Shift equations iteration solution to <Emphasis Type="Italic">n</Emphasis>-level close coupled equations,and the two-level nonadiabatic tunneling problem revisited

The shift equations iteration (SEI) solves the n-level quantum scattering problem in one dimension, i.e., the close-coupled equations, free from exponential instability arising from closed channels. SEI provides exponential-instability-free transmission and reflection coefficients, and is well suited to two-sided scattering problems such as conduction in molecular wires. Our most efficient implementation of SEI utilizes an adaptation of the log-derivative symplectic integrator described by Manolopoulos and Gray in (J Chem Phys 102:9214, 1995). The two-level nonadiabatic tunneling system is investigated—in the tunneling regime, above the barrier, and at resonance. Nonadiabatic components in the upper channel wavefunction (and lower channel wavefunction at resonance energies) are found to be non-adiabatic, i.e., not describable by WKB functions. Their behavior is characterized in terms of an empirical model relating these components to adiabatic components in the lower (upper) channel and the potential energy coupling.     

A path-integral Langevin equation treatment of low-temperature doped helium clusters

We present an implementation of path integral molecular dynamics for sampling low temperature properties of doped helium clusters using Langevin dynamics. The robustness of the path integral Langevin equation and white-noise Langevin equation [M. Ceriotti, M. Parrinello, T. E. Markland, and D. E. Manolopoulos, J. Chem. Phys. 133, 124104 (2010)] sampling methods are considered for those weakly bound systems with comparison to path integral Monte Carlo (PIMC) in terms of efficiency and accuracy. Using these techniques, convergence studies are performed to confirm the systematic error reduction introduced by increasing the number of discretization steps of the path integral. We comment on the structural and energetic evolution of He(N)-CO(2) clusters from N = 1 to 20. To quantify the importance of both rotations and exchange in our simulations, we present a chemical potential and calculated band origin shifts as a function of cluster size utilizing PIMC sampling that includes these effects. This work also serves to showcase the implementation of path integral simulation techniques within the molecular modelling toolkit [K. Hinsen, J. Comp. Chem. 21, 79 (2000)], an open-source molecular simulation package.     

A refined ring polymer molecular dynamics theory of chemical reaction rates

We further develop the ring polymer molecular dynamics (RPMD) method for calculating chemical reaction rates [I. R. Craig and D. E. Manolopoulos, J. Chem. Phys. 122, 084106 (2005)]. We begin by showing how the rate coefficient we obtained before can be calculated in a more efficient way by considering the side functions of the ring-polymer centroids, rather than averaging over the side functions of the individual ring-polymer beads. This has two distinct advantages. First, the statistics of the phase-space average over the ring-polymer coordinates and momenta are greatly improved. Second, the resulting flux-side correlation function converges to its long-time limit much more rapidly. Indeed the short-time limit of this flux-side correlation function already provides a "quantum transition state theory" approximation to the final rate coefficient. In cases where transition state recrossing effects are negligible, and the transition state dividing surface is put in the right place, the RPMD rate is therefore obtained almost instantly. We then go on to show that the long-time limit of the new flux-side correlation function, and hence the fully converged RPMD reaction rate, is rigorously independent of the choice of the transition state dividing surface. This is especially significant because the optimum dividing surface can often be very difficult to determine for reactions in complex chemical systems.     

Selective extraction of blood plasma exchangeable copper for isotope studies of dietary copper absorption

Measuring mineral absorption by fecal monitoring is labor-intensive and relies on good volunteer compliance. Blood indicators of absorption could be advantageous and we have developed a method for selective extraction-of recently absorbed (exchangeable) copper based on dialysis of plasma with histidine and subsequent copper extraction using Chelex resin. The potential for measuring copper absorption by transient enrichment of exchangeable copper with the stable isotope 65Cu from an ingested tracer, was also investigated. This method was compared with that of the fecal monitoring technique in a human volunteer, who consumed a 6 mg dose of 65Cu with inhibitors of copper absorption. Holmium was used as a non-absorbable rare-earth marker of unabsorbed tracer excretion, allowing estimation of re-secreted 65Cu (44 microg d(-1)), and hence calculation of true tracer absorption, which was only 10.8%. Monitoring plasma tracer kinetics showed potential for estimation of copper absorption without the need for fecal copper analysis.     

X-ray absorption near-edge spectroscopic study of nickel catalysts

Ni-isocyanide and Ni-acac complexes have been studied by X-ray absorption spectroscopy. Theoretical analysis has been done using self-consistent full multiple scattering (MS) approach within both muffin-tin (MT) model of the potential and non-MT finite deference method. For the isocyanide complex, it was shown that MS theoretical spectra reproduce all structural details of the X-ray absorption near-edge structure (XANES), but also that it is important to consider the non-MT effects in the potential for a correct simulation of the shape of the pre-edge structures. The contribution of a non-constant potential in the interstitial regions is extremely important for the interpretation of the XANES of Ni(acac)₂.     

Polarization and temperature dependent spectra of poly(3-hydroxyalkanoate)s measured at terahertz frequencies

Temperature-dependent terahertz (THz) absorption spectra of poly(3-hydroxyalkanoate)s (PHAs) were measured by using a Fourier transform far-infrared (FT-FIR) spectrometer and a THz time-domain spectrometer over a temperature range of 10 K to 465 K with a liquid helium cryostat and a heating cell. Clear differences were observed between the spectra of crystalline and amorphous polyhydroxybutyrate (PHB), indicating that the absorption peaks observed in the THz spectra originated in the higher-order conformation of PHB. The polarization spectra of a stretched PHB sample were measured, and the direction of the vibrational transition moment was determined. The temperature dependences of the spectra reveal frequency shifts and broadening of the absorption peaks with temperature, suggesting large anharmonicity of the vibrational potential. The temperature shift behaviour is quite different in each transition. Some of the transitions show a blue shift, which cannot be explained by a simple anharmonic potential model. Frequency shifts of the peaks were mainly observed below 10 THz, which suggests a large anharmonicity of the vibrational potential at lower frequencies.     

N,N′-二-(2-吡啶基)苝四羧酸二酰亚胺的合成及性能研究

合成了N,N′ 二 (2 吡啶基)四羧酸二酰亚胺,并纯化、调晶.对产物进行了元素分析和IR光谱研究(环状二酰亚胺的CO以双峰1708.8cm-1、1664 5cm-1).α晶型产物溶液的紫外可见光谱(最大吸收波长为526.00nm)和荧光光谱(最大发射波长为538.0nm)存在很好的镜像对称关系.薄膜紫外可见光谱图在450—570nm范围内,α晶型比β晶型有较强的吸收峰.X粉末衍射也反映出α晶型在2θ为25.5°、26.3°上的衍射峰强度分别为1954、2603.α、β晶型分别作为电荷产生材料制得的功能分离型有机光导体,在光源波长λ=532nm曝光下,测得含α的感光体达到饱和电位的时间45s、半衰曝光量5.7μJ/cm2、残余电位22V等数据.测得含β的感光体达到饱和电位的时间49s、半衰曝光量9.9μJ/cm2、残余电位22V等性能数值.     

Ab initio potential energy surfaces, total absorption cross sections, and product quantum state distributions for the low-lying electronic states of N(2)O

Adiabatic potential energy surfaces for the six lowest singlet electronic states of N(2)O (X (1)A('), 2 (1)A('), 3 (1)A('), 1 (1)A("), 2 (1)A(") and 3 (1)A(")) have been computed using an ab initio multireference configuration interaction (MRCI) method and a large orbital basis set (aug-cc-pVQZ). The potential energy surfaces display several symmetry related and some nonsymmetry related conical intersections. Total photodissociation cross sections and product rotational state distributions have been calculated for the first ultraviolet absorption band of the system using the adiabatic ab initio potential energy and transition dipole moment surfaces corresponding to the lowest three excited electronic states. In the Franck-Condon region the potential energy curves corresponding to these three states lie very close in energy and they all contribute to the absorption cross section in the first ultraviolet band. The total angular momentum is treated correctly in both the initial and final states. The total photodissociation spectra and product rotational distributions are determined for N(2)O initially in its ground vibrational state (0,0,0) and in the vibrationally excited (0,1,0) (bending) state. The resulting total absorption spectra are in good quantitative agreement with the experimental results over the region of the first ultraviolet absorption band, from 150 to 220 nm. All of the lowest three electronically excited states [(1)Sigma(-)(1 (1)A(")), (1)Delta(2 (1)A(')), and (1)Delta(2 (1)A("))] have zero transition dipole moments from the ground state [(1)Sigma(+)(1 (1)A('))] in its equilibrium linear configuration. The absorption becomes possible only through the bending motion of the molecule. The (1)Delta(2 (1)A('))<--X (1)Sigma(+)((1)A(')) absorption dominates the absorption cross section with absorption to the other two electronic states contributing to the shape and diffuse structure of the band. It is suggested that absorption to the bound (1)Delta(2 (1)A(")) state makes an important contribution to the experimentally observed diffuse structure in the first ultraviolet absorption band. The predicted product rotational quantum state distribution at 203 nm agrees well with experimental observations.     

Strong room-temperature ferromagnetism in Co2+-doped TiO2 made from colloidal nanocrystals

Colloidal cobalt-doped TiO(2) (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (M(s) approximately 1.5 x 10(-)(3) micro(B)/Co(2+) at 300 K) when aggregated, and strongly ferromagnetic (up to M(s) = 1.9 micro(B)/Co(2+) at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co(2+) oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO(2), these results demonstrate the possibility of using colloidal TiO(2) diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.     

Outer-sphere effects on reduction potentials of copper sites in proteins: the curious case of high potential type 2 C112D/M121E Pseudomonas aeruginosa azurin

Redox and spectroscopic (electronic absorption, multifrequency electron paramagnetic resonance (EPR), and X-ray absorption) properties together with X-ray crystal structures are reported for the type 2 Cu(II) C112D/M121E variant of Pseudomonas aeruginosa azurin. The results suggest that Cu(II) is constrained from interaction with the proximal glutamate; this structural frustration implies a "rack" mechanism for the 290 mV (vs NHE) reduction potential measured at neutral pH. At high pH (～9), hydrogen bonding in the outer coordination sphere is perturbed to allow axial glutamate ligation to Cu(II), with a decrease in potential to 119 mV. These results highlight the role played by outer-sphere interactions, and the structural constraints they impose, in determining the redox behavior of transition metal protein cofactors.     

Growth and Spectroscopic Investigations of Disordered Nd3+:Li3Ba2La3(MoO4)8 Crystal

Nd3+: Li3Ba2La3(MoO4)8 crystal has been grown from a flux of Li2MoO4 by the top seeded solution growth method (TSSG) and its structure was confirmed by X-ray diffraction. The polarized absorption spectra, fluorescence spectra and fluorescence decay curve of the crystal were measured. The main spectral parameters were calculated by the Judd-Ofelt theory and compared with other Nd-doped crystals. The broad absorption bands and the large absorption cross sections around 805 nm indicate that the crystal is very suitable for diode-laser pumping. The broad emission bands around 1060 nm show that the crystal is a potential medium for tunable and short pulse lasers. The quantum efficiency of the crystal is up to 95%, which is higher than the value for Nd3+:YVO4 and Nd3+:YAG and comparable to that of other disordered molybdate crystals. The excellent spectroscopic properties show that Nd3+:Li3Ba2La3(MoO4)8 crystal may be regarded as a potential solid state laser host material for diode laser pumping.     

Low power, biologically benign NIR light triggers polymer disassembly

Near infrared (NIR) irradiation can penetrate up to 10 cm deep into tissues and be remotely applied with high spatial and temporal precision. Despite its potential for various medical and biological applications, there is a dearth of biomaterials that are responsive at this wavelength region. Herein we report a polymeric material that is able to disassemble in response to biologically benign levels of NIR irradiation upon two-photon absorption. The design relies on the photolysis of the multiple pendant 4-bromo7-hydroxycoumarin protecting groups to trigger a cascade of cyclization and rearrangement reactions leading to the degradation of the polymer backbone. The new material undergoes a 50% Mw loss after 25 sec of ultraviolet (UV) irradiation by single photon absorption and 21 min of NIR irradiation via two-photon absorption. Most importantly, even NIR irradiation at biologically benign laser power is sufficient to cause significant polymer disassembly. Furthermore, this material is well tolerated by cells both before and after degradation. These results demonstrate for the first time a NIR sensitive material with potential to be used for in vivo applications.     

Sur la mesure in vitro de la protection solaire de crièmes cosmétiques

The protective power of sun creams is usually defined by the sun protection factor (SPF) which is derived from the creams absorption spectrum between 290 and 400 nm. The SPF is actually calculated from spectral data by applying a mathematical equation, but testing this equation on both real and hypothetical creams demonstrated that the SPF does not take into account the true absorption profile of the cream, especially in the UVA range (between 320 and 400 nm). A new index (the sun protection potential, SPP) is proposed based on the percentage of light absorbed.     

Insight into absorption of radiation/energy transfer in infrared matrix-assisted laser desorption/ionization: the roles of matrices, water and metal substrates.

Although the ionization/desorption mechanisms in matrix-assisted laser desorption/ionization (MALDI) remain poorly understood, there is a clear difference between the energy absorption processes in the ultraviolet (UV) and infrared (IR) modes of operation. UV-MALDI demands an on-resonance electronic transition in the matrix compound, whereas results presented here support earlier work showing that a corresponding resonant vibrational transition is not a requirement for IR-MALDI. In fact, data from the present study suggest that significant absorption of radiant energy by a potential matrix impairs its performance, although this observation is at variance with some other reports. For example, sinapinic acid, with an IR absorption maximum close to the 2.94 micrometer wavelength of the Er-YAG laser, has been little used as an IR-MALDI matrix. By contrast, succinic acid, with much lower IR absorption and no history of use in UV-MALDI as it has no UV absorption at the wavelength of common UV lasers, has become widely recognized as a good general purpose matrix for IR-MALDI. Despite reports by others that glycerol is an effective matrix for IR-MALDI, we find that glycerol, which also absorbs strongly at 2.94 micrometer, is useful only if applied as a very thin film. Thus the cumulative evidence for the role of the matrix in IR-MALDI appears confusing and often contradictory. Water has been postulated to be a major contributor to the absorption of energy in IR-MALDI. Consistent with this, we find that samples dried from D(2)O, which does not absorb at 2.94 micrometer, give spectra of inferior quality compared with the same samples from H(2)O. Similarly, samples dried under vacuum, that probably contain less water than those dried in the open laboratory, give weaker and more erratic spectra. Another potential participant in energy absorption and energy transfer is the surface of the metal support, an alternative mechanism for IR-MALDI, for which some evidence is presented here.     

Rational Molecular Design towards Vis/NIR Absorption and Fluorescence by using Pyrrolopyrrole aza‐BODIPY and its Highly Conjugated Structures for Organic Photovoltaics

Pyrrolopyrrole aza‐BODIPY (PPAB) developed in our recent study from diketopyrrolopyrrole by titanium tetrachloride‐mediated Schiff‐base formation reaction with heteroaromatic amines is a highly potential chromophore due to its intense absorption and fluorescence in the visible region and high fluorescence quantum yield, which is greater than 0.8. To control the absorption and fluorescence of PPAB, particularly in the near‐infrared (NIR) region, further molecular design was performed using DFT calculations. This results in the postulation that the HOMO–LUMO gap of PPAB is perturbed by the heteroaromatic moieties and the aryl‐substituents. Based on this molecular design, a series of new PPAB molecules was synthesized, in which the largest redshifts of the absorption and fluorescence maxima up to 803 and 850 nm, respectively, were achieved for a PPAB consisting of benzothiazole rings and terthienyl substituents. In contrast to the sharp absorption of PPAB, a PPAB dimer, which was prepared by a cross‐coupling reaction of PPAB monomers, exhibited panchromatic absorption across the UV/Vis/NIR regions. With this series of PPAB chromophores in hand, a potential application of PPAB as an optoelectronic material was investigated. After identifying a suitable PPAB molecule for application in organic photovoltaic cells based on evaluation using time‐resolved microwave conductivity measurements, a maximized power conversion efficiency of 1.27 % was achieved.     

Charge transfer absorption for pi-conjugated polymers and oligomers mixed with electron acceptors

Pi-conjugated polymers and oligomers show charge transfer (CT) absorption bands when mixed with electron acceptors in chloroform solution. This is attributed to the formation of (ground state) donor-acceptor complexes in solution. By varying the concentration of the donor and acceptor, the extinction coefficient for the CT absorption and the association constant of donor and acceptor are estimated. The spectral position of the CT bands correlates with the electrochemical oxidation potential of the pi-conjugated donor and the reduction potential of the acceptor.     

Exciton Coupling of Surface Complexes on a Nanocrystal Surface

Exciton coupling may arise when chromophores are brought into close spatial proximity. Herein the intra‐nanocrystal exciton coupling of the surface complexes formed by coordination of 8‐hydroxyquinoline to ZnS nanocrystals (NCs) is reported. It is studied by absorption, photoluminescence (PL), PL excitation (PLE), and PL lifetime measurements. The exciton coupling of the surface complexes tunes the PL color and broadens the absorption and PLE windows of the NCs, and thus is a potential strategy for improving the light‐harvesting efficiency of NC solar cells and photocatalysts.     

Tuning the physicochemical properties of diverse phenolic ionic liquids for equimolar CO2 capture by the substituent on the anion

Phenolic ionic liquids for the efficient and reversible capture of CO(2) were designed and prepared from phosphonium hydroxide and substituted phenols. The electron-withdrawing or electron-donating ability, position, and number of the substituents on the anion of these ionic liquids were correlated with the physicochemical properties of the ionic liquids. The results show that the stability, viscosity, and CO(2)-capturing ability of these ionic liquids were significantly affected by the substituents. Furthermore, the relationship between the decomposition temperature, the CO(2)-absorption capacity, and the basicity of these ionic liquids was quantitatively correlated and further rationalized by theoretical calculation. Indeed, these ionic liquids showed good stability, high absorption capacity, and low absorption enthalpy for CO(2) capture. This method, which tunes the physicochemical properties by making use of substituent effects in the anion of the ionic liquid, is important for the design of highly efficient and reversible methods for CO(2)-capture. This CO(2) capture process using diverse phenolic ionic liquids is a promising potential method for CO(2) absorption with both high absorption capacity and good reversibility.     

Cesium dimer spectroscopy on helium droplets

Visible absorption spectra of cesium-doped helium nanodroplets between 14,500 and 17,600 cm(-1) were probed by laser-induced fluorescence. A strong absorption band peaking around 16,700 cm(-1) is identified as Cs2 1(a) 3Sigmau+-3 3Sigmag+ transition. A broad unstructured band near 17,520 cm(-1) is assigned as the Cs2 1(X) 1Sigmag+-2 1Sigmau+ transition. Explanations of the observations are discussed on the basis of ab initio potential curves calculated by Spies and Meyer [(unpublished)]. All spectra have been modeled using narrow Frank-Condon windows around the equilibrium internuclear distance of the lowest singlet and triplet states. Many observed absorption peaks of smaller intensities could be identified, some of which may be due to transitions of cesium trimers formed on the droplets.     

Ultrasensitive absorption spectroscopy of optically-trapped aerosol droplets

High-sensitivity optical absorption measurements on individual sub-picoliter aqueous droplets are reported using aerosol optical tweezers to simultaneously manipulate and characterize a sample droplet and a control droplet for comparison. It is demonstrated that the detection sensitivity to trace analytes is set by the weak absorption by the solvent, water, and that absorbances less than 5 x 10(-7) can be measured over pathlengths of less than 10 microm. The potential applications of this approach to analyze aerosol particle composition and to perform trace analysis are discussed.