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Criegee intermediates, which are the result of ozonolysis of alkenes, play a key role in many chemical and physical processes in the Earth's atmosphere. Their reactions with various atmospheric compounds are responsible for formation of hydroxyl radicals, atomic oxygen and hydrogen, sulfuric and nitric acids, and other chemically active radicals and molecules. In this work we have considered collisional-induced chemical reactions between three simple Criegee intermediate molecules: CH2OO, CH3CHOO, and (CH3)2COO with methane, which is a well-known active greenhouse gas. Methane concentration rapidly growths last decades that causes serious concern to the global scientific community. It was established that reactions between methane and Criegee Intermediates can follow through two main routes. One of them occurs over exchange of oxygen and hydrogen atoms upon collision and leads to the formation of methanol. Another one pass through the formation of an intermediate complex with a deep energy minimum, and produces OH radicals and a variety of other products, among which are acetone, acetaldehyde, formaldehyde, propaldehyde, methanol, water molecules, and others. In this work, the both kinds of the reactions have been studied, and the relative reaction rates of both pathways have been compared. [ABSTRACT FROM AUTHOR]

Carbonyl oxides, or Criegee intermediates, play an important role in many physicochemical processes occurring in the Earth's atmosphere. Criegee intermediates are chemically active compounds that easily react with other atmospheric components, promoting the formation of OH and CH3 radicals, toxic compounds of nitrogen, and various acids. Traditionally, the literature considers reactions involving only those carbonyl oxides that are the most stable in the troposphere under the standard atmospheric conditions. In this study, it is shown that in the mesosphere and ionosphere, where the total concentration of molecules is low and the intensity of UV radiation and the number of free electrons are high, reactions involving electronically excited states of the Criegee intermediates CH3CHOO play a significant role. In this case, we should take into account the features of the decomposition of all isomers of the CH3CHOO molecule. [ABSTRACT FROM AUTHOR]

The increase in the concentration of methane in the atmosphere as a result of anthropogenic activity, melting of permafrost, and decomposition of gas hydrates on the seabed has attracted close attention of the scientific community in recent decades due to the potentially dangerous effect of methane on the ozone layer and the Earth's climate. According to various estimates, the greenhouse effect from methane is dozens of times stronger than the similar effect from carbon dioxide; therefore, the processes of methane transfer to the upper layers of the Earth's atmosphere, as well as its lifetime and interaction with other substances present in the stratosphere, mesosphere and ionosphere are of great scientific interest. In this study, we consider the chemical reactions occurring during collisions of methane molecules with methyl carbonyl oxide CH3CHOO in the upper atmosphere. It is shown that this process initiates the formation of the OH radical and starts a cascade of chemical reactions, the products of which are CH3, atomic hydrogen, acetone, acetaldehyde, propaldehyde, methyl alcohol, and water. These compounds are able to actively influence the composition of the atmosphere and its physicochemical properties. [ABSTRACT FROM AUTHOR]

The example of the lowest 1S resonance of the H– anion demonstrates that the resonance energy and its width calculated by way of finding the optimal point using the method of the complex absorbing potential has a systematic error, whose magnitude depends on the parameters of the absorbing potential and on the approximation used to solve the Schrödinger equation. It is shown that the accuracy of the calculation of resonance parameters can be improved if you replace finding the optimal point with averaging over the trajectory closure interval. [ABSTRACT FROM AUTHOR]

The ground and 10 lowest excited adiabatic electronic states of the Na2 dimer are calculated using the pseudopotential method. The use of the basis [7s6p5d4f] of atomic orbitals makes it possible to extend the range of available internuclear distances up to 1.7–50 Å. It is found that the theoretical values of the Te and De constants are in a good agreement with the experimental ones. Herein you will find the sample calculations of the radial non-adiabatic coupling matrix elements enable to transform the basis of the adiabatic states to quasidiabatic one. It is found also that the Le Roy modified radius scales down the left boundary of an asymptotic range for the electronic state with the (3s + 5p) dissociation limit and for the higher states. [ABSTRACT FROM AUTHOR]

Recently it has been theoretically predicted and experimentally confirmed that at altitudes of 80-110 km from the Earth's surface the signals of the global navigation satellite systems (GNSS) are delayed as a result of a multiple resonance scattering by the Rydberg complexes. The attenuation of GNSS signals occurs mainly in the lower atmosphere layers, where the greatest effect is achieved through interaction with charged aerosol layers. A thunderstorm conditions are of particular interest whereby the presence of strong electric fields and hydration of aerosols can lead to the detachment of OH radicals from water clusters. Since the spectrum of radiation and absorption of these radicals for rotational transitions is part of the microwave range, they are expected to make an additional resonance contribution to the delay of radio signals thus necessitating a detailed study of the electronic structure of the OH radical. This paper offers the ab initio calculations of the dipole moment function for the ground X2Π state of the OH molecule using the dipole length approach and the finite-field method. The comparison with the experiment shows that in extended model spaces the approximation of the dipole length leads to more accurate values of the dipole moment than the finite-field method. [ABSTRACT FROM AUTHOR]

Ab initio calculations of the adiabatic potential curves and matrix elements of radial nonadiabatic coupling of the N2 molecule for the states related to dissociation limits I-V were performed. The most important spectral characteristics of the adiabatic states agreed well with the available experimental and theoretical data. The diabatic states were constructed. The diabatic quantum defects and radial matrix elements of the configuration interaction of the dissociative and Rydberg configurations whose states converge to the ground state X2Σg+ and the first electronically excited state A2Πu of the N2+ ion were calculated. The possibility of using the results for calculating the cross sections and rate constants of dissociative recombination and associative ionization within the framework of the multichannel quantum defect theory was discussed. [ABSTRACT FROM AUTHOR]

A method was developed for calculating the vibronic potential energy surfaces (PESs) of atmospheric complexes consisting of orbitally degenerate Rydberg nitrogen and oxygen molecules and the molecules of a neutral medium in the ground electronic state. The degenerate states are formed as a result of L-mixing in the D and E layers of the atmosphere during the periods of increased solar activity. The complexes are populated in the nonequilibrium two-temperature plasma and are responsible for the incoherent additional background radiation in the decimeter (microwave) and terahertz (IR) bands at an altitude of 80-110 km from the Earth's surface. To describe the interaction ofa weakly bound electron with a singly charged molecular ion and a neutral molecule ofa gas medium, the formalism of the multichannel quantum defect (MCD) theory was used. Quantum-chemical calculations of the dependences of the scattering lengths, polarizabilities, and quadru-pole moments of the main atmospheric molecules N2 and 02 on the interatomic distance were performed. The specific features of the behavior of vibronic PESs of Rydberg complexes for large values of the principal quantum number (n⪢) were analyzed. The vibronic PESs of orbitally degenerate states were constructed. They are necessary for determining the positions and shape of the vibronic minima of the L-mixing cross sections of the N2 and 02 Rydberg molecules in the D and E layers of the Earth's atmosphere, where the delay times of satellite positioning signals should be minimum. The possibility of "quantum chaos" appearing in the Rydberg complexes at sufficiently large n values and angular momenta of the weakly bound electron was noted. [ABSTRACT FROM AUTHOR]

The origin of Λ-doubling effect (q factors) for the regularly perturbed NaK B [sup 1]∏ and D [sup 1]∏ states has been investigated by means of ab initio many-body multipartitioning perturbation theory calculation of the electronic L-uncoupling matrix elements between the examined [sup 1]∏ and five lowest [sup 1]∑[sup +] states for both [sup 23]Na[sup 39]K and [sup 23]Na[sup 41]K isotopomers. The hypothesis of pure precession was found to be valid for the B [sup 1]∏-A [sup 1]∑[sup +] and D [sup 1]∏-C [sup 1]∑[sup +] pairs of the interacted states, while the unique perturber approximation works properly for the D [sup 1]∏ state and completely breaks down for the B [sup 1]∏ state. The theoretical rovibronic q-factor values estimated for both states by means of the approximate sum rule agree well with their experimental counterparts and demonstrate high sensitivity to vibrational and rotational quantum numbers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]