Annotation of the results obtained in 2020
As part of the low pressure LIBS experiments, a vacuum chamber was set up with a minimum pressure in the chamber of 1.6*10-3 Torr. The aberration was minimized for three optical path lengths and an expected plasma size of 1 cm. The measurements were carried out at pressures corresponding to the observation altitudes of the Beneshev meteoroid.In the evaporation of a pure iron, practically no molecular bands were observed, which indicates that the main source of FeO is the target material, and not the formation of molecules at the flame periphery, which was observed during the evaporation of pure iron in air [6]. Accordingly, a Fe304 target was used to study the time evolution of the the orange bands FeO system at low pressure. Since the ablation rate increases significantly with decreasing pressure, the target was continuously rotated and all measurements were carried out at the same amplification of the recorded signal. To evaluate the temperature, we used the Boltzmann graph plotted for atomic lines in the range of 510-524 nm, for which self-absorption according to the simulation data is negligible. The dimensions of the laser plasma increase significantly with decreasing pressure, reaching 2–3 cm in diameter at the minimal pressure, which is consistent with the literature data. For the emission spectra of plasma upon laser evaporation of the Fe304 target and a reduced pressure, a significant increase in the relative intensity of atomic lines (by more than an order of magnitude) was observed for all plasma evolution times. The intensity of the bands at pressures of 32 and 16 Torr is generally comparable to that observed at atmospheric pressure; however, with decreasing pressure, the relative intensity in the range 622–628 nm also decreases. This fact supports the hypothesis that the observed burst in intensity should be attributed to the contribution from higher iron oxides. Since the plasma emission rapidly decays at pressures of 0.6 and 0.16 Torr, the measurements were carried out with a delay of 1 μs. An interesting fact is that at small delays and low pressures, the peak at 622 nm increases slightly again, which may indicate the correctness of assumption that the source of the formation of molecules at low pressures is the target material. To establish the exact mechanism of FeO formation at different pressures, additional spatially resolved measurements are required either using probe methods (for example, fluorescence) or performing the Abel transformation to reconstruct the intensity distribution profile within the plume. An interesting feature of the evolution of a laser plume at low pressures is an increase in the electron temperature at late observation times. This effect can be associated either with thermalization of the kinetic energy of electrons, or with the excitation of meta-stable states of atmospheric gases with a gradual collision transfer of energy from them to iron atoms.In addition to the molecular bands of FeO, the bands of the orange system of CaO also significantly complicate the interpretation of the spectra of meteoroids in the range of 580-630 nm. Although fluorescence spectra with a resolved vibrational-rotational structure were obtained for this molecular system, the CaO spectra in air also represent a structured pseudo-continuum, the shape of which is almost impossible for modelling. Therefore, in this case, the presence of reference laboratory spectra is also necessary. We have obtained CaO spectra by evaporation of high-purity calcium carbonate (99.995%) to avoid any spectral interference. In contrast to iron, in this case, such a significant drop in the relative intensity of molecular bands is not observed at moderate pressures. In this case, at the lowest pressures, the total intensity of the spectra sharply decreases, which is due to the fact that the expansion of the plasma ceases to be constrained by the atmospheric pressure. Based on these observations, it can be assumed that CaO is formed at the flame periphery as a result of the interaction of atoms (ions) of the vaporized substance with atmospheric oxygen. The relative intensity of the CaO molecular bands increases monotonically with pressure, while the relative intensity of FeO reaches its maximum value at the minimum pressure. The resulting character of the dependence unambiguously indicates a different source of the formation of molecular forms in plasma, but the exact determination of the mechanism requires additional research. Both thermodynamic and kinetic studies of chemical reactions with the participation of iron-containing compounds formed in meteoric phenomena observed in the Earth's atmosphere has been carried out [1,3,6]. It is shown that the equilibrium chemical composition of the impact-generated cloud of atomic-molecular gas is achieved during the most intense luminescence of the optical bands of metal oxides AlO, MgO, CaO and FeO at altitudes of 20-40 km. The equilibrium content of the main chemical compounds in the formed meteoroid cloud as a function of temperature and atmospheric pressure is calculated. The thermodynamic, kinetic, and hydrodynamic conditions for the appearance of the airglow of orange iron oxide bands in the meteorite layer in the Earth's upper atmosphere are considered. From a comparison of the cooling time of the laser-formed cloud with the characteristic times of the the relevant chemical reactions, it was concluded that during the air-glow of the orange bands of FeO, the chemical composition of the shock-heating cloud corresponds to a local thermodynamic equilibrium (LTE). The temperature of FeO molecules was estimated using a decay of intensity of the laboratory emission spectra of the FeO orange system. The resulting estimates are found to be noticeably lower than the electron temperature of meta-stable Fe atoms. This was explained by the increased content of FeO molecules in the colder regions of the laser ablation cloud. The appearance of a broad peak in the 620-640 nm region upon cooling of the laser-ablation cloud at atmospheric pressure was associated with the formation of molecules of higher iron oxides. The systematic mass-spectroscopic experiments were carried out to analyze the products of photo-reactions induced by pulsed KrF laser radiation in a multi-layer coating of adsorbed benzene, methanol and dimethyl sulfoxide molecules (the latter molecule was chosen as a "model" one). The dependence of the yield of physically desorbed molecules and primary photofragments on the energy density of laser radiation are measured. All derived empirical dependences are described by the same power law, which responsible for the general mechanism of photolysis of adsorbed molecules through stepwise their excitation to a repulsive area of ​​ the potential energy surface, which asymptotically converges to a dissociation limit. A comparison of the present results with the literature data on the photolysis of molecules prepared in a molecular beam is performed. It has been shown that a binary collision between a photofragment and the rest adsorbed molecules, which occurs during the desorption of the first of the multilayer coating, determines the mechanism of photosynthesis of new compounds upon UV irradiation of the adsorbed surface. This mechanism, where only one of the reagents is created during the photolysis of an adsorbed molecule, seems to be the most relevant to a photochemistry on the surface of cosmic dust under the impact of the UV radiation in ISM [5]. Due to this process, the complex organic compounds are observed in molecular clouds where the simplest molecules and atoms ("precursors") from the highly diluted gas phase of the ISM are deposited on the surface of cosmic dust [4]. A comparative analysis of the results obtained for mono-layer and multi-layer coatings was carried out. Two most general mechanisms of photolysis were identified, and the features of photochemical processes for adsorbed molecules were formulated [2]. It is shown that photolysis of molecules on the surface of cosmic dust is relevant only in a limited wavelength range of the UV spectrum, which coincides with the energies of electronic transitions from the equilibrium ground state of a molecule to the repulsive branch of its electronically excited state. This restriction explains the relatively high photostability of adsorbed molecules in comparison with their gas-phase counterparts. The necessity is demonstrated to take into account microelectronic defects and in homogeneity of the adsorbent surface, leading to a decrease in the quantum yield of photolysis due to extremely rapid electronic-vibrational deactivation of excited states of adsorbed molecules and to an increase in the intensity of the local light field acting on the molecules, respectively. For the first few excited singlet and triplet states of the CO molecule, high-level quantum-chemical methods were applied for calculating the potential energy curves and dipole moments of spin-allowed and intercombination (spin-forbidden) molecular transitions to the ground singlet state of the molecule in a fully relativistic and scalar-relativistic approximation [4]. Under the scalar-relativistic approximation, electronic non-adiabatic matrix elements of the spin-orbit and electron-rotational interactions are obtained (in the framework of non-degenerated perturbation theory) as a parametric function of the internuclear distance. The sensitivity coefficients of electronic excitation energies and dipole moments for astrophysically important A1Pi-X1Sigma + and a3Pi-X1Sigma + transitions of the CO molecule to a possible variation of the fine structure constant alpha on a cosmological time scale are determined from first principle calculations. It is shown that the most sensitivity corresponds to rather narrow regions of internuclear distances localized near the crossing points of the singlet and triplet terms of the molecule. For particular rovibronic levels of both A1Pi- and a3Pi states, the radiative lifetimes are calculated, which are in good agreement with the results of precision measurements. From a comparative analysis of the rotational line positions of the different ArH+ isotopomers, measured in the laboratory and extracted from the adsorption spectra of quasars with a large redshift z an upper limit of the possible change in the ratio of the electron mass to the proton mass was established over the past 6-7 billion years [7].

 

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Annotation of the results obtained in 2018
The emission of the orange system of FeO in the range of 540-650 nm with laser-induced ablation of iron was first studied. It is shown that at reduction of plasma temperature in ~ 2 times – from 6400 K at 10 μs to 3100 K at 50 μs – the structure of emission spectra of iron monooxide is strongly changed, while intensive lines of atomic iron are observed for delays of 10-20 μs. Molecular spectra FeO well explain the nature of continuous intensive background radiation in laser ablation of steels at later times of observation. Unfortunately, there is no detailed classification of all observed spectra except at 591 and 611 nm. The comparison of the obtained spectra with the literary data showed a significant difference between them. It is supposed that spectra of laser plasma at temperatures more than 2000 K will be better to describe the processes observed in atmosphere of ablation of meteorites. Based on a comparative analysis of the literature data, an expert assessment of the current capabilities of ab initio quantum chemical modeling of the chemical evolution of the Universe was carried out. It has been established that the high level first principles calculations on the electronic structure of isolated molecules can play a key role in obtaining reliable data on the energy, radiation, magnetic and electrical properties, chemical network and interaction with cosmic radiation of molecular components observed in astronomical objects. In fact, multi-component chemical analysis of the atmosphere of the planets of the Solar System, exoplanets, comets, meteorites, cold stars, various ISM fractions, including cosmic dust is impossible without quantum-chemical modeling of the entire properties of their molecular compounds [1]. The photofragmentation of the simplest aromatic hydrocarbons (benzene, toluene, and chlorobenzene) physically adsorbed on the fused quartz surface under the UV radiation from a excimer KrF impulse laser have been experimentally studied [2]. Mass-spectrometric measurements were carried out in conditions, approaching typical environmental conditions of the ISM, and had the eventual goal to simulate the photochemistry of aromatic molecules adsorbed on the cosmic dust surface under their intense irradiation of the emerging massive stars. The signals of the quadrupole mass spectrometer were recorded under ultrahigh vacuum conditions, depending on the energy density of the laser radiation. It turned out that the photochemistry of adsorbed molecules is fundamentally different from the mechanisms of photoinduced processes that occur with isolated (desorbed) molecules in the gas phase. In particular, a three-photon dependence of the formation rate for desorption fragments was found with the dominant contribution of atomic hydrogen and phenyl radical, as well as neutral molecules of acetylene and ethylene, which appearance is caused by the cleavage of the carbon ring. The powerful UV laser radiation leads to the formation of surface defects and a network of micro cracks on the quartz, which is observed by an optical microscope. Similar photo desorption, apparently, occur in the ISM when exposed to the dust surface of cosmic rays as well as short-wave electromagnetic radiation. The laboratory mass spectrometric studies of laser-induced dissociation of the simplest aromatic hydrocarbons adsorbed on a quartz substrate under high vacuum and low temperatures were adapted to the ISM conditions corresponding to active star formation in dense clouds [3]. Impact of different surface photoprocesses, which are not taken into account in modern astrochemical models, on modeling of molecular evolution in protoplanetary disk has been studied in details. It has been shown that the main role in the photodesorption is played by the vibronic relaxation due to the straightforward transfer of the internal energy of overexcited molecules to the phonon energy of the solid. It is also possible that electronic deactivation of excited molecules takes place with the help of surface defects and an increase in the intensity of UV absorption due to local amplification of the electromagnetic field near the surface defects. It has been established that effects related to distinct features of adsorbed molecule photochemistry may change abundances of organic molecules by more than an order of magnitude [4]. In the framework of the fully relativistic approximation, highly accurate ab initio calculations on the electronic structure for low-lying singlet and triplet states of carbon monoxide were performed. For this, a multi-reference configuration interaction method (MRCI) was used. The derived estimates of the excitation energy, the electronic matrix elements of the spin-orbit splitting, and the intercombination transition dipole moments coincided with their empirical counterparts with the accuracy required for further predicting the dependence of the observed energy and radiation properties of the CO excited states to the possible variation of the fundamental physical constants on a cosmological time scale.

 

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Annotation of the results obtained in 2019
• The properties of the orange band system of FeO molecule were compared in the Beneshov bolide spectra measured at altitudes of 26, 29, 36, 39, 48 and 71 km and the Chechtice bolide on the 42 km highs. The relative radiation intensity of the main FeO bands does not change monotonously with a decrease in a height. This means that the meteor spectra are not sufficient to distinguish the electronic, vibrational and rotational temperature of FeO molecules. A detailed study of physical and chemical processes in the laser-educated cloud was carried out. Based on the available data on chemical reaction constants, the characteristic times of major chemical reactions involving iron-containing compounds in a laser-formed hot cloud are assessed. The time evolution of the spectrums of the orange FeO band system, obtained by laser-induced breakdown spectroscopy, was carried out and the temperature evolution of the FeO orange bands was studied. It is shown that at intermediate temperatures of laser-induced laboratory spectrums are well aligned with their meteor counterparts, and at the final temperatures with literary spectrums of reaction of chemiluminescence Fe+N2O. The peculiarities of the intensity distribution of in both laboratory spectrums are explained by the appearance of FeO2 at the final observation. • There are indisputable astronomical evidences to believe that the synthesis and destruc-tion of molecular compounds on the surface of cosmic dust, initiated by the interaction of the dust grain and/or the ice mantle adsorbed on it with cosmic radiation, are the key factors of the chemical evolution of the Universe on a cosmological time scale. The cosmic dust grain, that consists mainly of carbonaceous and silicate compounds, turns out to be not only a unique “astrochemical” reactor for photosynthesis of complex organic molecules, but also a place for their survival under harsh ISM conditions. The photo-induced reactions also create the molecular environment of young planetary systems, in particular, the proto-Solar system. The multistage processes associated with the adsorption of atoms and molecules from the gas phase of the ISM, their drift on the dust surface, heterogeneous catalysis, radiolysis, photolysis and desorption of the final products, as well as the chemical evolution of dust grain itself, should be taken into account in advance astrochemical models. The photofragmentation of methanol molecules in a physisorbed monolayer on the cooled silica surface under the UV irradiation by a pulsed excimer KrF laser have been experimentally studied. The rupture of all kinds of molecular bonds in methanol, namely, C-O, O-H, and C-H has been found. As a result of the photodissociation, H atom as well as OH, CH3 and CH3O radicals desorbs from the surface and react to each other both on the surface and nearby. The experiments with partially deuterated methanol molecules have demonstrated that H atoms are originated from both hydroxyl and methyl groups of the molecule. The ratios of photofragments have been measured; they differ from the ratios received for methanol molecular beams and ices under VUV irradiation. No H2 and СH4 molecules have been detected due to restricted isomerization of adsorbed molecules and low surface concentrations of molecules in the monolayer with the coverage about 0.1. • A procedure of converting the results of fully relativistic all-electron multireference configuration interaction (MRCI) electronic structure calculation into effective spin-orbit interactions and spin-independent interatomic potentials for low-lying diatomic electronic states has been developed. The procedure is based on the adaptation of the projection technique [A Zaitsevskii et al., Phys. Rev. A 96, 022516 (2017)] to the cases of relativistic four- or two-component description of molecular electronic subsystem without invoking the relativistic pseudopotential concept and MRCI representation of the wavefunction. Due to the smoothness and regularity of the resulting potential energy and spin-orbit coupling functions contrasting with the behavior of adiabatic potential surfaces produced by the relativistic MRCI calculations, the interpolation of data obtained and rovibronic state modeling are simplified. High level quantum-chemical calculations on the electronic structure of the CO molecule have been performed in the framework of pure "a" and "c" Hund’s coupling cases. In the result, potential energy curves (PECs) of the ground and low-lying excited electronic states of carbon monoxide were obtained together with the corresponding spin-orbit coupling matrix elements and dipole moment functions for spin-allowed and spin-forbidden electronic transitions. The fully relativistic model of the CO electron system was based on the Dirac-Coulomb-Gaunt approximation for the Hamiltonian which considered the fine structure constant α as a variable parameter and used the “exact” transformation to the two-component picture. To describe the electron correlation the large scale multi-reference configuration interaction (MRCI) method has been used. To monitor of the MRCI energy convergence the various compositions of reference wave function and active space were employed. Potential energy curves of the excited states were obtained by adding the vertical excitation energies as functions of the internuclear distance to the accurate empirical ground state PEC. The dependence of the fine structure rovibronic energies and transition dipole moments on the different values of the parameter α was studied in details. Therefore, both relativistic and mass effects could be treated simultaneously. https://istina.msu.ru/projects/110089584/

 

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