Spectral properties of Er3+/Yb3+ codoped tungsten-tellurite glasses

The spectral properties of Er3+/Yb3+ codoped tungsten-tellurite (WT) glasses have been investigated. The measured absorption spectra are analyzed by Judd-Ofelt theory. The compositional change of intensity parameter omega2 is attributed to the change in the covalency between the Er3+ and oxygen ions, the asymmetry in the local structures around the Er3+ ions can be neglected. The lifetimes of 4I(13/2) level of Er3+ in WT glasses are measured and comparable with other TeO2-based glasses. The stimulated emission cross-section is calculated based on McCumber theory. The fluorescence full width at half maximum (FWHM) and the emission cross-section (sigma(peak)) of the 4I(13/2) --> 4I(15/2) transition of Er3+ in different glass hosts have been compared. The suitability of such WT glasses as host materials for 1.5 microm broadband amplification is discussed.     

Pulse Duration Dependent Asymmetry in Molecular Transmembrane Transport Due to Electroporation in H9c2 Rat Cardiac Myoblast Cells In Vitro

Electroporation (EP) is one of the successful physical methods for intracellular drug delivery, which temporarily permeabilizes plasma membrane by exposing cells to electric pulses. Orientation of cells in electric field is important for electroporation and, consequently, for transport of molecules through permeabilized plasma membrane. Uptake of molecules after electroporation are the greatest at poles of cells facing electrodes and is often asymmetrical. However, asymmetry reported was inconsistent and inconclusive—in different reports it was either preferentially anodal or cathodal. We investigated the asymmetry of polar uptake of calcium ions after electroporation with electric pulses of different durations, as the orientation of elongated cells affects electroporation to a different extent when using electric pulses of different durations in the range of 100 ns to 100 µs. The results show that with 1, 10, and 100 µs pulses, the uptake of calcium ions is greater at the pole closer to the cathode than at the pole closer to the anode. With shorter 100 ns pulses, the asymmetry is not observed. A different extent of electroporation at different parts of elongated cells, such as muscle or cardiac cells, may have an impact on electroporation-based treatments such as drug delivery, pulse-field ablation, and gene electrotransfection.     

Steering dissociation of Br2 molecules with two femtosecond pulses via wave packet interference

The dissociation dynamics of Br2 molecules induced by two femtosecond pump pulses are studied based on the calculation of time-dependent quantum wave packet. Perpendicular transition from X 1Sigma g+ to A 3Pi 1u+ and 1Pi 1u+ and parallel transition from X 1Sigma g+ to B 3Pi 0u+, involving two product channels Br (2P3/2)+Br (2P3/2) and Br (2P3/2)+Br* (2P1/2), respectively, are taken into account. Two pump pulses create dissociating wave packets interfering with each other. By varying laser parameters, the interference of dissociating wave packets can be controlled, and the dissociation probabilities of Br2 molecules on the three excited states can be changed to different degrees. The branching ratio of Br*/(Br+Br*) is calculated as a function of pulse delay time and phase difference.     

Vibrational dynamics of excited electronic states of molecular iodine

Femtosecond degenerate four-wave-mixing spectroscopy following an initial pump laser pulse was used to observe the wave packet dynamics in excited electronic states of gas phase iodine. The focus of the investigation was on the ion pair states belonging to the first tier dissociating into the two ions I-(1S) + I+(3P2). By a proper choice of the wavelengths of the initial pump and degenerate four-wave-mixing pulses, we were able to observe the vibrational dynamics of the B (3)Pi(u) (+) state of molecular iodine as well as the ion pair states accessible from there by a one-photon transition. The method proves to be a valuable tool for exploring higher lying states that cannot be directly accessed from the ground state due to selection rule exclusion or unfavorable Franck-Condon overlap.     

Predissociation Dynamics of B State of Methyl Iodide with Femtosecond Pump-probe Technique

The predissociation dynamics of B Rydberg state of methyl iodide is studied with femtosecond two-color pump-probe time-of-°ight spectra at pump pulse of 400 nm and probe pulse of 800 nm. The dominant product channels are the CH3I+ and CH3+ formation. The time-dependent signals for CH3I+ and CH3+ ions are obtained. Both of the signal curves can be ˉtted by biexponential decays with time constants of ?1 and ?2, ?1 is assigned to the lifetimes of high Rydberg states, which can be accessed by absorbing three 400 nm pump pulses and ?2 re°ects the dynamics of B Rydberg state, which is accessed with two pump pulses. The lifetime of B Rydberg state is determined to be about 1.57 ps, which is incredibly consistent with the previous studies. The results were interpreted as a multiphoton dissociative ionization processes.     

Electron transfer from sodium to oriented nitromethane, CH3NO2: probing the spatial extent of unoccupied orbitals

Beams of sodium atoms with energies of a few eV are crossed with a beam of oriented CH3NO2 molecules to study the effect of collision energy and orientation on electron transfer. The electron transfer produces Na+ ions and free electrons, parent negative ions (CH)NO2-), and fragmentation ions NO2- and O- in proportions that depend on the collision energy. The steric asymmetry is very small or zero and suggests that production of all of the ions is favored by sideways attack with respect to the permanent dipole along the C-N axis. In these experiments, the electron appears to be transferred into the 2B1 state of the anion comprising mainly the pi*NO LUMO, producing a valence-bound state rather than a dipole-bound state.     

Evolution of ordered films of copper phthalocyanine according to EPR data

The procedure for calculating the orientation distribution of molecules using the angular dependence of EPR spectra was employed to study copper(II) phthalocyanine (CuPc) films varying in thickness and obtained by depositing the molecular complex on flat quartz plates. At the first stage of deposition, a layer of the α-CuPc phase with preferable orientation of molecular stacks along the plate surface is formed. At the second stage, a layer with an orthogonal arrangement of molecular stacks is condensed over the first layer. The interaction with NO₂ forms CuPc binuclear associates. Analysis of the EPR spectra made it possible to determine the symmetry of the structure and the distance between the paramagnetic Cu²⁺ ions; the structure of the associates has been proposed. The orientation distribution of CuPc dimers in the film depends both on the initial ordering in the film and on processing conditions. Strong disordering of molecular stacks in ordered films during the α-CuPc to α-CuPc phase transition has been found.     

563～660 nm波段SO2+的PHOFEX连续谱

在超声分子束条件下,利用380.85 nm的电离激光使SO2分子经由[3+1]共振增强多光子电离(REMPI)产生纯净的SO2+(X 2A1)分子离子,用另一束解离激光在可见光波长区(563～660 nm)扫描获得了光解碎片SO+的激发(PHOFEX)谱.从563～660 nm波长区SO+的无结构连续谱以及SO2+解离的效率随波长增加而减少的实验事实,提供了SO2+(E,D,C)电子态附近存在α2A2对称性排斥态的证据,分析了产生SO+的[1+1]光解机理:(1)SO2+(X2A1)首先经由单光子激发到达B2B2中间态的密集能级区;(2)吸收另一个光子到达SO2+(E,D,C)电子态附近的α2A2排斥态,经由α2A2排斥态产生了到SO+(X2∏)+O(3Pg)的直接解离.     

盐水溶液中离子与丙氨酸极性基团间的作用对丙氨酸缔合的影响:密度泛函理论与分子动力学模拟

采用密度泛函理论和经典分子动力学模拟研究了盐水溶液中Na⁺、Cu²⁺、Zn²⁺、Cl^-与丙氨酸分子间的相互作用对丙氨酸分子缔合的影响. 密度泛函理论的计算结果显示丙氨酸分子与Na⁺、Cu²⁺、Zn²⁺、Cl^-之间的相互作用可增强其电荷分离. 经典分子动力学模拟结果显示在水溶液中两性离子形式的丙氨酸存在三种缔合结构.盐水溶液中, 阳离子、阴离子与丙氨酸间的相互作用均能一定程度上减弱丙氨酸分子的缔合. 但是阳离子与丙氨酸间的相互作用明显受离子水合作用的影响. 由于Cu²⁺水合作用较强, 虽在气相中Cu²⁺与丙氨酸分子之间相互作用明显比Na⁺强, 但是在水溶液中则情况刚好相反. 在ZnCl₂稀溶液中, Zn²⁺与丙氨酸间的相互作用被其第一水合壳层隔开. 但这种相互作用仍能明显影响丙氨酸分子的缔合, 这与Zn²⁺的水合壳层特征有关. 另外, 离子与丙氨酸之间的相互作用, 不仅会削弱丙氨酸的缔合, 也可导致丙氨酸分子间的缔合结构发生转变. 离子浓度也会影响其与丙氨酸分子间的缔合形式以及丙氨酸的缔合结构.     

Comparative study of multielectron ionization of alkyl halides induced by picosecond laser irradiation

The interaction of C2H5X, 1-C3H7X, 1-C4H9X, where X = I, Br, Cl, with strong (1 x 10(13)-1.2 x 10(14) W/cm2) 35 ps laser pulses at 1064 nm is studied by means of time-of-flight mass spectrometry. The multielectron ionization following the C-X bond elongation has been verified for the studied molecules. By combination of the intensity dependence of the ion yields, the estimated kinetic energies of the released fragment ions, and their angular distributions, we have identified the different dissociation channels of the transient multiply charged parent ions. From the dependence on the laser intensity of the ratio of the doubly charged halogen ions to the singly charged ones, it is concluded that the molecular coupling with the laser field increases with the molecular size.     

Steric asymmetry in electron transfer from potassium atoms to oriented nitromethane (CH3NO2) molecules

Electrons are transferred in collisions between potassium atoms and CH(3)NO(2) molecules that have been oriented in space prior to collision. The electron transfer produces K(+) ions, parent negative ions CH(3)NO(2)(-), and the fragment ions e(-), NO(2)(-), and O(-) in amounts that depend on the energy. The positive and negative ions are detected in coincidence by separate time-of-flight mass spectrometers at various collision energies for both CH(3)-end attack and NO(2)-end attack. The steric asymmetry for electrons and CH(3)NO(2)(-) is essentially zero, but the steric asymmetry for NO(2)(-) shows that NO(2)(-) is formed mainly in CH(3)-end collisions. There is evidence that the electrons and NO(2)(-) have the same transient precursor, despite having different steric asymmetries. It appears likely that the precursor is formed by electron transfer mainly in collisions normal to the molecular axis leading to near zero steric asymmetry for the electron. This transient precursor can also eject an NO(2)(-) ion, which is more likely to be removed as KNO(2) salt when K(+) ions are near the NO(2) end of the molecule, with the result that CH(3)-end collisions seem to produce more NO(2)(-).     

Polarized laser-induced photofragmentation studies of JKM-selected CH3I molecules: retention of orientation in optical and DC electric fields

The technique of linearly polarized laser-induced photofragmentation for the measurement of the degree of orientation of rotationally state-selected symmetric top molecules [Phys. Rev. Lett.59, 2951 (1987)] has been used to study the retention of molecular orientation in optical frequency AC and homogeneous DC electric fields. For CH₃I beams, state-selected by the electrostatic hexapole focuser in several specific low-J parent states, recoupling of the iodine nuclear spin with the molecular rotational angular momentum occurs rapidly in weak fields, leading to some loss of orientation, but the resulting degree of orientation (i.e., theM _F distribution) is retained in both DC and optical frequency electric fields. The direction of the orientation of the molecular axis can be inverted with 100% efficiency by changing the sign of the DC ‘orienting field’. The up/down asymmetry of the photofragment angular distribution can be observed with either parallel (vertical) or perpendicular (horizontal) laser polarization.     

Coulomb explosion of nitrogen and oxygen molecules through non-Coulombic states

We have systematically studied Coulomb explosion of nitrogen and oxygen molecules in intense 8 and 24 fs laser pulses. In the experiment, we explicitly separated all explosion pathways through coincident measurements. The high resolution kinetic energy releases (KERs) and the exotic angular distributions of atomic ions provide direct evidence that Coulomb explosion occurs through non-Coulombic states. In the theory, we calculated dissociation potential energy curves (PECs) of nitrogen and oxygen molecules and their multicharged molecular ions using multiconfiguration second-order perturbation theory. The results indicate that Coulomb potentials are close to the accurate PECs of multicharged molecular ions only when the internuclear distance is larger than 3 ?. In comparison with the experimental observations and the theoretical calculations, we determined the internuclear distance when Coulombic explosion occurs. It is near the equilibrium distance of the neutral molecules in the case of 8 fs laser pulses and expands gradually with the increase of the charge state of the molecular ions in the case of 24 fs laser pulses.     

Competing ion decomposition channels in matrix-assisted laser desorption ionization

We gauged the internal energy transfer for two dissociative ion decomposition channels in matrix-assisted laser desorption ionization (MALDI) using the benzyltriphenylphosphonium (BTP) thermometer ion [PhCH 2PPh 3] (+). Common MALDI matrixes [alpha-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA), and 2,5-dihydroxycinnamic acid (DHB)] were studied with nitrogen laser (4 ns pulse length) and mode-locked 3 x omega Nd:YAG laser (22 ps pulse length) excitation. Despite the higher fluence required to initiate fragmentation, BTP ions indicated lower internal energy transfer with the picosecond laser in all three matrixes. These differences can be rationalized in terms of phase explosion induced by the nanosecond laser vs a stress-confinement-driven desorption mechanism for the picosecond laser. For the two ion production channels of the BTP thermometer ion, breaking a single bond can result in the formation of benzyl/tropylium ions, F1, or triphenylphosphine ions, F2. In SA and DHB, as well as in CHCA at low fluence levels, the efficiency of these channels (expressed by the branching ratio I F1/ I F2) is moderately in favor of producing tropylium ions, 1 < I F1/ I F2 < 6. As the laser fluence is increased, for CHCA, there is a dramatic shift in favor of the tropylium ion production, with I F1/ I F2 approximately 30 for the nanosecond and the picosecond laser, respectively. This change is correlated with the sudden increase in the BTP internal energies in CHCA in the same laser fluence range. The large changes observed in internal energy deposition for CHCA with laser fluence can account for its ability to induce fragmentation in peptides more readily than SA and DHB.     

Chloride attachment negative-ion mass spectra of sugars by combined liquid chromatography and atmospheric pressure chemical ionization mass spectrometry

A method has been developed for the rapid determination of sugars, including molecular weight measurements, using high-performance liquid chromatography coupled with negative-ion, atmospheric-pressure chemical-ionization mass spectrometry. The chromatography was carried out on a 250 x 4 mm I.D. column packed with 7 microns NH2-silica. The mobile phase consisted of a high percentage of methanol or acetonitrile with a small amount of chloroform. During the mass spectrometry, a strong base is formed from the polar solvent molecules by corona discharge, followed by ion-molecule reactions in the chemical ionization ion source (e.g. the methoxy anion is formed from methanol). This strong base reacts with the chloroform, generating chloride ions, which in turn react with the neutral sugar molecules as they elute from the chromatograph. The chloride ion and sugar interactions yield chloride-attachment ions, which are further stabilized by successive collisions. In this method, authentic monosaccharides and some oligosaccharides show dominant quasi-molecular ions, [M + Cl]-, with little fragmentation, and its particularly useful for the molecular weight determination of sugars.     

Interactions of N-acetyl-l-cysteine with metals (Ni2+, Cu2+ and Zn2+): an experimental and theoretical study

In recent years, interactions of metal ions with amino acid derivatives have been studied extensively due to their immense importance in the life-supporting processes. Here, we report the synthesis of three metal (Ni²⁺, Cu²⁺, and Zn²⁺) complexes of N-acetyl-l-cysteine (NAC) using a solvent-free solid-state method. Characterization of the complexes by elemental analyses, molar conductance, SEM, infrared and electronic absorption spectra reveals that the metal ions bind to the NAC molecules in 1:2 molar ratio (metal:ligand) via the S-atoms. Theoretical calculations are carried out using the B3LYP hybrid functional in combination with 6-31++G(d,p) and LANL2DZ basis sets to investigate the effects of metal coordination on the backbone structural features of NAC and geometry about the α-carbon atom. The molecular geometries of NAC as well as its metal complexes are fully optimized in gas phase without applying any geometrical constraint, and a second derivative analysis confirms that all the optimized geometries are true minima. TD-DFT single-point calculations are performed in aqueous phase to obtain the theoretical λ _max values. The gas-phase interaction enthalpies (metal ion binding affinities), Gibbs energies, HOMO/LUMO energies as well as their energy gaps, rotational constants, dipole moments, and theoretically predicted vibrational spectra of all the reaction species are also calculated and thoroughly analyzed. Most of the experimental results are well reproduced by the B3LYP level of calculations. Metal ion coordination to NAC modifies its backbone structural features as well as the geometry about the α-carbon atom.     

Real-time time-dependent density functional theory approach for frequency-dependent nonlinear optical response in photonic molecules

We present ab initio calculations of frequency-dependent linear and nonlinear optical responses based on real-time time-dependent density functional theory for arbitrary photonic molecules. This approach is based on an extension of an approach previously implemented for a linear response using the electronic structure program SIESTA. Instead of calculating excited quantum states, which can be a bottleneck in frequency-space calculations, the response of large molecular systems to time-varying electric fields is calculated in real time. This method is based on the finite field approach generalized to the dynamic case. To speed the nonlinear calculations, our approach uses Gaussian enveloped quasimonochromatic external fields. We thereby obtain the frequency-dependent second harmonic generation beta(-2omega;omega,omega), the dc nonlinear rectification beta(0;-omega,omega), and the electro-optic effect beta(-omega;omega,0). The method is applied to nanoscale photonic nonlinear optical molecules, including p-nitroaniline and the FTC chromophore, i.e., 2-[3-Cyano-4-(2-{5-[2-(4-diethylamino-phenyl)-vinyl]-thiophen-2-yl}-vinyl)-5,5-dimethyl-5H-furan-2-ylidene]-malononitrile, and yields results in good agreement with experiment.     

Photoelectrochemical kinetics of eosin y-sensitized zinc oxide films investigated by scanning electrochemical microscopy

Eosin Y is used as a sensitizer for nanoporous zinc oxide films for prospective applications in photoelectrochemical solar cells. The kinetics of the reduction of the intermittently formed photo-oxidized dye molecules by iodide ions in the electrolyte phase was investigated by using the feedback mode of scanning electrochemical microscopy (SECM). The bulk solution phase contained triiodide as electron transfer mediator, from which the ultramicroelectrode-generated iodide ions acted as electron donors for photo-oxidized Eosin Y molecules (D(+) (ads)) at the zinc oxide sample. Effective rate constants for the dye regeneration could be extracted from the SECM approach curves. The effective rate constants at different triiodide concentrations could be related to the rate constant for the reaction of the dissolved donor with photo-oxidized Eosin Y bound to ZnO, as well as to the overall rate of the photosensitization process. For the reaction D(+) (ads) + 1.5 I(-)-->D(ads) + 0.5 I(3) (-) a rate constant of k(ox) = (1.4+/-0.8)x10(8) cm(9/2) mol(-3/2) s(-1) was determined.     

紫罗碱衍生物分子结的电学性质理论研究

本文基于密度泛函(DFT)结合非平衡格林函数(NEGF)的方法,以具有氧化还原中心的紫罗碱衍生物(N,N′-bis(4-thioalkyl)-4,4′-bipyridinium, HS-4V4-SH)功能分子构造Au(111)/S-4V4-S/Au(111)分子结,详细分析了分子在三种价态V、V⁺和V²⁺下的电学性质与分子的几何结构和电子结构的关系。基于对三种价态透射系数分析结果表明,在零偏压下,V与V⁺的电导值比V²⁺高了两个数量级,4V4分子结的电导随两个吡啶环之间夹角的增大呈线性减小。同时,理论计算结果也表明,增加烷基链(HS-nVn-SH, n = 2 ~ 7)的数目,发现分子结电导值呈指数形式衰减,其每个亚甲基的衰减因子约为1,与烷基二硫醇分子的接近。