Chemical Physics Letters (v.506, #1-3)

Contents (iii-viii).

The unique bonding characteristics of beryllium and the Group IIA metals by Michael C. Heaven; Vladimir E. Bondybey; Jeremy M. Merritt; Alexey L. Kaledin (1-14).
Display Omitted► Closed-shell Group IIA elements bond through hybridization and exchange interactions. ► Bonding trends vary erratically within Group IIA and the properties of beryllium are unique. ► The bonding for beryllium and Group IIA elements is challenging for quantum chemistry calculations. ► Spectra and calculations for beryllium compounds provide insights concerning the bonding.Having closed valence sub-shells, the alkaline earth atoms participate in covalent bonding via orbital hybridization and exchange interactions, with additional contributions from dispersion interactions. Starting from a closed ns 2 configuration imparts different characteristics to the chemistry of this group, as compared to metals that have open-shell atomic ground states. Theoretical studies of the bonding of the Group IIA metals have been pursued for many years, and they are known to be challenging for ab initio electronic structure methods. The bonding motifs have been examined, and the differences between beryllium and the remainder of the group explored. Experimental studies that probe the bonding, particularly for beryllium, have lagged behind the theoretical work. In the present Letter we describe our recent spectroscopic and theoretical investigations of simple beryllium compounds, and discuss these results in terms of their relationship to the properties of the heavier Group IIA elements.

Display Omitted► Iodine nitrite I–O–N=O has protocovalent O–N bond. ► Description of electronic structure of cis-IONO is more challenging that for its trans isomer. ► Amount of the electron density in the I–O and O–N bonds is less than 1.2e. ► Population of the I–O bond is 0.67e (cis) and 0.64e (trans).The geometrical and electronic structure of iodine nitrite, I–O–N=O, have been studied using DFT/B3LYP, MP2 and CCSD(T) methods. Topological analysis of the Electron Localization Function (ELF) performed at CCSD/TZVPP//CCSD(T)/TZVPP level reveals slightly polarized covalent N=O bond, the protocovalent N–O bond and mixed covalent–ionic I–O bond. The protocovalent N–O bond is described by two monosynaptic non-bonding basins, V(N) and V(O), with total basin populations of 1.1e in cis-IONO and 0.80e in trans-IONO, thus belonging to the charge-shift type. The I–O1 bond is essentially depleted with only 0.67e (cis) and 0.64e (trans).

Double ionization energies of HCl, HBr, Cl2 and Br2 molecules: An MRCI study by Lívia Streit; Francisco B.C. Machado; Rogério Custodio (22-25).
Display Omitted► Double ionization energies for HCl, HBr, Cl2 and Br2 are calculated using CASSCF/MRCI. ► Agreement with experimental data is achieved with absolute average deviations lower than 0.3 eV. ► Some double ionization energies not previously assigned are discussed.Accurate double ionization energies (DIEs) for low-lying doubly charged states of HCl, HBr, Cl2 and Br2 were calculated using non-relativistic CASSCF/MRCI level of theory with the aug-cc-pVQZ basis set. The results are in excellent agreement with experimental data, presenting absolute average deviations lower than 0.3 eV. Some DIEs not previously assigned or well characterized are discussed. Further improvements can be reached by including relativistic effects.

Active control scheme and mechanism in the two-pulse molecular alignment by Shitong Zhao; Hui Lu; Peng Liu; Ruxin Li; Zhizhan Xu (26-30).
Display Omitted► Provide an analytical and numerical analysis of two – pulse molecular alignment. ► Propose the transition probability back to original states to evaluate the control mechanism. ► Molecular rotational wavepacket is actively controlled by the bi-pulse delay.The maximal field-free molecular alignment achievable by two ultrafast laser pulses can be actively controlled by predetermining the timing of the second pulse according to the molecular alignment by the first pulse. We demonstrate that the active control scheme is manifested by the probability of Raman transition back to the original states. When the time delay between two aligning pulses varies, constructive or destructive interference occurs among different quantum paths, leading to the modulation of the transition probability back to the initial rotational states, therefore can control the molecular alignment and also the contribution from even/odd states.

Resonant two-photon detachment of WO2 by Jennifer E. Mann; Sarah E. Waller; David W. Rothgeb; Caroline Chick Jarrold (31-36).
Display Omitted► The R2PD spectrum of WO2 anion in the 1.75–2.41 eV range is reported. ► Two distinct electronic bands are observed and assigned to valence-bound states. ► The spectrum is compared to the 3.493 eV photoelectron spectrum of WO2 anion. ► One of the bands exhibits doublets attributed to spin–orbit splitting.The resonant two-photon detachment spectrum of WO2 in the 1.75–2.41 eV range exhibits at least two electronic transitions near the detachment continuum of WO2 . The states are assigned to valence-bound states of the anion, rather than dipole bound states, in part because the observed bending frequencies are considerably lower than those in the neutral. One band exhibits doublets, which is attributed to spin–orbit splitting in the two E1/2 sub-states of a quartet anion state. A qualitative assignment of the spectrum is made based on comparison with the photoelectron spectrum of WO2 , as well as density functional theory calculations.

Positron annihilation studies in solid substituted aromatic compounds by F.C. Oliveira; A.M. Oliveira; C.L. Donnici; J.C. Machado; W.F. Magalhães; D. Windmöller; F.H. Fulgêncio; L.R. Souza (37-41).
Display Omitted► Aromatics with electron donating groups increase positronium formation probability. ► Ratio of positronium formation probability are used in a modified Hammett equation. ► Positronium formation are more intense in meta substituent groups.Positronium formation was investigated in benzene and naphthalene compounds with electron donating (―NH2 and ―OH) and electron withdrawing (―CN and ―NO2) substituents. The results exhibit an increase in the positronium formation yield whenever donating groups are bound to the ring and a decrease with withdrawing groups. These results can be attributed to the π-system electronic density variation in the aromatic ring. The amount of positronium obtained, I 3 parameter, has been correlated with the Hammett (σ) and Brown–Okamoto ( σ p + ) constants and adjusted through the modified Hammett equation, which employs the ratio I 3 / I 3 ϕ , yielding a satisfactory fit.

Electronic hole localization in rutile and anatase TiO2 – Self-interaction correction in Δ-SCF DFT by Paweł Zawadzki; Karsten Wedel Jacobsen; Jan Rossmeisl (42-45).
Display Omitted►Lattice distortion leads to an electronic hole localization in titanium dioxide. ► We correct for the delocalization error in semi-local Density Functional Theory. ► Self-trapped (localized) hole in anatase is more stable than in rutile.We study electronic hole localization in rutile and anatase titanium dioxide by means of Δ-Self-Consistent Field Density Functional Theory. In order to compare stabilities of the localized and the delocalized hole states we introduce a simple correction to the wrong description of the localization processes within DFT. The correction removes the non-linearity of energy for fractional excitations. We show that the self-trapped and the delocalized hole states have comparable stability in rutile TiO2 whereas in anatase the former is favoured. The theoretical prediction of the adiabatic Potential Energy Surfaces for the hole localization compares well with published photoluminescence measurements.

Display Omitted► Photoisomerization rates and rotational mobility of spin-labeled azobenzenes in polymer glass. ► Quasi-libration amplitudes correlate with quantum yields of trans–cis isomerization. ► Reaction extent is determined by the fraction of molecules with sufficient mobility.The rate of photochemical isomerization of azobenzene derivatives dispersed in glassy polystyrene has been measured along with rotational mobility of reacting molecules. For this purpose bifunctional probe molecules carrying a paramagnetic nitroxide fragment and a photochromic azobenzene moiety were used. The kinetics of photoisomerization was followed by monitoring the change in the UV–Vis absorbance spectra. Rotational mobility was determined by numerical simulation of the ESR spectra. It has been shown that in the matrix of glassy polystyrene amplitudes of high-frequency angular displacements (quasi-librations) correlate with the rate of photochemical trans–cis isomerization.

Display Omitted► C60O1-3 and C70O polarizabilities do not depend on structure and are determined by the O atoms number. ► The polarizability of C60О n epoxides achieves maximal value at n  = 15 and then diminishes. ► The depression of polarizability is caused by the pressure of O atoms on the C60 framework.At the first time eigenvalues of polarizability tensors, average polarizabilities and their anisotropies of epoxyfullerenes C60O n , C70O (n  = 1–30) and oxahomofullerenes C60O, C70O have been calculated. The dependences of C60О n and С70О polarizabilities on the structure and n values have been discovered and general approaches for design of fullerene oxy-derivatives with high polarizability are discussed. The polarizability of C60О n epoxides achieves maximal value 87.4 Å3 at n  = 15 and then diminishes to 85.3 Å3 for n  = 30. A theoretical model of this phenomenon has been proposed.

Display Omitted► A facile method for turning the packing density of gold nanoparticles (GNPs) over glass substrates. ► The degree of GNP aggregation was increased with rising chain length of diamines. ► C-8 diamines produced the homogeneous 2-dimensional array of GNPs over glass substrates.Bi-functional diamines with different chain lengths were investigated to control the packing density of large gold nanoparticles (ca. 60–80 nm) over glass substrates. Diamine linkers induced the lateral immobilization of neighboring gold nanoparticles (GNPs) on the amine-functionalized glass surface. The molecular bridging force of diamines was proportional to the number of CH2 groups: 1,4-diaminobutane (C-4) < 1,8-diaminooctane (C-8) < 1,12-diaminododecane (C-12). Even though the aggregation of Au colloids was more sensitive to C-12 diamines, the uniform and densely-packed array of GNPs over glass substrates were accomplished by the addition of C-8 diamines possessing optimal chain length with a balanced binding force on Au colloids.

Nonlinear absorption and photoluminescence emission in nanocomposite films of Fuchsine Basic dye–polymer system by G. Sreekumar; P.G. Louie Frobel; S. Sreeja; S.R. Suresh; S. Mayadevi; C.I. Muneera; C.S. Suchand Sandeep; Reji Philip; Chandrachur Mukharjee (61-65).
Display Omitted►Organic-polymer nanocomposite films of excellent surface smoothness were fabricated. ► In the Z-scan experiment, a switchover from SA to TPA occurred near the focus. ► The organic-polymer nanocomposite films displayed intense PL emission at room temperature.Fuchsine Basic dye–polyvinyl alcohol composite films were fabricated and their structure, nonlinear absorption as well as linear absorption and photoluminescence properties were investigated. Switchover from saturable absorption to two-photon assisted excited state absorption with increase in intensity was observed in the open aperture Z-scan study (Nd:YAG, 532 nm, 7 ns). The effective two-photon absorption coefficient β was found to be several orders higher than that reported for rhodamine B. The dye–polymer films were characterized as nanocomposites with dye microdomains encapsulated between molecules of the amorphous polymer and having average surface roughness as low as ≈0.46 nm. The samples also exhibited intense photoluminescence emission when excited with 534 nm radiation.

Study of the structural organization of cyclodextrin–DNA complex loaded anionic and pH-sensitive liposomes by Sônia M.L. Silva; Letícia N. Coelho; Ângelo Malachias; Carlos A. Perez; Jorge L. Pesquero; Rogério Magalhães-Paniago; Mônica C. de Oliveira (66-70).
Display Omitted► Cyclodextrin/DNA complex leads to formation of lamellar and hexagonal phases of DOPE. ► Cyclodextrin/DNA complex did not avoid lamellar-hexagonal phase transition of DOPE. ► Cyclodextrin/DNA complex loaded liposomes is less ordered in biological medium. ► pH-sensitivity of cyclodextrin/DNA complex loaded liposomes is maintained.The present study investigated the effect of the 6-monodeoxy-6-monoamine-β-cyclodextrin(Am-β-CD)/DNA (Am-β-CD/DNA) complex, as well as of culture medium components and proteins, at pH 7.4 and 5.0, on membranes of anionic and pH-sensitive liposomes comprised of DOPE–CHEMS, using energy dispersive X-ray diffraction (EDXD). At pH 7.4, the Am-β-CD/DNA complex induced the appearance of lamellar and hexagonal phases of DOPE. However, at pH 5.0, only non-lamellar phases could be observed. The presence of biological components led to a disruption of lipid order, but the pH-sensitivity of liposomes was maintained.

Free volume of poly(perfluorosulfonic acid)/SiO2 composite proton exchange membranes by 129Xe NMR by Lavinia Utiu; Carmen Filipoi; Dan E. Demco; Xiaomin Zhu; Rostislav Vinokur; Oliver Conradi; Andreas Graichen; Bernhard Blümich; Martin Möller (71-75).
Display Omitted► This work provides the first investigation of free volume in composite PEM by 129Xe NMR spectroscopy and relaxometry. ► The free volume in PFSA/SiO2 membranes shows a maximum at 2 wt.% content in silica. ► The free volume is heterogeneous.Poly(perfluorosulfonic acid)/silica (PFSA/SiO2) composites were investigated by 129Xe NMR spectroscopy and relaxometry. 129Xe chemical shift extrapolated to zero pressure was used for calculation of average free volume hole size. This quantity reaches a maximum at 2 wt.% SiO2 that could be correlated to the performance of composites proton exchange membrane. 129Xe longitudinal magnetization relaxation revealed a bimodal distribution of the free volume that was explained by the presence of xenon atoms in the backbone and pendant–chain domains. Thus, the free volume is heterogeneous and depends on the content of SiO2. Implications of the free volume changes for the hydrogen crossover through PFSA/SiO2 membranes are also discussed.

Versatile protein-based bifunctional nano-systems (encapsulation and directed assembly): Selective nanoscale positioning of gold nanoparticle-viral protein hybrids by Bin Zheng; Nobuyuki Zettsu; Megumi Fukuta; Mutsunori Uenuma; Tatsuya Hashimoto; Kentaro Gamo; Yukiharu Uraoka; Ichiro Yamashita; Heiji Watanabe (76-80).
Display Omitted► We managed to encapsulate gold nanoparticles using recombinant bifunctional protein. ► We managed to position protein-encapsulated gold nanoparticles on desired substrate. ► We managed to position one single gold nanoparticle on desired nano-site.We demonstrate a selective nanoscale positioning of targeted Au nanoparticles (NPs) through a bifunctional protein-based encapsulation/delivery system. The newly designed recombinant bifunctional protein, appended with both gold-binding peptide (GBP) and Ti/Si-binding peptide (TBP) at the C- and N-termini efficiently encapsulated 15–20 nm-diameter Au NPs during the pH-controlled reversible reassembly process, and showed the ability of the internalized Au NPs in selective binding to nanometer-scale Ti islands without overshooting. This highly controlled placement of the Au NPs on substrates can be employed to make both large scale devices and point-contact devices.

Filtering carbon dioxide through carbon nanotubes by Dimitrios Mantzalis; Nikolaos Asproulis; Dimitris Drikakis (81-85).
Display Omitted► This work study the layering formation around SWCNT through MD. ► The formation of primary, secondary and even tertiary layers is observed. ► The formation of the additional layers is dependent on tube’s size and gas-structure interactions. ► Low pressures primarily affect the adsorption undergone by the external surface of the CNTs.Layering phenomena of carbon dioxide transported through carbon nanotubes are investigated through molecular dynamics simulations. The layering formation is examined for carbon nanotubes spanning from (8, 8) to (20, 20) subjected to pressures and temperatures that range from 1 to 20 bar and 300 to 400 K, respectively. Well defined layers are developed around the internal and external surface of the nanotubes for all the examined cases. It is shown that the number of layers along with their relative strength varies as a function of the nanotube’s diameter, size, carbon dioxide density and gas-structure interactions.

Fullerene-like CS x : A first-principles study of synthetic growth by C. Goyenola; G.K. Gueorguiev; S. Stafström; L. Hultman (86-91).
Display Omitted► Synthetic growth of Fullerene-Like Sulpho Carbide (FL-CS x ) was studied by DFT. ► Precursors with impact for CS x are the neutrals SCCS, SCS, CCS, C 2 S 4, and the anions CCS, C 2 S, C 2. ► Similar to other FL-compounds, defects in CS x include pentagons. ► Structuraly, FL-CS x is between FL-Carbon Nitride and FL-Phosphorus Carbide.Fullerene-Like (FL) Sulpho-Carbide (CS x ) compounds have been addressed by first principles calculations. Geometry optimization and cohesive energy results are presented for the relative stability of precursor species such as C2S, CS 2, and C 2 S 2 in isolated form. The energy cost for structural defects, arising from the substitution of C by S is also reported. Similar to previously synthesized FL-CN x and FL-CP x compounds, the pentagon, the double pentagon defects as well as the Stone–Wales defects are confirmed as energetically feasible in CS x compounds.

Display Omitted► CH x and CH x O species adsorbed on various sites of a Pd79 nanoparticle are studied. ► For that, density-functional calculations are performed. ► The structures, energies and vibrations of the adsorption complexes are considered. ► Low coordinated sites can bind by up to 20–50 kJ/mol stronger than the terrace sites. ► Spectroscopic detection of the adsorbates on terrace and edge Pd sites is addressed.This computational study deals with the adsorption of CH3, CH2, CH, CH2OH, CH3O, CH2O and CHO species on a nanoparticle Pd79 that mimics experimentally investigated model Pd catalysts. We quantify structural, energetic and vibrational parameters of these adsorption complexes and analyse their dependence on the adsorption site. Most of the considered low coordinated adsorption sites are found to be favoured by 20–50 kJ/mol over the sites on (1 1 1) facets. Some of the studied species have distinguishable vibrational parameters at different adsorption sites of the model nanoparticle, making possible spectroscopic characterization of respective adsorption complexes.

Labile electronic and spin states of the CaMn4O5 cluster in the PSII system refined to the 1.9 Å X-ray resolution. UB3LYP computational results by Keita Kanda; Shusuke Yamanaka; Tohru Saito; Yasufumi Umena; Keisuke Kawakami; Jian-Ren Shen; Nobuo Kamiya; Mitsutaka Okumura; Haruki Nakamura; Kizashi Yamaguchi (98-103).
Display Omitted► A first ab initio study of the manganese cluster with the 1.9 Å X-ray resolution. ► We examined all possible axial spin structures using B3LYP method of Mn(IV)4 and Mn(III)4 cases. ► We analyzed the energy spectra of spin states using Heisenberg 6 J model. ► Energy gaps are quite small, which is related to the labile character of the cluster.UB3LYP calculations were first performed to elucidate electronic and spin structures of the CaMn4O5 cluster in the oxygen-evolving-complex of the PSII system refined to the 1.9 Å X-ray resolution by Kamiya, Shen, and their collaborators. Eight different UB3LYP solutions with axial spin structures were constructed to obtain the energy levels of the cluster on the basis of their X-ray structure. The energy diagrams were analyzed in terms of the Heisenberg model that involves six effective-exchange integrals between manganese ions. Several characteristic features of the electronic states of the cluster are revealed from these theoretical investigations based on the UB3LYP calculations.

Display Omitted►Non-restricted working equations of the dual descriptor have been proposed. ► Total electronic density and densities of frontier molecular orbitals were used as approaches. ► Degeneration in frontier molecular orbitals has been taken into account too. ► Restricted f NS(r) and f NN(r) Fukui functions have been integrated into one analytical generalized Fukui function.Two hierarchical working equations to calculate the dual descriptor for electronic open-shell systems were deduced based on the formalism of the Conceptual Spin-Polarized Density-Functional Theory (SP-DFT). NO and O2 molecules were analyzed by taking into account their ground state multiplicities. The NO molecule has been used as a typical conventional example of a system with a doublet multiplicity presenting non-degenerate frontier molecular orbitals and the O2 molecule has been considered as a typical example of a system with a triplet multiplicity presenting degenerate frontier molecular orbitals. One working equation was tested in carbenes.

Fragment molecular orbital calculations under periodic boundary condition by Takatoshi Fujita; Tatsuya Nakano; Shigenori Tanaka (112-116).
Display Omitted► The periodic boundary condition is incorporated in the fragment molecular orbital method. ► Benchmark calculations for (H2O)64 were carried out. ► The present method was applied to molecular dynamics simulation for liquid water. ► Calculated radial distribution functions are in reasonable agreement with experiments.The periodic boundary condition (PBC) is incorporated in the fragment molecular orbital (FMO) method to appropriately describe systems with aqueous solutions. We present benchmark calculations for ( H 2 O ) 64 and show that this PBC-FMO method can eliminate artificial surface effects. An application to molecular dynamics simulation for liquid water is also shown, and calculated radial distribution functions are in reasonable agreement with those obtained from experiments. It is thus confirmed that the present PBC-FMO method is useful for ab initio simulations in aqueous solution.

Display Omitted► Raman spectroscopy of single levitated water droplets in air at low temperature. ► Single supercooled aqueous solution droplets could be levitated stably in air. ► Snapshots of freezing event of aqueous solution droplets in air are reported.The freezing processes of single micrometer-sized aqueous ammonium sulfate droplets levitated in air were observed by means of laser trapping and spectroscopy techniques. Single micrometer-sized aqueous ammonium sulfate droplets were levitated by radiation pressure in air. When a levitated droplet was cooled below 213 K, a supercooled droplet was turned from the liquid to solid state. To the best of our knowledge, this is the first observation of the freezing processes of single micrometer-sized supercooled aqueous solution droplets in air by means of laser trapping and spectroscopy techniques.

Electronic ground state conformers of β-carotene and their role in ultrafast spectroscopy by Vladimír Lukeš; Niklas Christensson; Franz Milota; Harald F. Kauffmann; Jürgen Hauer (122-127).
Display Omitted► Calculation of potential energy curve for the rotation of one terminal group of β-carotene. ► The curve exhibits two closely spaced energetic minima. ► Upon excitation of the global minimum, the well know S1 state is formed. ► Excitation of the higher lying local minimum leads to population of the intensely debated S stateWe present a study of ground state conformations of all-trans β-carotene using Density Functional Theory (DFT). To reproduce the carotenoid spectrum, the DFT approach was combined with the Multi-Reference Configuration Interaction. Our results show that the global minimum corresponds to an asymmetric structure where the β-ionone rings are twisted with respect to the polyene chain. The next higher-lying conformer is more s-cis symmetric and is populated at room temperature (30%). We discuss the relation of these conformers to S and show that our model readily explains the temperature dependence and the narrowing of the ground state bleach at long population times.