Specific fragmentation of [(CH3)2CO]Arn heteroclusters induced by the Ar L23- and O K-shell excitation

Ionic fragmentation following the inner-shell photoexcitation of [(CH₃)₂CO]Ar_n heteroclusters was investigated in the Ar L₂₃- and O K-edge regions. A partial ion yield (PIY) measurement revealed that and various acetone fragments (, , , , and CH_mCO⁺) were produced following the Ar L₂₃-shell excitation. In the O K-edge region, the PIY of O⁺ exhibited a sharp resonance peak at the O 1s → π^*(CO) resonance excitation. The selective O⁺ formation was interpreted as the suppression of statistical fragmentation, which was dominant in isolated acetone, owing to the dissipation of excess energy into Ar clusters.     

Photoelectron spectroscopic study of iron–benzene cluster anions

Iron–benzene cluster anions, (n = 1–7, m = 1–4), were generated via laser vaporization and studied using mass spectrometry, anion photoelectron spectroscopy and in one case by density functional theory. Based on these studies, we propose that and Fe₁Bz₁ as well as and Fe₂Bz₁ exhibit half-sandwich structures, that and Fe₁Bz₂, and Fe₂Bz₂, as well as Fe₃Bz₂ and Fe₄Bz₂ are sandwich structures, and that and Fe₂Bz₃ and larger species form ‘rice-ball’ structures which in each case consist of benzene molecules surrounding an iron cluster core.     

Nucleophilic and electrophilic radical attack on maleic and fumaric acids in aqueous solution

Rate coefficients (k) of CH₂OH, , and radical addition to maleic and fumaric acids were investigated between pH 1 and 8. Strong pH dependences observed were attributed to changes in protonation states of acids: H₂X, HX⁻ and X²⁻. k of CH₂OH, , addition to fumaric acid decreased in the order k_H2F>k_HF^->k_F^2- in agreement with the nucleophilic character of reaction. The electrophilic radical showed opposite tendency. With maleic acid the monoanion had the highest reactivity towards nucleophilic and the lowest one towards electrophilic radicals. This is attributed to a prevalence of steric over polar effects for HM⁻.     

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.     

Intense laser-induced decomposition of mass-selected 2-, 3-, and 4-methylaniline cations

Photodecomposition processes of 2-, 3-, and 4-methylaniline cations induced by a moderately intense (10¹¹ W/cm²) visible nanosecond laser field and an intense (10¹⁵ W/cm²) UV femtosecond laser field have been investigated using a tandem mass spectrometer. Highly unsaturated fragment cations such as and are dominantly produced by the nanosecond laser, while less unsaturated smaller fragment cations such as , and are produced mainly by the femtosecond laser. Ab initio calculations have also been performed to estimate the stable geometrical structures of and and those of possible intermediate ring compounds for discussing the photodecomposition pathways in intense laser fields.     

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.     

Effect of pressure and temperature on structural stability of potential hydrogen storage compound Li3AlH6

The crystal structure of Li₃AlH₆ was investigated at high pressures upto 27 GPa using a diamond anvil cell with synchrotron radiation in addition to high temperature X-ray diffraction. Density functional theoretical (DFT) calculations were performed simultaneously. While the structure of Li₃AlH₆ is stable on increasing temperature, the results of high pressure experiments show a pressure induced phase transition from the ambient phase to a high pressure cubic phase around 10.6 GPa. The transition pressure of 10.6 GPa and the bulk modulus value B₀ = 32(2) GPa for the phase obtained are in good agreement with the theoretical results.     

Is Cd2 truly a van der Waals molecule? Analysis of rotational profiles recorded at the , transitions

Rotational profiles of the ²²⁸Cd₂ isotopomer recorded in the (υ′, υ″) = (26, 0), (27, 0), (42, 0), (45, 0), (46, 0), (48, 0) vibrational bands of the transition were analysed. As a result, the , , , , and excited- as well as the ground-state rotational constants of the (¹¹⁴Cd)₂ were determined. The analysis allowed determining the absolute values for the and excited- and ground-state bond lengths, respectively. The obtained result – the – distinctly shorter than that obtained with assumption of pure ground-state van der Waals bonding, supports a theoretical prediction of a covalent admixture to the bonding. Analysis of the partially-resolved rotational profile recorded in the (υ′, υ″) = (38, 0) band of the same isotopomer recorded at the transition allowed estimating the rotational constant in the B1_u state.     

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.     

Franck–Condon simulation of photoelectron spectroscopy of HOO: Including Duschinsky effects

Geometry optimization and harmonic vibrational frequency calculations were performed on the and states of HOO and state of HOO⁻. The electron affinity and the term energy () of HOO were calculated at various theory levels. Franck–Condon analyses and spectral simulations were carried out on the and photodetachment processes. The spectral simulations of vibrational structures based on the computed Franck–Condon factors are in excellent agreement with the observed spectra. In addition, the equilibrium geometrical parameters of the state of HOO⁻ and state of HOO were obtained in the spectral simulations.     

Free-energy change of inserting halothane into different depths of a hydrated DMPC bilayer

Using the method of energy representation, we have calculated the free-energy change of inserting a halothane molecule into different depths of a hydrated dimyristoylphosphatidylcholine (DMPC) bilayer at pressures of to . Our results show that the free-energy change is more negative within the membrane than in bulk water. The halothane distribution is diffuse, and the preferred location is near the headgroup. The pressure effect is found to be minimal within the pressure range examined, which corresponds to previous biological experimental conditions.     

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.     

Adsorption of the first row of transition metals on the perfect and defective MgO(1 0 0) surface

We present DFT calculations for adsorption of the first row of transition metal atoms on a MgO(1 0 0) surface and on a surface exhibiting defects. Some atoms exhibit a high adsorption energy on the defect (e.g. Co, Ni and Cu), but others (Ca, Sc) rather adsorb on a clean surface and another set is indifferent to the presence of defect. The adsorption becomes energetically unfavorable when the σ anti-bonding orbitals become populated; this is worse on a defective surface than on a terrace. The π back-donation to the surface contributes to favor the adsorption on the center.     

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.     

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.     

Theoretical mapping of new L–(N)–L family of species with donor–acceptor bonding between N and ligand L

We perform a computational mapping study of a family of new inorganic species, based on idea of donor–acceptor type bonding between N⁺ and a ligand L with a terminal electron lone pair. The nitrogen ion is seen as being in an atomic ¹D state, with empty 2p acceptor orbitals [I.S.K. Kerkines., A. Papakondylis, A. Mavridis, J. Phys. Chem. A, 2002, 106, 4435]. We consider a series of small ligands, such as PN, CCH⁻, CCCN⁻, , and others. Chemical bonding analysis confirms the suggested bonding picture as characteristic for experimentally known and as well as for most of the predicted species. A number of these new compounds is found to be thermodynamically stable with respect to the existing or . They are candidates for new synthetic targets.     

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.     

Ab initio simulations of sulfuric acid solutions

Ab initio molecular dynamics simulations are presented for a solution consisting of a single H₂SO₄ molecule in a periodic box with 63 water molecules. Three trajectories lasting 35–55 ps were calculated at temperatures in the 320–326 K range, for two functionals, and double- and triple-zeta quality basis sets. All three trajectories displayed prompt ionization of the first proton. The ion displayed varying extents of ionization in the different trajectories. Proton hopping was observed between the oxygen atoms. Moreover, hopping of the solvating water molecules also occurred between the different oxygen atoms of the anions, with bidentate water, hydrogen bonding to two different oxygen atoms, serving as an intermediate.     

Excess thermodynamic properties, and for the binary systems {1,2-dichloropropane + 2-alkoxyethanols} at T = 298.15 K

This article presents the experimental data of and , obtained at T = 298.15 K and atmospheric pressure, for four binary systems composed of 1,2-dichloropropane (1,2-DCP) and four 2-alkoxyethanols. The 2-alkoxyethanols are 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), 2-propoxyethanol (2-PE) and 2-butoxyethanol (2-BE). The of the mixture has been shown positive for 2-ME, ‘s-shaped’ for all remaining systems, being negative at low and positive at high mole fraction of 1,2-DCP. The values for all binary mixtures are also shown both positive at low and negative at high mole fraction of 1,2-DCP. The experimental results of and were fitted to Redlich–Kister equation to correlate the composition dependence of both excess properties. In this work, data were also used to test the suitability of thermodynamic models (Wilson, NRTL, and UNIQUAC equations) based on local-composition theory. The results have been qualitatively discussed in terms of the polarity, self-association, and hydrogen bond among molecules.