Atoms Of Heavy Elements Research Articles

Features of obtaining and properties of thin films organic semiconductors

In recent decades, thin films of organic semiconductors (OS), or, as they are also called, organic molecular crystals, have attracted special attention in connection with a number of proposals for their use in functional units of modern electronics, and therefore in modern technological equipment. At the same time, the optical, electrophysical and photoelectric properties of OS are very important, which are determined both by the structure of organic molecules, that is, the starting material, and by the crystal structure of condensates, that is, by the technological conditions of film production. In this regard, this article presents the results of studies of some properties of OS and the technology of obtaining thin films based on them. OS are characterized by weak intermolecular bonds of the Van der Baals type, which causes the low energy of their crystal lattice. In this regard, the electronic structure of individual molecules during the formation of a crystal does not change significantly, and the properties of the crystals almost completely preserve the individual features of the molecules in combination with new properties caused by their collective interaction. This determines the main features of optical and electrophysical properties of OS, their energy structure of neutral and ionized states. In this article, it is experimentally confirmed that the planar structure of atoms of molecular crystals, in particular, linear acenes, and therefore the number of π-electrons responsible for exciton absorption in the visible region of the spectrum determines the position of the edge of their own optical absorption. It was also confirmed that the long-wavelength shift of the optical absorption edge of thin films of phthalocyanines is observed when atoms of heavy elements, for example, lead, are introduced into the molecule. When atoms of lighter elements are introduced into the phthalocyanine molecule, their planarity is not disturbed, and the long-wavelength shift of the edge is much smaller. An explanation of such changes is presented based on the interaction of foreign atoms with the π-electron system of phthalocyanine rings of neighboring molecules. The significant influence of the technological parameters of production, in particular the temperature of the substrate during thermal sputtering, on the crystal structure and optical properties of thin films of linear polyacenes and metallophthalocyanines has been demonstrated and substantiated. The possibility of controlling and presetting the necessary properties of thin-film condensates of molecular crystals is shown.

Dynamic Mapping of Effective Nuclear Charge for 1S1/2-Shell Electrons and Nominal Nuclear Charge for Heavy Element Atoms with 10 ≤ Z ≤ 173

Dynamic Mapping of Effective Nuclear Charge for 1S1/2-Shell Electrons and Nominal Nuclear Charge for Heavy Element Atoms with 10 ≤ Z ≤ 173

Динамическое отображение эффективного заряда ядра для электронов 1S1/2-оболочек и номинального заряда ядра для атомов тяжелых элементов с 10 ≤ Z ≤ 173

Динамическое отображение эффективного заряда ядра для электронов 1S1/2-оболочек и номинального заряда ядра для атомов тяжелых элементов с 10 ≤ Z ≤ 173

Use of β Radiation to Localize the Binding Sites of Mercury Ions and Platinum-Containing Ligand in DNA

Composite sequence-specific ligands with DNA-damaging groups may dramatically increase the efficacy of radiotherapy. The most promising damage sensitizers are the atoms of heavy elements, in which electrons are emitted from upper orbitals and a multiply charged positive ion forms when an electron is kicked out from lower orbitals. The biophysical mechanisms of DNA damage produced by these sensitizers are far from fully understood. In this work, high-performance polyacrylamide gel electrophoresis (PAGE) in denaturing gel was used to investigate the nature of DNA cleavage on exposure to β radiation for complexes of heavy atom-containing ligands with DNA restriction fragments. It was demonstrated for the first time that DNA in complexes with Pt-bis-netropsin or mercury salts is cleaved in the vicinity of the heavy atom in the presence of radioactive isotopes emitting β particles of different energies. In the presence of 1 M glycerol, the cleavage of the DNA sugar-phosphate backbone was almost entirely due to a neutralization of the multiply charged Auger ion and was not associated with the Auger electron electron-beam radiolysis. Based on the observations, a relatively simple technique was proposed for precise localization of binding sites for various DNA ligands containing a heavy atom. Analysis of the end groups at the cleavage point and the nature of damage to the complementary DNA chain made it possible to speculate about the mechanisms of direct influence of irradiation on a heavy atom.

Diagnostics for the elemental composition of protostellar objects

The sensitivity of a number of aspects of the chemical evolution of a molecular cloud to its elemental composition is investigated. Four models are considered: one with high metallicity, for which the evolution proceeds exclusively in the gas phase, two with low metallicity, for which processes proceed both in the gas phase and on grain surfaces, and a model with low metallicity and an artificially reduced oxygen content. One of the low-metallicity models initially contains only neutral components, while some initial ionization of atoms of heavy elements is included in the other models. A network of chemical reactions, including a detailed description of the chemistry of deuterium compounds, is used to analyze this sensitivity. It is shown that the initial composition affects the chemical evolution of most components in some way, but this influence is sometimes negligible. The inclusion of certain chemical factors can be important, such as surface reactions and the loss of a substantial fraction of atoms of heavy elements that are in grains. However, some components are influenced by even small variations in the initial and elemental compositions. One such component is the DCO+ ion, whose evolution is sensitive to the initial degree of ionization of atoms of heavy elements, even if the set of reactions included and the elemental composition are the same in different cases. The possible use of HD and HF as indicators of the presence of molecular hydrogen is also considered. HF reliably traces H2 at times exceeding 105 years under the physical conditions considered. However,HD is not a reliable indicator of H2 at the densities characteristic for protostellar clouds.

Heavy Element Effects in the Diagonal Born-Oppenheimer Correction within a Relativistic Spin-Free Hamiltonian.

Methodologies beyond the Born-Oppenheimer (BO) approximation are nowadays important to explain high precision spectroscopic measurements. Most previous evaluations of the BO correction are, however, focused on light-element molecules and based on a nonrelativistic Hamiltonian, so no information about the BO approximation (BOA) breakdown in heavy-element molecules is available. The present work is the first to investigate the BOA breakdown for the entire periodic table, by considering scalar relativistic effects in the Diagonal BO correction (DBOC). In closed shell atoms, the relativistic EDBOC scales as Z(1.25) and the nonrelativistic EDBOC scales as Z(1.17), where Z is the atomic number. Hence, we found that EDBOC becomes larger in heavy element atoms and molecules, and the relativistic EDBOC increases faster than nonrelativistic EDBOC. We have further investigated the DBOC effects on properties such as potential energy curves, spectroscopic parameters, and various energetic properties. The DBOC effects for these properties are mostly affected by the lightest atom in the molecule. Hence, in X2 or XAt molecule (X = H, Li, Na, K, Rb, and Cs) the effect of DBOC systematically decreases when X becomes heavier but in HX molecules, the effect of DBOC seems relatively similar among all the molecules.

Effective charge of the nucleus for 2s 1/2- and 2p 1/2-shells in atoms of heavy elements

Effective nucleus charges Z eff are calculated for electrons of 2s 1/2- and 2p 1/2-shells in atoms of heavy elements with the use of the Dirac–Sommerfeld relativistic formula. It is established that starting from Z = 87, a change of ∆Z eff > 1 is observed when going to the subsequent element (∆Z = 1), that is, anti-screening of a certain type takes place.

Mechanism of formation and monomolecular decomposition of aci-nitromethanes: a quantum-chemical study

A quantum-chemical study of the reactions of formation of aci-nitromethane (aci-NM) and aci-dinitromethane (aci-DNM) and their decomposition with elimination of water was carried out. The methods employed were the ab initio RHF method with inclusion of electron correlation at the MP2 level of theory and the Dunning—Hay double zeta basis set augmented with polarization d-functions on heavy-element atoms, the DFT approach at the B3LYP level, and the semiempirical PM3 method. The formation of aci-NM and aci-DNM was found to be the limiting stage of the mechanism under study. For DNM, the barrier to reaction is substantially lower than for NM. The estimates of the heights of the barriers to formation found from density functional calculations at the B3LYP/6-311++G(df,p) level (258 kJ mol–1 for aci-NM and 218.5 kJ mol–1 for aci-DNM) are thought to be the most reliable.

Identification of the anomalous 26.131-MHz nitrogen line observed towards Cas A

Konovalenko and Sodin1 recently reported the detection of an absorption line at a frequency of 26.131 MHz towards Cassiopeia A and attributed the line to the 26.127 MHz F = 5/2 → 3/2 hyperfine transition of 14N. The difference in frequency corresponds to a radial velocity of –40 km s–1, which is compatible with the mean velocity of the Perseus arm H I absorption lines seen towards Cas A. However, to explain the strength of the line, Konovalenko and Sodin require (N/H) = 8 × 10–3 compared with the cosmic ratio of 1.2 × 10–4. An anomalous abundance of this magnitude would have substantial impact on ideas about galactic nucleosynthesis. We suggest here that the line is a 631α recombination line due to neutral atoms of heavy elements—either carbon atoms in the H I clouds or possibly heavier atoms (Mg, Ca, Fe) in hot (∼104 K) ionized gas along the line of sight to Cas A.