Influence of temperature and pressure on shape and shift of impurity optical bands in polymer glasses

The shape, broadening, and shift of optical absorption spectra of molecular impurity centers in polymer glasses are considered in terms of inhomogeneous energy distributions and coupling of electronic transitions to vibrations. Persistent spectral hole burning was applied for frequency-selective probing of zero-phonon lines. The shift and broadening of spectral holes were studied between 5 and 50 K and by applying a hydrostatic He gas pressure up to 200 bar. Broadband absorption spectra were recorded between 5 and 300 K in poly(methyl methacrylate) and polyethylene. In addition to "normal" thermal broadening, due to the first- and second-order electron phonon coupling, several narrowing components were predicted on the basis of frequency dependent hole behavior. Thermal expansion of the matrix and the relaxation of local strains, previously accumulated on cooling below the glass temperature can lead to shrinking of the inhomogeneous width. A Voigt treatment of absorption band shapes reveals that the Gaussian component can indeed suffer remarkable narrowing. Inhomogeneous band shapes and the frequency-dependent thermal and baric line shifts were rationalized with the aid of a pair of two-body Lennard-Jones potentials. The shift of potential well minima is a crucial factor influencing solvent shifts, inhomogeneous band shapes, pressure shift coefficients, and quadratic electron phonon coupling constants.     

Effect of solvent on absorption spectra of all-trans-beta-carotene under high pressure

The absorption spectra of all-trans-beta-carotene in n-hexane and carbon disulfide (CS(2)) solutions are measured under high pressure at ambient temperature. The common redshift and broadening in the spectra are observed. Simulation of the absorption spectra was performed by using the time-domain formula of the stochastic model. The pressure dependence of the 0-0 band wavenumber is in agreement with the Bayliss theory at pressure higher than 0.2 GPa. The deviation of the linearity at lower pressure is ascribed to the reorientation of the solvent molecules. Both the redshift and broadening are stronger in CS(2) than that in n-hexane because of the more sensitive pressure dependence of dispersive interactions in CS(2) solution. The effect of pressure on the transition moment is explained with the aid of a simple model involving the relative dimension, location, and orientation of the solute and solvent molecules. The implication of these results for light-harvesting functions of carotenoids in photosynthesis is also discussed.     

The high pressure nitric oxide mass spectra of aldehydes

The high pressure (0.5 Torr) nitric oxide mass spectra of some aldehydes, obtained using a 10% mixture of NO in N₂, are reported. The 10% NO/N₂ spectra of the monodeuterated analogs of some of them are compared to the electron-impact and methane chemical ionization spectra, especially with reference to the process of hydride abstraction by nitrosonium ions.     

High-resolution optical spectroscopy of benzophenone under high pressure

Phosphorescence spectra of benzophenone have been investigated with a diamond anvil cell. At 2 K the spectra remain sharp under high pressure. The pressure shift of the origin exhibits a plateau around 25 kbar. This and other spectral observations are interpreted.     

Effects of high pressure on optical activity induced by chiral solvents

A technique for measuring CD spectra of solutions under pressure has been developed. The positive induced CD of the n-π^* band of trans-azobenzene in (?)-bornyl acetate solution was blue-shifted by 1.7 kK and enhanced by a factor of 2.7 at 700 bar.     

Influence of high pressure processing on protein solutions and emulsions

Static high-pressure technology is likely to be used increasingly over the next few years in the preservation and processing of food. This ‘clean’ technology offers an effective and safe method of modifying protein structure, and self-assembly properties. Pressure processing can lead to globular protein denaturation, and different states of aggregation or gelation depending on the protein system, the treatment temperature, the solution conditions, and the magnitude and duration of the applied pressure.     

Influence of working load on performance of high pressure grinding rolls

辊压机在矿山领域的应用越来越广泛,为了优化辊压机的工作参数和工艺参数,以提高辊压机的工作性能,分析了辊压机的工作载荷对其工作性能的影响。结果显示,随着工作载荷的增大,消耗功率线性增加,产品粒度减小,且减小的幅度越来越小。综合考虑辊压机的工艺参数、运转稳定性和辊面磨损寿命,进而确定最佳工作载荷。     

Influence of solution composition and ultrasonic treatment on optical spectra of TiO2 aqueous suspensions

Investigation of TiO(2) aqueous suspensions has shown that their optical spectra can be unstable, with instability not related to precipitation or adherence of TiO(2) particles to the vessel walls. Increase of ionic strength of the suspension as well as neutralization of charged TiO(2) particles via pH adjustment accelerates the optical density drop. Vice versa, increasing the charge of TiO(2) particles via shifting pH in acidic or basic directions stabilizes the suspension's optical spectra, and ultrasonic treatment promotes optical density recovery. The observed behavior is attributed to alteration in the size of the suspension aggregates.     

Antiburning in impurity spectra by light-induced changes of phototransformation efficiency

The formation of stable antiholes in the absorption spectrum of octaethylporphin in polystyrene at 5 K is observed by selective light-induced depopulation of the previously non-selectively populated S₁ electronic state. The mechanism of this phenomenon and its applications in studies of phototransformation pathways and vibrational relaxation of impurity molecules in solids are discussed.     

Influence of box shape on the hard-disk pressure at high fluid density

The finiteness effects induced by periodic boundary conditions are examined for a hard-disk fluid. Besides the relatively simple N dependence there is a more complicated V dependence. Three different approaches are displayed and contrasted: (i) A rough estimate for the V dependence of the pressure, based on a theoretical equation of state. (ii) A more detailed and expensive treatment of the V dependence by a method due to Pratt and Haan, (iii) MC simulations, intending to evoke V dependence deliberately. The influence of varying box shape and particle number (N = 71.72 and 73) is investigated. All simulations have been carried out for high fluid density (packing FRACTION = 0.648). Finally, the consistency of these approaches is discussed.     

Raman spectra of high pressure phase and phase transition of polytetrafluoroethylene (teflon)

Raman spectra of phases II and III of crystalline polytetrafluoroethylene at room temperature and several pressures to 35 kbar are reported and discussed in terms of the information provided about molecular conformation, crystal structures, and the phase transition. A revised vibrational assignment is reported for phase II spectra which suggests that the 1215- and 1295-cm^?1 bands are not fundamentals but are combinations of overtones with A₁ symmetry of a cyclic group.     

The nature of optical spectra of p-terphenyl

The absorption, fluorescence and fluorescence excitation spectra of p-terphenyl (TP) crystals have been investigated. The absorption spectrum of a thin (1 μm, 5 K) crystal shows several electron transitions with a strongly and weakly developed vibrational structure. It is found that even the purest TP crystals contain a large number of uncontrolled impurities absorbing in the region 331 – 390 nm, and the crystal fluorescence spectrum reported in the literature is due to the defect-impurity emission.     

Determination of optical impurity of pregabalin by HPLC with pre-column chiral derivatization

A new method for determining the optical impurity of Pregabalin is developed. The method is based on Pregabalin, and its isomers can be derivatized with Na-5-fluoro-2,4-dinitrophenyl-5-L-alanine amide. These derivated compounds can be separated by an ordinary chromatography column (Inertsil ODS-2.5 microm, 250 mmx4.6 mm i.d.). Phosphoric acid buffer and acetonitrile (55:45, v/v) are used as mobile phase and 1.0 mL/min flow rate at room temperature. The detective wavelength is fixed at 340 nm. The results indicate that the limit of detection of R model optical impurity 1.1x10(-8) g/mL (signal-to-noise=3), accuracy, and repeatability is satisfied. Therefore, the method can be used for the quality control of Pregabalin.     

Effect of pressure and solvent on Raman spectra of all-trans-beta-carotene

The ground state Raman spectra of all-trans-beta-carotene in n-hexane and CS2 solutions are measured by simultaneously changing the solvent environment and molecular structure under high hydrostatic pressure. The diverse pressure dependencies of several representative Raman bands are explained using a competitive mechanism involving bond length changes and vibronic coupling. It is therefore concluded that (a) the in-phase C=C stretching mode plays an essential role in the conversion of energy from S1 to S0 states in carotenoids, (b) internal conversion and intramolecular vibrational redistribution can be accelerated by high pressure, and (c) the environmental effect, but not the structural distortion or pi-electron delocalization, is responsible for the spectral properties of a given carotenoid species. These findings revealed the potential of high pressure in exploring the nature of the biological functions of carotenoids.