Predicting Kinetics of Spin-Forbidden Unimolecular Reactions with Nonadiabatic Transition State Theory

The central theme of this work is computational modeling of spin-forbidden kinetics of unimolecular reactions in the gas phase. We address in detail the nonadiabatic transition state theory (NA-TST), discuss its main advantages and shortcomings, and describe all critical steps to be taken to calculate the rate constants of spin-forbidden unimolecular reactions and the lifetimes of excited states decaying through intersystem crossing. We also discuss the recent implementation and use of the Zhu-Nakamura formulas coupled with NA-TST. These formulas provide complete set of solutions for the probability of transition between two electronic states for all coupling regimes and, in addition, they account for the curvature of the crossing potentials. We demonstrate that the 3B1→1A1 intersystem crossing rates in GeH2 predicted by NA-TST are in good agreement with the rates obtained with the nonadiabatic ab initio multiple spawning molecular dynamics. We also investigate the T1→S0 intersystem crossing in Cl2CS using single- and multireference electronic structure methods and compare the predicted microcanonical rate constants with previously reported theoretical and experimental values. We propose a zero-point energy correction scheme that can improve the intersystem crossing rate constants at the low energies. In the last part of this work, we study the fluorescence of a newly synthesized M2BiQ fluorophore, which is a promising candidate for chemical sensors and light-emitting devices. We show that fluorescence of this compound can be tuned to specific wavelengths throughout the visible spectrum by insertion of metal cations and by protonation. We show that coordination of M2BiQ to the metal cation is followed by stabilization of the excited emitting state with respect to the ground state. This stabilization results in reduction of the electronic gap and therefore in the large red shift observed for M2BiQ complexes

THEORETICAL FOUNDATIONS FOR RATE RAISING OF UNDERGROUND DRIVING BY HOLE BLASTING MANNERS AT PIT AND AT MINES

There the purposes are to develop the theoretical foundations to raise the rate of driving by the hole blasting manner, to predict the characteristics of machines, to organize the works at the face. The methods of mathematical simulation and of prediction of characteristics of face machines, of hole blasting for the major decrease of labour-intensiveness of driving have been developed. The developed methods were used at the enterprises and in the design institutes to substatiate the technical and organization approaches of high-rate evolution of driving, which were accepted for use, to create the outlook number of face machines. The manuals and the instructions to raise the rate of driving by the hole blasting manner are used at the pits and at the mines. 6 standardizing documents to raise the rate of driving and to improve the hole blasting have been developed and have been introduced. The application fields are the pits and the mines (the driving in the tough rocks)Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Dipole Moment Calculations Using Multiconfiguration Pair-Density Functional Theory and Hybrid Multiconfiguration Pair-Density Functional Theory

The dipole moment is the molecular property that most directly indicates molecular polarity. The accuracy of computed dipole moments depends strongly on the quality of the calculated electron density, and the breakdown of single-reference methods for strongly correlated systems can lead to poor predictions of the dipole moments in those cases. Here, we derive the analytical expression for obtaining the electric dipole moment by multiconfiguration pair density functional theory (MC-PDFT), and we assess the accuracy of MC-PDFT for predicting dipole moments at equilibrium and nonequilibrium geometries. We show that MC-PDFT dipole moment curves have reasonable behavior even for stretched geometries, and they significantly improve upon the CASSCF results by capturing more electron correlation. The analysis of a dataset consisting of 18 first-row transition metal diatomics and 6 main-group polyatomic molecules with multireference character suggests that MC-PDFT and its hybrid extension (HMC-PDFT) perform comparably to CASPT2 and MRCISD+Q methods and have a mean unsigned deviation of 0.2–0.3 D with respect to the best available dipole moment reference values. We explored the dependence of the predicted dipole moments upon the choice of the on-top density functional and active space, and we recommend the tPBE and hybrid tPBE0 on-top choices for the functionals combined with the moderate correlated participating orbital scheme for selecting the active space. With these choices, the mean unsigned deviations (in debyes) of the calculated equilibrium dipole moments from the best estimates are 0.77 for CASSCF, 0.29 for MC-PDFT, 0.24 for HMC-PDFT, 0.28 for CASPT2, and 0.25 for MRCISD+Q. These results are encouraging because the computational cost of MC-PDFT or HMC-PDFT is largely reduced compared to the CASPT2 and MRCISD+Q methods

Role of Triplet States in the Photodynamics of Aniline

The dynamics of excited heteroaromatic molecules is a key to understanding the photoprotective properties of many biologically relevant chromophores that dissipate their excitation energy nonreactively and thereby prevent the detrimental effects of ultraviolet radiation. Despite their structural variability, most heteroaromatic compounds share a common feature of a repulsive 1πσ* potential energy surface. This surface can lead to photoproducts, and it can also facilitate the population transfer back to the ground electronic state by means of a 1πσ*/S0 conical intersection. Here, we explore a hidden relaxation route involving the triplet electronic state of aniline, which has recently been discovered by means of time-selected photofragment translational spectroscopy [J. Chem. Phys. 2019, 151, 141101]. By using the recently available analytical gradients for multiconfiguration pair-density functional theory, it is now possible to locate the minimum energy crossing points between states of different spin and therefore compute the intersystem crossing rates with a multireference method, rather than with the less reliable single-reference methods. Using such calculations, we demonstrate that the population loss of aniline in the T1(3ππ*) state is dominated by C6H5NH2→C6H5NH⸱ + H⸱ dissociation, and we explain the long nonradiative lifetimes of the T1(3ππ*) state at the excitation wavelengths of 294‑264 nm

Ilimsk Ostrog: its Historical and Dendro-Chronological Aspects

This article focuses on dating the unique monument of wooden architecture from the time of the Russian colonization of Siberia - the Ilimsk stockaded town (the Saviour Tower of the Ilimsk stockaded town and the Ilimsk Kazan church). The monument is studied using dendrochronological analysis. This method is based on variable annual growth of tree-rings, and provides the most objective date with an accuracy of up to a year. The results of investigations confirm traditional dates of construction for the Saviour Tower of the Ilimsk stockaded town and the Ilimsk Kazan church.Статья посвящена теме датирования уникального памятника деревянного зодчества эпохи русской колонизации Сибири - Илимского острога (Спасская башня Илимского острога и Илимская церковь Казанской иконы Божией Матери). Для исследования использован дендрохронологический анализ, позволяющий на основе изменчивости прироста годичных колец деревьев получить наиболее объективные даты с точностью до года. Результаты исследования подтверждают традиционно принятые в исторической литературе даты сооружения Спасской башни Илимского острога и Илимской Казанской церкви

The age and origin of alkaline rocks of the Dakhunur pluton, South-Eastern Tuva

The research is aimed at proving the age, nature of parental magma sources, and geodynamic conditions, under which alkaline intrusives of the Tuva Mongolian terrain were introduced. That is relevant when reconstructing development of the Paleoasian Ocean and Paleozoic magmatism in folded frames of the Siberian Craton. The studied Dakhunur intrusion of ultrabasic foidolites and foyaites in the Sangilen Upland is an Early Carboniferous derivative of a Paleozoic alkaline magmatism of the South-Eastern Tuva. According to the precision isotopic Ar-Ar data obtained for the first time, its formation took place ~ 328 Ma. Geochemical features of alkaline rocks of pluton revealed by ICP-MS method indicate the intrusion occurred in a difficult geodynamic environment, where mantle plume interacted with accretionary complexes of active continental margin. Based on this fact, the duration and conditions of a tectonic regime of formation of one of the largest igneous provinces in the Central Asian folded belt are estimated

Nonadiabatic Transition State Theory: Application to Intersystem Crossings in the Active Sites of Metal-Sulfur Proteins

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Nonadiabatic transition state theory (NA-TST) is a powerful tool to investigate the nonradiative transitions between electronic states with different spin multiplicities. The statistical nature of NA-TST provides an elegant and computationally inexpensive way to calculate the rate constants for intersystem crossings, spin-forbidden reactions, and spin-crossovers in large complex systems. The relations between the microcanonical and canoni- cal versions of NA-TST and the traditional transition state theory are shown, followed by a review of the basic steps in a typical NA-TST rate constant calculation. These steps include evalua- tions of the transition probability and coupling between electronic states with different spin multiplicities, a search for the minimum energy crossing point (MECP), and computing the densities of states and partition functions for the reactant and MECP structures. The shortcomings of the spin-diabatic version of NA-TST related to ill-defined state coupling and state count- ing are highlighted. In three examples, we demonstrate the application of NA-TST to intersystem crossings in the active sites of metal-sulfur proteins focusing on [NiFe]-hydrogenase, rubre- doxin, and Fe2S2-ferredoxin. 2016 Wiley Periodicals, Inc