Spin dephasing in impurity induced states in molecular solids

Spin coherence experiments are used to determine the energy level structure, physical geometry, and exciton dynamics of a series of impurity-induced traps in 1,2,4,5-tetrachlorobenzene. The trap, a pertubed host molecule, is shown to be caused by an adjacent, translationally equivalent chemical impurity whose triplet energy may lie above or below the host exciton, but above the trap. The slow rates of thermal processes within the trap are interpreted as weak coupling between the lattice phonons and localized phonons induced at the trap by the impurity.     

Study of molecular orientational states of ferroelectric liquid crystals in a surface stabilized geometry

The molecular orientational states of homogeneously aligned, helix unwinding, chiral smectic C liquid crystals placed in a thin cell (surface-stabilized ferroelectric liquid crystals [SSFLC]) were studied. They were classified by the optical viewing conditions and the relationship between the directions of the chevron layer structure and the surface pretilt. The molecular orientational models of the states were considered and illustrated with regard to the experimental results. The models of molecular orientation give us a total understanding of the orientational states which appear in SSFLCs with parallel rubbing. Furthermore, the effect of the surface pretilt angle on the orientational and optical properties of SSFLCs is discussed.     

Mass spectrometric and gas and high-performance liquid chromatographic behaviour of an impurity in 2,5-hexanedione

The analysis of 2,5-hexanedione, a metabolic compound of several industrial solvents, is normally carried out using gas chromatographic (GC) or GC-mass spectrometric (MS) techniques. This work, with the aim of verifying the possibility of determining the diketone by means of a high-performance liquid chromatographic (HPLC) method with UV detection, illustrates the importance of the choice of a 2,5-hexanedione standard for the determination of the diketone response factor. In some commercial diketone samples the presence of an impurity, which may interfere with the analysis of the target analyte, was ascertained. This impurity showed GC and HPLC behaviour similar to that of 2,5-hexanedione, but gave a very different UV response. This impurity was identified as 3-methylcyclopent-2-enone by means of MS, GC-MS, HPLC-photodiode-array detection, IR and UV spectrometry. The structure was confirmed by comparing the chromatographic, mass and ultraviolet data of the unknown compound with those of a synthesized reference sample. The well known difficulty in determining 2,5-hexanedione by HPLC with UV detection was reconfirmed owing to its low molar absorptivity.     

Two-electron theory of non-interacting surface and impurity states

Some earlier results in the Davison-Cheng two-electron theory of surface and impurity states are corrected. Although the surface spin state findings are only slightly modified, it is found that the inner and outer impurity spin states no longer always occur separately, but can in fact co-exist. After discussing the connection between the two-electron theory of monatomic crystals and the one-electron theory of diatomic crystals, the paper concludes by briefly outlining the recent developments in the one-electron theory of surface and impurity state interaction.     

Dynamic changing features of the molecular face for interaction of a rare gas atom with a hydrogen molecule

We perform a systematical investigation on the dynamic changing feature of the molecular shape and size and electron density distribution in the process of a rare‐gas atom (He, Ne, Ar, and Kr) approaching a hydrogen molecule by an ab initio method. In terms of the molecular face (MF) theory, the polarization effect in the above processes is vividly demonstrated. There is a good linear correlation between our average variation rate (S_aver) of molecular intrinsic characteristic radius at the contacting point and the experimental polarizability of the rare‐gas atoms. This indicates that the MF theory can well represent the intermolecular polarization effect. Interestingly, the pictures of shape changing, charge‐flow, and exchange repulsion processes especially on the reacting active areas have been clearly observed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The d-electron states of iron group impurity atoms in silicon

The question of the relative arrangement of the crystalline terms is considered, within the framework of crystal field theory, as a function of the location of the impurity atom in the silicon. The results of the corresponding calculations are found to agree with the experimental data.     

Critical resistivity in impurity doped binary liquid mixtures

The electrical resistance of the critical binary liquid system C₆H₁₂₊(CH₃CO)₂O is measured both in the pure form and when the system is doped with small amounts (≈ 100 ppm) of H₂O impurities. Near T_c, the resistance varies as dR/dT = A₁+A₂ (T-T_c)^-b with b ≈ 0.35. Neither the critical exponent b nor the amplitude ratio A₁/A₂ are affected by the impurities. A sign reversal of dR/dT is noticed at high temperatures T ? T_c.     

Measuring polarizability anisotropies of rare gas diatomic molecules by laser-induced molecular alignment technique

The polarizability anisotropies of homonuclear rare gas diatomic molecules, Ar(2), Kr(2), and Xe(2), are investigated by utilizing the interaction of the induced electric dipole moment with a nonresonant, nanosecond laser pulse. The degree of alignment, which depends on the depth of the interaction potential created by the intense laser field, is measured, and is found to increase in order of Ar(2), Kr(2), and Xe(2) at the same peak intensity. Compared with a reference I(2) molecule, Ar(2), Kr(2), and Xe(2) are found to have the polarizability anisotropies of 0.45 ± 0.13, 0.72 ± 0.13, and 1.23 ± 0.21 A?(3), respectively, where the uncertainties (one standard deviation) in the polarizability anisotropies are carefully evaluated on the basis of the laser intensity dependence of the degree of alignment. The obtained values are compared with recent theoretical calculations and are found to agree well within the experimental uncertainties.     

Effect of molecular structure on fragmentation of isolated organic molecules in solid rare gas matrices

The effect of excess energy on the primary radical cations of bifunctional carbonyl compounds and aliphatic alkynes was simulated by matrix isolation method using rare gas matrices with various ionization potentials. The formation of fragmentation products was monitored by EPR and FTIR spectroscopy. It was shown that the radical cations of bifunctional compounds (CH₃OCH₂COCH₃ and CH₃COCOCH₃) dissociated effectively yielding CH₃ radicals upon irradiation in solid argon matrix at T≤16 K. In addition to isolated methyl radicals, the radical pairs consisting of two methyl radicals separated by two CO molecules were detected in the case of diacetyl. The probability of fragmentation decreases with the decreasing excess energy by switching from Ar to Xe. In general, bifunctional molecules were found to be less stable to “hot” ionic fragmentation in low-temperature solids in comparison with simple prototype compounds. In the case of alkynes of the RCCH type, a noticeable yield of fragmentation products was observed when R=–C(CH₃)₃, but it was negligible for R=–CH₃. The mechanisms of “hot” reactions and excess energy relaxation are discussed.     

Experimental observation of Wannier-Mott impurity ground states in an amorphous medium

The experimental observation of Wannier-Mott impurity ground states in an amorphous material is reported.     

Analysis of the gas states at a liquid/solid interface based on interactions at the microscopic level

The states of gas accumulated at the liquid/solid interface are analyzed on the basis of the continuum theory, in which the Hamaker constant is used to describe the long-range interaction at the microscopic scale. The Hamaker constant is always negative, whereas the "gas" spreading coefficient can be either negative or positive. Despite the complexity of gas, including that the density profile may not be uniform due to absorption on both solid and liquid surfaces, we predict three possible gas states at the liquid/solid interface, that is, complete "wetting", partial "wetting", and pseudopartial "wetting". These possible gas states correspond, respectively, to a gas pancake (or film) surrounded by a wet solid, a gas bubble with a finite contact angle, and a gas bubble(s) coexisting with a gas pancake. The typical thickness of the gas pancakes is at the nano scale within the force range of the long-range interaction, whereas the radius of the gas bubbles can be large. The state of a gas bubble(s) coexisting with a gas film is predicted theoretically for the first time. Our theoretical results can contribute to the development of a unified picture of gas nucleation at the liquid/solid interface.     

Classification of molecular states

Conclusions Here we will formulate briefly a member of advantages of the chain of groups in comparison with the CNPI group. In particular, the chain of groups makes it possible to do the following: 1) to carry out an unambigous classification of molecular states (when operating with the CNPI group, several classifications that differ formall from each other can be constructed); 2) to follow easily the evolution of any physical quantity characterizing the molecule, depending on the approximation [5]; 3) to avoid writing in explicit form the wavefunctions of the zero approximation and to avoid calculating the action of the symmetry elements on these functions; and so on. But the most important advantage is that the approach based on the chain of groups does not encounter any ideological difficulties in the classification of molecules for which important symmetry elements cannot be represented in the form of elements of the CNPI group.Institute of Applied Physics, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 15–22, March–April, 1992.     

Evaluation of a capillary gas chromatographic impurity test procedure for 4-hexylaniline

A capillary gas chromatographic test procedure for the detection and quantitation of impurities in the bulk intermediate, 4-hexylaniline, is evaluated and found to be accurate and precise. 4-Hexylaniline is dissolved in methanol and chromatographed isothermally at a temperature of 195 degrees C on a 60-m x 0.32-mm 85% polyethylene glycol-15% dimethylsilicone blend (DX-4) film column. A flame ionization detector is used, and the impurities in the parent compound are estimated from peak areas on a percent basis compared with the area of the parent peak in the chromatogram. Response factors are determined for the known impurities. Validation of this test method includes a recovery study of known impurity spiked samples fortified in the range of 0.1-1% (w/w). A repeatability study is performed, consisting of the analysis of two different synthetic batch lots of 4-hexylaniline analyzed over three experimental run days using two chromatographic columns of different manufacturing lots. These data and other aspects of this test procedure are discussed.     

X-ray diffraction and molecular simulation study of the crystalline and liquid states of succinic anhydride

The crystal structure of succinic anhydride was studied at five temperatures between 100 K and the melting point by single-crystal X-ray diffraction. The temperature dependence of molecular libration tensors was determined. Intermolecular interactions, in particular through unusually close molecule-molecule contacts, are discussed, with a detailed calculation of electrostatic energies. A method for the adaptation of existing crystal force fields to molecular dynamics has been developed; the adapted force field was used to study molecular motion and rotational diffusion with increasing temperature. Equilibration of the crystalline system becomes impossible at a temperature very close to the experimental melting temperature, where a sudden transition to the liquid state occurs, and a partial kinetic picture of the melting process is obtained. After validation of the force field against experimental crystal data, the state equation of the liquid was predicted. Enthalpies of sublimation, melting, and vaporization were calculated. The dynamics of a solution of succinic anhydride in a nonpolar solvent was simulated, for a discussion of the aggregation process leading to demixing and to crystal nucleation.     

Cyanex 923 as the extractant in a rare earth element impurity analysis of high-purity cerium oxide.

In this work, the feasibility of employing Cyanex 923 as an extractant into the non-cerium REE (rare earth elements) impurity analysis of high-purity cerium oxide was investigated. Through investigations on the choice of the extraction medium, the optimium extraction acidity, matrix Ce4+ effect on the non-cerium REE ion extraction, the optimium extractant concentration and suitable extracting time, and oscillation strengh, it was found that when the phase ratio was at 1:1 and the acicidity was about 2% H2SO4, by gently shaking by hand for about 2 min, 10 mL of 30% Cyanex 923 could not extract even for a 20 ng amount of non-cerium REE3+ ions. However, the extraction efficiency for Ce4+ of 100 mg total amount under the same conditions was about 96%, indicating that a 25-fold preconcentration factor could be achieved. Thus, it was concluded that Cyanex 923 could be used in a REE impurity analysis of 99.9999% or so pure cerium oxide for primary sepapation to elimilate matrix-induced interferences encountered in an ICP-MS (inductively coupled plasma mass spectroscopy) determination.     

Localized impurity states in the Hartree-Fock,LCAO approximation. I.

One-electron energies and wave functions for deep trap impurity electrons in a crystal are calculated by the Hartree-Fock, single determinant method. The interactions arising from a many-electron single determinant crystal wave function, with automatic inclusion of exchange effects, are those which determine the one-electron functions and energies. The crystal plus impurity system has no translational symmetry and hence the Bloch theorem is not applicable for the solution of the essentially infinite Hartree-Fock eigenvalue matrix. Thus we develop a technique in which the Hamiltonian and overlap matrices are written in terms of bordered matrices, with the interaction of the impurity functions with the rest of the crystal environment contained in the bordering rows and columns. The resulting secular equation explicitly includes the effects of orthogonalization of the entire basis set, including the impurity functions. This technique could be used in an iterative calculation of the electronic structure of a small number of electrons, assuming that the rest of the electrons in the environment are fixed according to an initial estimate.