Pyrite oxidation: a state-of-the-art assessment of the reaction mechanism

The oxidation of pyrite to release ferrous iron and sulfate ions to solution involves the transfer of seven electrons from each sulfur atom in the mineral to an aqueous oxidant. Because only one or, at most, two electrons can be transferred at a time, the overall oxidation process is quite complex. Furthermore, pyrite is a semiconductor, so the electrons are transferred from sulfur atoms at an anodic site, where oxygen atoms from water molecules attach to the sulfur atoms to form sulfoxy species, through the crystal to cathodic Fe(II) sites, where they are acquired by the oxidant species. The reaction at the cathodic sites is the rate-determining step for the overall process. This paper maps out the most important steps in this overall process.     

Collision-induced absorption of radiation in the atmospheres of late-type stars

Problems associated with taking into account absorption induced by collisions between hydrogen and helium atoms, helium atoms and hydrogen molecules, and hydrogen molecules, resulting in the formation of short-lived, quasi-molecular complexes are discussed, together with opacity in the atmospheres of late-type stars due to such absorption. There is good agreement between such opacities computed using codes developed by the author and by R. Kurucz. To demonstrate the importance of including collision-induced opacity, theoretical fluxes are compared to the observed spectral energy distribution of the metal-poor L subdwarf SDSS J125637.13-022452.4. The spectral energy distribution of this object can be reproduced with an effective temperature of T_eff = 2600 K only if collision-induced absorption is taken into account.     

Processes of the development of the molecular world at early stages of its formation: Evidence from the investigation of the behavior of the vibrational entropy of molecules

We analyzed the possibility of explaining empirical relations in the evolution of the molecular world on the basis of fundamental physical laws and theories of the behavior of the entropy of a system. Quantitative expressions were evaluated describing the entropy of internal motion of atoms in a molecular ensemble (vibrational entropy), which is a term of total entropy with a clear physical meaning. It was shown that vibrational entropy is controlled primarily by the structure of the compound rather than the number and identity of atoms in the molecule. During the early stages of evolution, the appearance of acyclic structures is more advantageous than that of cyclic structures. An increase in the complexity of the molecular world inevitably leads to the appearance of molecules with a complex skeleton formed mainly by bonds of the same elasticity as C–C. The necessity of helical structures, whose spatial elasticity is provided by hydrogen bonds, was explained.     

Chemodynamical evolution of gas near an expanding HII region

A self-consistent model for the chemical-dynamical evolution of a region of ionized hydrogen around a massive young star and of the surrounding molecular gas is presented. The model includes all main chemical and physical processes, namely the photoionization of atomic hydrogen, photodissociation of molecular hydrogen and other molecules, and the evaporation of molecules from the mantles of dust particles. Heating and cooling processes are taken into account in the temperature calculations, including cooling in molecular and atomic lines. The hydrodynamical equations were solved using the Zeus2D hydrodynamical software package. This model is used to analyze the expansion of a region of ionized hydrogen around massive stars (effective temperature of 30 000 and 40 000 K) in a medium with various initial density distributions. The competition between evaporation from dust mantles and the photodissociation of molecules results in the formation of a transition layer between the hot HII region and cool quiescent medium, characterized by high abundances of molecules in the gas phase. The thickness of the transition layer is different for different molecules. Since there is a velocity gradient along the transition layer, and the maxima in the distributions of different molecules are at different distances from the star, observations of molecular emission lines should reveal distinction in shifts of lines of different molecules relative to the velocity of the quiescent gas. Such shifts have indeed been detected during molecular observations of the region of ionized hydrogen Sh2-235. For an initial gas density of 10³ cm^?3, the increase in the abundances of H₂O and H₂CO in the transition layer after desorption from dust occurs gradually rather than in a jump-like fashion; therefore, the concept of a “evaporation front” can be used only formally. In addition, the distances between the evaporation fronts for different molecules are significant. At higher initial gas densities (10⁴ cm^?3), sharp evaporation fronts are formed for the different molecules, which are close to each other and to the shock front. In this case, it is possible to speak of a single evaporation front for CO, H₂O, and H₂CO.     

The quantum matrix and information from the hydrocarbon oil molecule

The quantum matrix of the hydrocarbon (HC) molecule is substantiated. On the basis of its properties and behavior, the genesis of oil is explained as a process of self-evolution of oil and preservation of molecules of different composition and generation time. Individual HC molecules are generated in nanoseconds, and the period of the genesis of oil is comparable with that of migration of the HC fluid from the mantle to the deposit. A model of subatomic abiogenic genesis of oil is presented. Hydrocarbon (HC) molecules of various structure and composition are formed due to interaction of the valency electron orbitals of C and H atoms, the elemental particles of which are quantum objects and carriers of information. On the basis of this, the term quantum matrix of the HC molecule, the properties and behavior of which explain the genesis of oil as a process of its self-evolution and preservation of the molecules of various composition and the period of generation of oil, is substantiated. It is proved that individual HC molecules are generated within nanoseconds and the period of origin of the entire assemblage of more than 500 molecules of oil of various types is comparable with the period of migration of the HC fluid from the mantle to the deposit.     

The Photolysis of Aromatic Hydrocarbons Adsorbed on the Surfaces of Cosmic Dust Grains

The results of laboratory mass-spectrometer studies of the laser-induced dissociation of molecules of simple aromatic hydrocarbons adsorbed on a quartz substrate under the conditions of deep vacuum and low temperatures are adapted to the physical and chemical conditions in regions of active star formation in molecular clouds. The main properties of the photolysis of physically adsorbed molecules compared to the photodissociation of isolated molecules in the gas phase are identified. The relevance of molecular photolytic desorption to the real conditions in the interstellar medium is analyzed, in particular, to the conditions in photodissociation regions. It is shown that the photodissociation of adsorbed benzene occurs along other channels and with appreciably lower efficiency than does the corresponding process in the gas phase. The photodissociation of aromatic hydrocarbons adsorbed on the surfaces of interstellar grains cannot make a large contribution to the abundance of hydrocarbons with small numbers of atoms observed in the interstellar medium.

     

Ab initio quantum chemical investigation of arsenic sulfide molecular diversity from As4S6 and As4

The structural diversity of arsenic sulfide molecules in compositions between As₄S₆ and As₄ was investigated using ab initio quantum chemical calculations. The As₄S₆ molecule consists of four trigonal pyramid coordinations of As atoms bonding to three S atoms. In the As₄S₅ composition, only one type of molecular configuration corresponds to an uzonite-type molecule. In the As₄S₄ composition, two molecular configurations exist with realgar-type and pararealgar-type molecules. Three molecular configurations are in the As₄S₃ composition. The first configuration comprises trigonal pyramidal As atom coordinations of two types: bonding to two S atoms and one As atom, and bonding to one S atom and two As atoms. The second is the molecular configuration of dimorphite. The third comprises trigonal pyramidal As atom coordinations of two types: bonding to three As atoms, and bonding to one As atom and two S atoms. The As₄S₂ composition allows molecular configurations of two types. One is comprised of trigonal pyramidal As atom configurations of one type bonding to two As atoms and one S atom. The other comprises trigonal pyramidal As atom coordinations of three types: bonding to two S atoms and one As atoms, bonding to one S atom and two As atoms, and bonding to three As atoms. The As₄S molecule has trigonal pyramidal As atom coordinations of two types: bonding to one S atom and two As atoms, and bonding to three As atoms. The As₄S composition permits only one molecular configuration, which suggests that the mineral duranusite comprises the As₄S molecular geometry. In all, ten molecular configurations are predicted in the molecular hierarchy of the arsenic sulfide binary system. The simulated Raman spectral profiles are helpful in searching for undiscovered arsenic sulfide minerals.     

New homologous series of biomarker molecules from Vendian deposits of the Sayan-adjacent Biryusa area

We studied the organochemical distribution of saturated hydrocarbons in organic matter of mudstones of the Vendian Marna Formation in the Sayan-adjacent Biryusa area. The formation is composed of glacial, glacio-alluvial, and lacustrine deposits.In the fraction of saturated hydrocarbons in chloroform extracts (bitumoids), a homologous series of earlier unknown 2,7-dimethyl alkanes has been identified, with molecules having the even number of carbon atoms prevailing. The possible sources of such abundant biomarkers are considered.     

Bond length variation in hydronitride molecules and nitride crystals

Bond lengths calculated for the coordination polyhedra in hydronitride molecules match average values observed for XN bonds involving main group X-cations in nitride crystals to within 0.04 Å. As suggested for oxide and sulfide molecules and crystals, the forces that determine the average bond lengths recorded for coordinated polyhedra in hydronitride molecules and nitride crystals appear to be governed in large part by the atoms that comprise the polyhedra and those that induce local charge balance. The forces exerted on the coordinated polyhedra by other parts of the structure seem to play a small if not an insignificant role in governing bond length variations. Bonded radii for the nitride ion obtained from theoretical electron density maps calculated for the molecules increase linearly with bond length as observed for nitride crystals with the rock salt structure. Promolecule radii calculated for the molecules correlate with bonded and ionic radii, indicating that the electron density distributions in hydronitride molecules possess a significant atomic component, despite bond type.     

Time evolution of twin domains in cordierite: a computer simulation study

The time and temperature evolution of twinning in cordierite is simulated using three computer models. The orientation of walls between twin domains in natural cordierite follows mainly the ferroelastic pattern which minimises the strain energy of the walls between twin-related domains. Such ferroelastic twinning is simulated in an elastic three-states Potts model in which each structural six-membered ring is represented by a three state pseudo-spin. The resulting twin pattern in a sample with 3169 structural rings shows sector trilling and fine scale ferroelastic wall patterns which coarsen with increasing annealing time. The poorly defined wall directions observed in cordierite were found to be related to twin walls which do not minimise the strain energy. Instead, these walls are located along the corners of pseudo-hexagonal rings and appear as the consequence of local rather than global interatomic interactions. Simulations using two-dimensional (38028 atoms) and three-dimensional (408 228 atoms) structural models show a predominance of these topological walls over the strain walls at early stages in the ordering process. The domain structure in the simulation is patchy rather than corresponding to repeated stripe structures found in other ferroelastic and co-elastic materials. In all models, a strong tendency for sector trilling is observed. In kinetic tweed patterns a novel 60o tweed is found at atomic length scales while the usual strain-mediated 90o tweed appears at mesoscopic length scales. An unusual surface tension effect in domain formation and ’writhing’, fluid-like motion was found in the three-dimensional structural model. This motion, along with the existence of non strain-mediated walls may contribute to cordierite’s poorly defined domain wall directions at the early stages of domain coarsening. Received: 11 March 1998 / Revised, accepted: 28 August 1998     

Molecular modeling of water structure in nano-pores between brucite (001) surfaces

Molecular dynamics (MD) computer simulations of liquid water held in one-dimensional nano-confinement by two parallel, electrostatically neutral but hydrophilic surfaces of brucite, Mg(OH)₂, provide greatly increased, atomistically detailed understanding of surface-related effects on the spatial variation in the structural ordering, hydrogen bond (H-bond) organization, and local density of H₂O molecules at this important model hydroxide surface. NVT-ensemble MD simulations (i.e., at constant number of atoms, volume and temperature) were performed for a series of model systems consisting of 3 to 30 Å-thick water layers (containing 35 to 360 H₂O molecules) confined between two 19 Å-thick brucite substrate layers. The results show that the hydrophilic substrate significantly influences the near-surface water structure, with both H-bond donation to the surface oxygen atoms and H-bond acceptance from the surface hydrogen atoms in the first surface layer of H₂O molecules playing key roles. Profiles of oxygen and hydrogen atomic density and H₂O dipole orientation show significant deviation from the corresponding structural properties of bulk water to distances as large as 15 Å (∼5 molecular water layers) from the surface, with the local structural environment varying significantly with the distance from the surface. The water molecules in the first layer at about 2.45 Å from the surface have a two-dimensional hexagonal arrangement parallel to brucite layers, reflecting the brucite surface structure, have total nearest neighbor coordinations of 5 or 6, and are significantly limited in their position and orientation. The greatest degree of the tetrahedral (ice-like) ordering occurs at about 4 Å from the surface. The translational and orientational ordering of H₂O molecules in layers further from the surface become progressively more similar to those of bulk liquid water. A quantitative statistical analysis of the MD-generated instantaneous molecular configurations in terms of local density, molecular orientation, nearest neighbor coordination, and the structural details of the H-bonding network shows that the local structure of interfacial water at the brucite surface results from a combination of “hard wall” (geometric and confinement) effects, highly directional H-bonding, and thermal motion. This structure does not resemble that of bulk water at ambient conditions or at elevated or reduced temperature, but shares some similarities with that of water under higher pressure.     

Fracture induced emission of alkali atoms from feldspar

Emission of neutral atoms (K and Na) and molecules (H₂O and KOH) observed during fracture of K-feldspar have been accounted for by two independent mechanisms. H₂O and KOH emissions are attributed to the venting of fluid-filled inclusions, while emission of atomic K is due to surface effects accompanying cleavage of crystalline feldspar. The intensity of emitted potassium, at least 6 × 10¹⁴ atoms/cm² of surface area, is sufficient to affect K activities in solution during microbrecciation in the presence of rock-dominated fluids.     

Frequency dependence of the evolution of the radio emission of the supernova remnant Cas A

Many-year measurements of the radio flux of the young supernova remnant Cassiopeia A relative to the radio galaxy Cygnus A were continued at 290 and 151.5 MHz. The new data are used together with previously published observations carried out at decameter, meter, centimeter, and millimeter wavelengths to derive the frequency dependence of the secular variation of the radio flux density of Cas A: $d_\nu [\% year^{ - 1} ] = - (0.63 \pm 0.02) + (0.04 \pm 0.01)\ln \nu [GHz] + (1.51 \pm 0.16) \times 10^{ - 5} (\nu [GHz])^{ - 2.1} $ . The observed slowing of the secular variations with decreasing frequency at decameter wavelengths can be explained by a decrease in the optical depth of a remnant HII zone around Cas A with time due to recombination of hydrogen atoms. The new derived frequency dependence for the rate of the secular decrease, absolute and relative measurements of the radio flux density of Cas A carried out over the last 25 years, and the absolute spectrum of Cyg A are used to construct the spectrum of Cas A in the range 5–250 000 MHz predicted for epoch 2015.5.     

孔道结构化合物(H3NCH2CH2NH3)3[(VO)4(PO4)2(HPO4)4]的钒氧化态与热稳定性关系研究

热处理脱除有机模板易导致VPO体系孔道结构化合物结构破坏,从而阻碍此类材料的实际应用。以孔道结构化合物(H3NCH2CH2NH3)3[(VO)4 (PO4 )2 (HPO4 )4 ](简称V2P3 en)为研究对象,利用热分析(DSC TG)、动态原位高温X 射线衍射(XRD)及多功能X 射线光电子能谱(XPS)等方法,研究了该化合物在不同气氛热处理过程中模板脱除及结构演化规律,重点探讨了钒氧化态的变化对结构稳定性的影响。结果表明,加热过程中随着有机模板的分解脱除,形成较强的还原环境,骨架中的部分钒被还原(V4+→V3+),使原有的配位环境([VⅣO5]三角双锥、[VⅣO6]畸变八面体)与钒的氧化态不符而导致结构重组。因此,钒氧化态的变化是影响热稳定性的重要因素之一。     

真实自回避行走中晶体生长界面结构的分形行为

晶体生长过程实际上就是生长基元从周围环境中不断地通过界面而进入晶格座位的过程。一般认为,研究生长基元以何种方式以及如何通过界面进入晶格座位是晶体生长界面结构研究中的关键。在生长基元以分子或者原子的微粒子形式在生长环境中进行无规游走的前提下,本文运用真实自回避行走(TSAW)模型,通过重整化群思想来研究晶体生长界面结构的分形行为。研究发现:晶体生长界面结构的分形行为与生长基元的游走路径形态密切相关,并且在理想状况下真实自回避行走与标准Koch曲线的分形维极为接近。     

Impact of the desorption energy of atomic oxygen on the chemical evolution in star-forming regions

The impact of a recently measured values of the desorption energy of oxygen released from the surface of silicate dust particles on the results of numerical simulations is analyzed. The chemical evolution of the interstellar medium under conditions corresponding to those in a cold, dark cloud is considered, together with the collapse of a translucent cloud into a dark cloud. Astrochemical modeling methods are used to show that, overall, there were no substantial changes in the chemical evolution under the conditions for the selected models for these objects, but the formation of somemolecules is sensitive to the change from the traditionally adopted oxygen desorption energy (800 K) to the new value (1850 K). The characteristics of the formation of such molecules are analyzed.     

岩矿分析与经典法

回顾了近一个世纪以来经典的湿化学法（重量法和容量法）在岩矿分析方面的建立、发展情况。认为：经典法曾有过长期的持续发展，对地学研究有过巨大的贡献，但由于地学研究对象主要转移至痕量元素以及经典法不适合痕量分析，在一些以仪器分析为主要手段的实验室，有被取代的现象。指出：由于经典法依据的是全部原子、离子或分子参与的不可逆反应，是能够直接溯源至SI基本测量单位的分析技术，其优点为绝大多数仪器技术所不及，因此，它可以在某些领域被淡忘，但是不会消亡。     

Spectropolarimetric Observations of Magnetic White Dwarfs with the SAO 6-m Telescope

The results of spectropolarimetric observations of a number of magnetic white dwarfs obtained on the 6-m optical telescope of the Special Astrophysical Observatory are presented. The observations were carried out using the SCORPIO focal aperture-ratio reducer in a spectropolarimetric regime. Two characteristic dependences of the degree of polarization on the wavelength are observed. For one group of objects, the degree of linear polarization grows with wavelength, suggesting that the alignment of atoms and molecules in Rydberg states in the atmosphere of the white dwarf due to the action of its magnetic field influences scattering processes. The second group of objects displays an increase in the degrees of both linear and circular polarization with wavelength, providing evidence for the presence of protoplanetary disks around these magnetic white dwarfs, in which the alignment of circumstellar grains leads to the observed behavior.     

Naphthene-aromatic hydrocarbons in oils of different genesis

Naphthene-benzenes, naphthene-naphthalenes, and naphthene-phenantrenes have been extracted with methanol from mono-, bi-, and triarene fractions of oils of different genetic types from the West Siberian, Timan–Pechora, North Caucasian, and Pannonian (Serbia) oil-and-gas-bearing basins. The hydrocarbon composition and molecular-mass distribution (MMD) of naphthene-arenes have been determined by mass spectrometry. Naphthene-benzene and naphthene-naphthalene molecules contain one to six naphthenic cycles, whereas naphthene-phenantrene molecules contain one to three naphthenic rings. The number of carbon atoms in the alkyl groups of naphthene-benzenes, naphthene-naphthalenes, and naphthene-phenantrenes reaches 38, 20, and 19, respectively. Distinctive features of group compositions and MMD of naphthene-arenes have been revealed in oils generated by different organic matter.