Structures and properties of the tin-doped carbon clusters

A systemic density functional theory study of the tin-doped carbon clusters has been carried out using B3LYP method with TZP+ basis set. For each species, the electronic states, relative energies and geometries of various isomers are reported. Except for smaller SnC₂ and the largest , the Sn-terminated linear or quasi-linear isomer is the most stable structure for clusters. The electronic ground state is alternate between ³Σ (for n-odd member) and ¹Σ (for the n-even member) for linear SnC_n and invariably ²Π for linear and , except for SnC/SnC⁺/SnC⁻,, and . The incremental binding energy diagrams show that strong even–odd alternations in the cluster stability exist for both neutral SnC_n and anionic , with their n-even members being much more stable than the corresponding odd n − 1 and n + 1 ones, while for cationic , the alternation effect is less pronounced. These parity effects also reflect in the ionization potential and electron affinity curves. By comparing with the fragmentation energies accompanying various channels, the most favorable dissociation channel for each kind of the clusters are given. All these results are very similar to those obtained previously for the clusters.     

Vibrational relaxation on the mixed vibronic levels of the and states in all-trans-neurosporene as revealed by subpicosecond time-resolved, stimulated emission and transient absorption spectroscopy

In all-trans-neurosporene, whose level is lower than the level by one vibrational quantum, the following two steps of vibrational relaxation from the mixed vibronic states were identified, in the order, stimulated emission stimulated emission transient absorption. The stimulated emission patterns were simulated by the use of Franck–Condon factors in the transitions from the pair of mixed vibronic levels down to the ground vibronic levels. The vibronic levels of the mixed and state were characterized theoretically based on the diabatic approximation.     

Theoretical study on the structures and properties of LiCn, , and (n = 1–10) clusters

The lithium-doped carbon clusters LiC_n, , and (n = 1–10) have been investigated systemically with density functional theory (DFT) method at the B3LYP/6-311+G* level. According to the total energies of different kinds of isomers, the LiC_n, , and (n = 1–10) clusters have Li-terminated linear ground states structures, except for LiC₂, LiC₃, , and (n = 4–6). The incremental binding energies are evaluated to elucidate the stabilities of the clusters with different numbers of carbon atoms for neutral molecules, cations, and anions, respectively. Clear even–odd alternation effects are observed for the stability of the cationic clusters and anionic clusters, while for neutral LiC_n clusters the alternation effect is less pronounced. Similarly, the ionization potentials and electron affinities of LiC_n also express an obvious parity alternation. In addition, the most favorable dissociation channels are acquired according to the fragmentation energies accompanying various pathways.     

First principles study of the structure, electronic state and stability of cations

Structural and electronic properties of semiconductor binary microclusters cations have been investigated using the B3LYP-DFT method in the ranges of n=1, 2 and m=1–7. Full structural optimization, adiabatic ionization potentials calculation and frequency analysis are performed with the basis of 6-311+G(d). The charged-induced structural changes in these cations have been discussed. The strong As–As bond is also favored over Al–As bonds in the cations in comparison with corresponding neutral cluster. With As_m forming the base, adding Al atom(s) in different positions would find the stable structures of cations quickly and correctly. , , and are predicted to be species with high stabilities and possible to be produced experimentally.     

Ab initio electronic and rovibrational structure of

The electronic structure of the ground state of has been investigated using relativistically-corrected CCSD(T) in conjunction with ANO-RCC (Mg) and aug-cc-pVQZ (H) basis sets. The molecular potential energy surface possessed minima corresponding to both ¹A₁ and equilibrium structures (with a ¹Σ⁺ transition state). The ¹A₁ structure possessed R_e and θ_e values of 2.0297 Å and of 22.09°, respectively. The higher-energy structure exhibited an R_e value of 2.1658 Å. Property surfaces were constructed to calculate rovibrational energies and spectral line intensities for the ground states of , (¹A′) MgHD²⁺ and . For the vibration ground state of , the vibration-averaged R_e and θ_e values were calculated to be 2.0209 Å and 22.53°, respectively. The A, B and C rotational constants were calculated to be 58.0, 2.21 and 2.11 cm⁻¹, respectively.     

Unique charge ordering of manganese in a new mixed valent phosphate

A new mixed-valent manganese phosphate, , has been synthesized using hydrothermal method. Its monoclinic C2/c structure (a=12.5506(16) Å, b=10.4816(18) Å, c=13.6723(10) Å, β=103.758(11)°) forms a 3D framework of MnO₆ octahedra, MnO₅ trigonal bipyramids, PO₄ and PO₃OH tetrahedra. The main structural feature of this phosphate deals with its [Mn₄O₁₆]_∞ chains running along , which are interconnected through PO₄ and PO₃OH tetrahedra, forming intersecting tunnels running along [110], and [001]. The geometry of the [Mn₄O₁₆]_∞ chains and the charge ordering of manganese in the latter are unique: they consist of trimeric units of divalent manganese “” alternating with single trivalent Mn^IIIO₆ octahedra along . In each “” unit one central Mn^IIO₆ octahedron shares two opposite edges with two Mn^IIO₅ trigonal bipyramids. Along , one Mn(II) octahedron alternates with one Mn(III) octahedron by sharing one corner. The relationships between the structure of this unique charge ordered phosphate and other manganese phosphates are discussed.     

DFT study of electronic structure and geometry of anionic silver clusters (n = 11, 12, 17)

Based on both total energy calculations and comparison of experimental and calculated characteristics of photoelectron spectra (PHES), the structural assignment of clusters and has been made using DFT model with recently developed S2LYP functional. The calculated characteristics of PHES for the assigned structures are in excellent agreement with the experimental ones. The electronic structure, geometry and energetic characteristics of low-lying isomers have also been studied. The calculated geometrical parameters of and clusters as well as the geometries of earlier established clusters have been compared with the geometrical characteristics of anionic sodium clusters. The structures of anionic silver and sodium clusters have been found to be very similar. The difference has been observed only for . Based on similarity of the geometries of silver and sodium clusters as well as on the comparison of calculated and experimental characteristics of PHES, the geometry of cluster has been assigned.     

Auger recombination dynamics in clusters

Electronic relaxation dynamics following interband excitation from the 6s to the 6p band in mass selected clusters are measured through femtosecond time-resolved photoelectron imaging (TRPEI). This interband transition is pumped at 4.65 eV and probed at 1.55 eV. Auger decay of occurs on a timescale of 490 ± 100 fs, and a similar time constant is seen for the transient excited state population created by the pump pulse. These time constants are an order of magnitude faster than those seen in previous experiments in which the lone p-electron in was excited within the p-band. The results presented here imply that substantial relaxation of either electrons in the p-band or the hole in the s-band takes place prior to Auger emission, with electron–electron scattering playing a key role in the fast observed dynamics.     

Photoinduced multi-mode quantum dynamics of pyrrole at the – conical intersections

The photoinduced dynamics of pyrrole at the – S₀ and – S₀ conical intersections has been investigated by multi-mode time-dependent quantum wave-packet calculations. Diabatic potential-energy surfaces have been constructed for both conical intersection using accurate multi-reference ab initio electronic-structure calculations. In addition to the NH stretching coordinate, the three (four) symmetry-allowed coupling modes of A₂ (B₁) symmetry have been considered for the – S₀ (– S₀) conical intersections. Wave-packet dynamics calculations have been performed for three-dimensional models, taking account of the two dominant coupling modes of each conical intersection. The electronic population-transfer processes at the conical intersections, the branching ratio for the dissociation to the ground and excited states of the pyrrolyl radical, and their dependence on the initial preparation of the system have been investigated. It is shown that the excitation of the NH stretching mode strongly enhances the photodissociation rate, while the excitation of the strongest coupling mode has a pronounced effect on the branching ratio of the photodissociation process. Although the inclusion of the second (weaker) coupling mode has little effect on the electronic population dynamics, it leads to interesting changes of the nodal pattern of the wave packet at the conical intersections. The calculations provide insight into the effect of the multiple coupling modes on the process of direct photodissociation through a conical intersection.     

The role of water and K ion in the charge transfer between groups of DNA and the lysine and arginine side chains of histone proteins

We have calculated the charge transfer (CT) between the group of DNA and the lysine (Lys) and arginine (Arg) positive side chains of histones in presence of water and K⁺ ions. The calculations were performed at the HF + MP2 level, using the TZVP basis set. The calculations were corrected for basis set superposition error and besides Mulliken’s population analysis we have introduced the – for charged systems more reliable – natural population analysis. The results show that the bare -Lys and the -Arg interactions become weaker, mainly, due to the presence of the K⁺ ion. We have found 0.067e CT for Lys and 0.050e for Arg.     

Electroreduction of anions on chemically etched and electrochemically polished Bi(1 1 1) electrode

Electroreduction kinetics of to anions at chemically etched (CHE) and electrochemically polished (EP) Bi(1 1 1) electrodes has been studied using rotating disc electrode method. The surface nanostructure of CHE Bi(1 1 1) and EP Bi(1 1 1) electrodes has been studied by in situ STM and the very different values of root mean squared roughness (Rms) have been obtained (1000 times higher for CHE Bi(1 1 1) (Rms  143 nm) than for EP Bi(1 1 1) (Rms  0.145 nm)). The influence of the nanoroughness of CHE Bi(1 1 1) on the current density, heterogeneous reaction rate constant and corrected Tafel plots (cTp) has been demonstrated. For CHE Bi(1 1 1) the more pronounced inhibition of electroreduction reaction at moderate negative surface charge density has been observed in comparison with EP Bi(1 1 1), caused by the differences in surface charge density and also in diffuse layer ψ₀ potential drop values at crystallographically different homogeneous regions (planes) exposed at the surface of the macroheterogeneous polycrystalline CHE Bi(1 1 1) surface. The very low apparent transfer coefficient α_app obtained indicates the nearly activationless charge transfer mechanism for electroreduction at the CHE Bi(1 1 1) electrode similarly to EP Bi(1 1 1). However, α_app only very weakly depends on Rms for the Bi electrodes at high negative surface charge densities where the values of ψ₀ potential are nearly equal for different planes at fixed electrode potential. At very high negative surface charge densities the cationic catalysis through the adsorbed ion pairs is possible.     

Scavenging of and OH radicals in concentrated HCl and NaCl aqueous solutions

In neutral and acidic aqueous solutions containing 2 mol L⁻¹ of Cl⁻, the decay of the solvated electron and the formation of ClOH⁻ and were studied by picosecond pulse radiolysis experiment. The rate constant for the reaction of and H₃O⁺ is 1.3 × 10¹⁰ L mol⁻¹ s⁻¹. The yield of the OH radical at 100 ps is estimated to be 5.0 × 10⁻⁷  mol  J⁻¹.     

Geometries, stability and aromaticity of , [M(Al2P2)] (M = Li, Na, K, Cu) and N(Al2P2) (N = Be, Mg, Ca, Zn) clusters

Geometrical structure, aromaticity and other properties of , [M(Al₂P₂)]⁻ (M = Li, Na, K, Cu) and N(Al₂P₂) (N = Be, Mg, Ca, Zn) species are theoretically investigated with density functional theory (DFT) methods. Calculation results show that for species, the planar structure, with D_2h symmetry at the ¹A_g state, is the global minimum at the B3LYP/6-311+G_* level. Natural bond orbital (NBO) analysis indicates the existence of delocalization in the most stable species and its pyramidal complexes. Nucleus-independent chemical shift (NICS) and molecular orbital (MO) analysis further reveal that that pyramidal [M(Al₂P₂)]⁻ and N(Al₂P₂) species preserve the aromatic nature of the most stable unit.     

Transitions between P21, , and P6322 modifications of SrAl2O4 by in situ high-temperature X-ray and neutron diffraction

The results of in situ high-temperature X-ray and neutron powder diffraction experiments reconcile inconsistencies in previous reports on the symmetry of high-temperature phases of SrAl₂O₄. The material undergoes two reversible phase transitions and at 680 and 860 °C, respectively, and the latter one is experimentally observed and characterized for the first time. The higher symmetry above the transition is gained by disordering off-center split site of oxygen atoms around trigonal axis rather than by unbending Al–O–Al angle to the ideal value 180°. The analysis of the literature suggests that it is a common feature of the P6₃22 phases of stuffed tridymites.     

A DFT study of the hydration of monophosphate complexes of iron (III),

A systematic theoretical DFT study of the bonding between the cation Fe³⁺ and the anion was carried out. The role of water ligands is presented. Several isomers with tetrahedral, bipyramidal and octahedral environments around the iron ion were investigated. 5-fold coordination of the Fe³⁺ cation is found when 5 and 6 water molecules are included. Calculated infrared spectra are also presented.     

Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): and

Two new μ₃-oxo-centered trinuclear manganese complexes, one of them a homo-valence (1) pivalate complex and the other a mixed-valence (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are μ₃-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn₃O(Piv)₆(Im)₃]⁺ and outersphere pivalate ions, whereas in compound 2 interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.     

Solution thermodynamics near the liquid–liquid critical point. II. Excess second-order derivatives

We present a comprehensive study of the behaviour of excess second-order derivatives of binary mixtures near the liquid–liquid critical point. Specifically, excess (isobaric and isochoric) molar heat capacities ( and ), excess (isothermal and isentropic) compressibilities ( and ), and excess isobaric thermal expansivities () have been determined over the whole composition (x) range at atmospheric pressure and in the homogeneous region within (293.15–323.15) K. Results are consistent with the predictions of the current theory of critical phenomena. Remarkably, anomalous and curves in the critical region are observed. Such anomalies, which are reported here for the first time, are of significant size for and very mild in the case of , thereby indicating that volumetric effects at near-liquid–liquid criticality are, as expected, very small.     

Proton and protonic entities in solid heteropoly compounds: An ab initio calculation of the environmental effect on the ion

Systematic experimental investigations of heteropoly compounds, particularly their structure and activity, led to the conclusion that most of their characteristics are governed by the presence of protons and protonic entities. Special attention has been paid to two forms of 12-tungstophosphoric acid: hexahydrate (WPA-6) and dehydrated phase (WPA-0). It was postulated that in WPA-6 dynamic equilibrium of protonic entities exists, and that dehydrated phase is stabilized by protons. To confirm the role of the “free protons” or “proton gas” derived on the basis of thermal, structural and spectroscopic experimental studies, we carried out also ab initio calculations on a number of systems containing ion. We were not able to perform direct calculations on the real systems investigated experimentally since the structure of heteropoly compounds is too complex. However, it has been found that ion in WPA-6 definitely is not planar and the results obtained indirectly support the postulated dynamic equilibrium, i.e. possibility of existing of free protons.     

Partial charge ordering in the mixed-valent compound

Crystals of the mixed-valent compound were grown from a flux. The room temperature conductivity of a crystal was 3 S/cm but decreased smoothly with decreasing temperature to 10⁻⁵ S/cm at 25 K. Magnetic susceptibility data indicate a localized moment for Rh⁴⁺. A Seebeck coefficient at 200 K of +280 μV/K further confirms that this compound is a semiconductor rather than a metal with a partially filled 4d t_2g band. A structure refinement based on single crystal X-ray diffraction data obtained at 173 and 296 K provided Rh–O distances sufficiently accurate to indicate the nature of the charge ordering between Rh³⁺ and Rh⁴⁺. The large Seebeck coefficient coupled with the high electrical conductivity indicates that this may be a promising low-temperature thermoelectric material.