  
Full Quantum

In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound–bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck–Condon principle and the stationary–phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li2, and Cs2 molecules in the high temperature range.

scholarly journals Large Amplitude Motions of Pyruvic Acid (CH3-CO-COOH)

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4269
Author(s):  
María Luisa Senent ◽  
Samira Dalbouha
Keyword(s):  
Pyruvic Acid ◽  
Energy Levels ◽  
Point Group ◽  
Spectroscopic Properties ◽  
Three Dimensions ◽  
Theoretical Approaches ◽  
Variational Calculations ◽  
Large Amplitude Motions ◽  
Highly Correlated ◽  
Methyl Torsion

Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the Cs point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406–986 cm−1 region and represent excitations of the ν24 (skeletal torsion) and the ν23 (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν23. The A1/E splitting of the ground vibrational state has been evaluated to be 0.024 cm−1 as it was expected given the high of the methyl torsional barrier (338 cm−1). A very good agreement with respect to previous experimental data concerning fundamental frequencies (νCAL − νEXP ~ 1 cm−1), and rotational parameters (B0CAL − B0EXP < 5 MHz), is obtained.

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