bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Fluorescence and Energy Transfer in Polystyrene under Excitation in the Vacuum Ultraviolet
Authors: Leibowitz M. , Weinreb A. 
Published: January 2005

The emission spectrum of solid polystyrene is investigated as a function of excitation wavelength in the region 2540–1216 Å, for various modes of preparation (solid machined disks, films, evaporation layers) and treatment (heating, polishing, etc.). A strong dependence of the spectral distribution on excitation wavelength is observed. Exciting radiation which is more strongly absorbed produces a fluorescence spectrum extending to longer wavelengths. A strong influence of the mode of preparation and treatment of the sample on the fluorescence spectrum is observed. The results are tentatively interpreted as representing the strong influence of the solid-state structure of the material on intermolecular interactions between segmers.
The fluorescent quantum yield of solid solutions of diphenyloxazole and of anthracene in polystyrene is investigated as a function of the excitation wavelength in the region 3164–584 Å. A strong variation of the quantum yield with excitation wavelength is observed. The results are interpreted in terms of a competition between solvent—solvent and solvent—solute interactions, the probability of each depending on excitation wavelength. The difference in behavior of solutions of PPO and solutions of anthracene is discussed.
Kinetics of Anion Exchange between Methyl Mercuric Complexes
Authors: Simpson Richard B. 
Published: January 2005

In the proton magnetic resonance spectrum of CH3HgBr or of CH3HgI, the satellites produced by 199Hg–H spin coupling are broader than in other methyl mercuric compounds. This broadening, formerly attributed to alkyl exchange, is better explained by fast relaxation of the 199Hg nuclear spin. The large quadrupole moments of bromine and iodine are probably responsible for the 199Hg relaxation.
Anion exchange of various pairs of methyl mercuric compounds (studied by the line-shape method of Gutowsky and Holm) was too fast to measure unless cyanide was one of the anions. Rate constants and heats and entropies of activation for exchange of cyanide with hydroxide, chloride, sulfite, and thiosulfate were calculated assuming an anionic attack mechanism, e.g., CH3HgCN+X−=CH3HgX+CN−. For exchange of CH3HgCN with the hydroxide complex below pH 9 or with the mercaptoacetate complex, anionic attack seems inadequate to account for the rates, so direct reaction between CH3HgCN and the other methyl mercuric compound is postulated to occur at the high methyl mercuric concentrations used in NMR.
Mechanism of the Diels—Alder Reactions of Butadiene
Authors: Benson Sidney W. 
Published: January 2005

Kinetic data on the pyrolysis of 1,5-cycloöctadiene to give butadiene and 4-vinyl cyclohexene by parallel paths are analyzed and shown to be quantitatively consistent with a common biradical precursor, the octadien−2,6,-diyl−1,8 biradical. It is further shown that these data are in excellent agreement with independent studies of the reverse reactions; pyrolysis of 4-vinyl cyclohexene to butadiene and the dimerization of butadiene. A fourth study of the pyrolysis, in solution of 1,2-divinyl cyclobutane to give butadiene, 1,5-cycloöctadiene, 4-vinyl cyclohexene, and cis—trans isomerization is shown to fit the same scheme with only minor modifications in two of the rate constants. The analysis lends support to the 12.6-kcal assignment of the allyl stabilization energy. It also resolves an apparent anomaly in the rate parameters for the reverse Diels—Alder pyrolyses of cyclohexene, 3-methyl cyclohexene, and 4-vinyl cyclohexene.
Arrhenius parameters for all the elementary rate constants are assigned and shown to be reasonable compared to similar processes. Important rotation-controlled rates in the scheme are examined and conclusions drawn about the contributions of different rotomeric forms of the biradical.
Adsorption of CO on a Tungsten (100) Surface
Authors: Anderson J. , Estrup P. J. 
Published: January 2005

The room-temperature adsorption of carbon monoxide on the (100) surface of tungsten has been studied using the techniques of low-energy electron diffraction, flash desorption, and work-function measurement.
CO is found to exist in two binding states whch have been labeled βL and βH and is desorbed from these two states at ∼1150° and ∼1380°K, respectively. At room temperature, CO appears to adsorb into the βL state, and is associated with a work-function increase Δφ which is approximately linear with coverage and amounts to +0.43 eV at saturation—a coverage of about 1.0×1015 molecules/cm2. CO in the βL states can be converted into the βH state by heating to 900°—1000°K. Associated with the latter is an ordered c(2×2) structure which, at maximum coverage—about 5.0×1014 molecules/cm2—exhibits a Δφ of −0.16 eV with respect to the clean surface.
Adsorption of CO to saturation on the c(2×2) structure appears to return the surface to a condition indistinguishable from that due to adsorption on the clean surface. A possible model for explaining this behavior is proposed.
Carrier Generation and Recombination in Anthracene
Authors: Silver M. , Sharma R. 
Published: January 2005

The hole—electron recombination coefficient, 2–3×10−6 cm3/sec, in anthracene has been determined directly by observing the decay of photogenerated carriers as a function of time. From considerations of the magnitude of the recombination, it is concluded that carrier generation can be observed only after excitation to an almost free electron band above the lowest narrow tight-binding band.
The experimental data of Castro and Hornig, and Kearns, are analyzed in terms of band-to-band transitions to this upper band. From considerations of the wavelength dependence, autoionization of the Frenkel exciton levels at these energies is shown not to be important.
Theoretical considerations predict a very small quantum yield for the band-to-band transition. A small cross section is consistent with experiment.
Radiationless Paths in the Diazines
Authors: Cohen Beverly J. , Goodman Lionel 
Published: January 2005

Fluorescence was observed from pyrazine, pyrimidine, and pyridazine and their substituted derivatives in both liquid and rigid solutions. The fluorescence was assigned as emission from the allowed singlet (n, π*) excited state. Fluorescence and phosphorescence quantum yields of pyrazine, pyrimidine, and pyridazine, their deuterated analogs, and their substituted derivatives were measured by comparison of their emission with a standard substance of known quantum yield. Intersystem crossing yields were measured by Stephenson and Hammond by a chemical quenching method. The results of these measurements are presented in Table I.
The rates of the radiationless processes, internal conversion, and intersystem crossing were calculated from the quantum-yield data. In all cases, internal conversion was found to have the fastest rate and was the process responsible for the weak fluorescence intensity in the diazines. From the deuteration and other substituent effects on the quantum yields, it was concluded that internal conversion proceeds from the allowed singlet excited (n, π*) state to a lower forbidden singlet excited (n, π*) state. Intersystem crossing between the lowest triplet state and the ground state of pyrazine and pyrimidine was found to be noncompetitive with the radiative rates. In the ortho-diazine, a different situation was observed to exist. In the latter case, deactivation of the triplet state was attributed to an intersystem crossing process to a low-lying excited singlet state. Intersystem crossing rates were shown to be largely dependent on factors other than the first-order electronic perturbation matrix element.
Infrared Spectrum of HN3 and DN3: Assignment of the Coriolis-Coupled Bending Vibrations
Authors: Levine D. M. , Dows David A. 
Published: January 2005

The complex infrared vibration—rotation spectra of hydrazoic acid and deuterohydrazoic acid from 400–1000 cm−1 have been studied. The prominent Q branches have been assigned to three Coriolis-coupled vibrational transitions. From an analysis of the observed frequencies, band origins and Coriolis constants have been determined. HN3: v3=1263.7, v5=534.2, v6=607.0, ζ36z=−0.31, ζ56z=−0.93±0.02; DN3: v4=953.8, v5=492.2, v6=588.4, ζ46z=−0.41, ζ56z=−0.82±0.02.
Coriolis coupling between v5(a′) and v6(a″), combined with the inherently small intensity of v6, causes v6 as well as v5 to exhibit predominantly parallel character. The anomalous intensity distribution has been the cause of previous difficulty in assignment.
Variational Procedure for Open-Shell LCAO Multideterminant Wavefunctions. An Approach to the Excited-State Problem
Authors: Rossi M. 
Published: January 2005

A procedure recently suggested for solving the LCAO problem is applied to open-shell LCAO wavefunctions built up by adding many determinants having the same spatial part which, commonly, are used to approximate the wavefunction of excited states.
The procedure is extended to the case when an orthogonality condition must be explicitly imposed with given wavefunctions representing lower-energy states.
Vacuum-Ultraviolet Absorption of Shock-Heated Vibrationally Excited Nitrogen
Authors: Appleton J. P. , Steinberg M. 
Published: January 2005

Absorption coefficients of shock-heated nitrogen have been measured over a temperature range from 3500° to 10 000°K at four wavelengths: 1086, 1176, 1247, and 1334 Å. The experiments were performed behind the reflected shock about 1 cm from the end wall of a 3-in-diam shock tube which was equipped with lithium fluoride windows. Light from a pulsed hydrogen discharge lamp passed across the shock tube at the window station and entered the entrance slit of a 0.5-m Seya—Namioka monochromator. The intensity at the exit slit was recorded using an oscilloscope and a photomultiplier which monitored the fluorescence emitted from a thin coating of sodium salycilate on a quartz screen which was placed immediately behind the exit slit. Absorption of the transmitted light was measured behind the reflected shock at times after vibrational equilibration but prior to significant dissociation.
The temperature dependence of the absorption coefficient obtained at each wavelength indicated that the absorption was due to photoexcitation of molecules from within one or two adjacent vibrational levels of the ground electronic state X 1Σg+ [to the b′ 1Σu+(12.849 eV)] the b 1πu(12.575 eV), and probably to other states of comparable energy. Upper limits for the values of the electronic f numbers for the b′←X and b←X transitions were deduced from the experimental data using previously calculated values of the absorption coefficients per unit f number for these bands. Approximate measurements of vibrational relaxation times at 1334 Å (v″≃13) have also been obtained which agree fairly well with the lower temperature measurements of previous investigations.
Born—Oppenheimer Separation for Three-Particle Systems. II. Two-Center Wavefunctions
Authors: Hunter G. , Pritchard H. O. 
Published: January 2005

Semianalytic solutions of the Schrödinger equation for the motion of a particle in the static Coulomb field of two other particles are derived in a form suitable for numerical evaluation of the expansion coefficients on an electronic computer. Relevant mathematical aspects and the numerical methods are described. Tables of two-center wavefunctions are made available through the American Documentation Institute.
An Appendix describes some ``dynamic scaling'' procedures, designed to facilitate Gaussian elimination and bisection where large-order matrices are involved.
Born—Oppenheimer Separation for Three-Particle Systems. III. Applications
Authors: Hunter G. , Pritchard H. O. 
Published: January 2005

The formulation of the three-body problem presented in Paper I of this series leads to a set of second-order linear simultaneous differential equations. A numerical procedure for the solution of these equations is described, and is used to compute nonadiabatic energies for the first few rotation—vibration levels of 2Σg H2+, 2Σ HD+, and 2Σg D2+. The dipole moment of 2Σ HD+ is given, together with matrix elements for rotation—vibration transitions.
The method is also applied to obtain approximate binding energies of two-electron atoms and various mesonic systems from two-center wavefunctions.
Investigation of the Low-Temperature Phase Transition in Solid Methane by Slow Neutron Inelastic Scattering
Authors: Harker Y. D. , Brugger R. M. 
Published: January 2005

Slow neutron scattering measurements have been performed on a sample of solid methane at temperatures of 5°, 9.1°, 18°, and 22.1°K. The objective of these measurements was to try to observe differences in the spectra of neutrons scattered from the three phases of solid CH4 above and below the two transition temperatures at 8° and 20.4°K. Whereas definite differences were not observed above and below the 8°K transition, the spectra of scattered neutrons displayed significant changes above and below the 20.4°K transition. The most dramatic differences are in the elastic scattering peakwidths which are narrow and momentum change independent for the two low-temperature phases, while the widths of these peaks for the 22°K data are broader and broaden with increasing momentum change. A comparison of the 22°K data with ``Griffing's discrete rotation gas model'' discounts the possibility of free rotational motion existing at this temperature.
The inelastic scattering data for all four temperatures were fit with calculated curves generated from adjusted frequency spectra. These spectra do not display such dramatic differences as are observed in the elastic peaks. The spectra for the sets of data at the three lower temperatures do show more structure than the spectrum from the 22°K data with peaks at approximately ℏω=6, 9, and 12 meV.
Heavy-Atom and Substituent Effects on S—T Transitions of Halogenated Carbonyl Compounds
Authors: Borkman Raymond F. , Kearns David R. 
Published: January 2005

The low-lying S0→S and S0→T transitions in six substituted benzophenones and three carboxylic acid bromides have been investigated by direct absorption, phosphorescence excitation, and phosphorescence emission techniques in rigid media. In several bromine-substituted benzophenones, the oscillator strength of the S0→Tn,π transition was found to be larger by a factor of 2 to 3 than in benzophenone. However, comparison with methyl- and chlorosubstituted benzophenones indicates that this enhancement is probably due to a substituent effect rather than a specific heavy-atom effect. There was no intermolecular heavy-atom enhancement of S0→Tn,π transitions. Similar results were obtained, with acetophenone
The absorption and phosphorescence spectra of benzoyl bromide were measured, and it was concluded that the lowest triplet state of this compound is of (π, π) type.
The weak (ε=1.8) 4300-Å absorption band in oxalyl bromide has been reinvestigated. Studies of solvent effects on the absorption spectrum of oxalyl bromide and of the phosphorescence excitation spectrum of oxalyl bromide in rigid glass solutions containing naphthalene or phenanthrene confirm the assignment of the 4300-Å band as an S0→Tn,π transition. The strength of the transition ε=1.7±0.1 is, however, anomalously high as compared to all other known S0→Tn,π or S→Tπ,π transitions in organic molecules containing bromine as the heaviest atom.
Measurement of Lifetimes and Quenching Cross Sections of the B State of I2
Authors: Chutjian Ara , Link John K. , Brewer Leo 
Published: January 2005

The phase-shift method was used to measure lifetimes of selected vibrational regions from v′=10 to v′∼100, together with self-quenching collision cross sections, of the B3Π0+u state of I2.
The reliability of the method was confirmed by good agreement with other measurements for the lifetime of the mercury 3P1 state. At high optical densities, the observed increase in lifetime was shown to be due to radiation entrapment.
Reasonable agreement was found between the lifetime values and absorption measurements, but, contrary to expectations, the self-quenching cross sections varied only a factor of 1.3 with vibrational excitation whereas the lifetimes varied by as much as a factor of 8.
The substantial variation of lifetime with v′, which cannot be merely a wavelength effect, indicates either that spontaneous predissociation of the B state of I2 is an important process which has a rate at least as great as that for radiative decay and which varies considerably with v′ or that the transition moment is changing with vibrational stretching.
Spectroscopic Temperature Measurements on Laser-Produced Flames
Authors: Mentall J. E. , Nicholls R. W. 
Published: January 2005

Time-integrated spectroscopic intensity measurements have been made on the flame produced by the interaction of a focused ruby laser with powdered solids. Target materials used were Ba(AlO2)2, CaS, C, and Al microspheres.
Excitation temperatures of 24 000° and 9000°K have been inferred from the Ba and Ca spectra. Vibrational and rotational temperatures for AlO, C2, and CN were found to lie in the range of 3600° to 5600°K.
It is probable that excitation of the atomic and molecular spectra result from collisions between the emitting species and free electrons which have been superheated by absorption of a small fraction of the laser-beam energy.
Electron Paramagnetic Resonance Spectra of Two Zinc-Doped and Nickel-Doped Copper Chloride Pyridine-N-Oxide Complexes
Authors: Kokoszka Gerald F. , Allen Harry C. , Gordon Gilbert 
Published: January 2005

The electron paramagnetic resonance spectra of zinc-doped dichlorobispyridine-N-oxide copper(II) [(C5H5NO)2Cu(Zn)Cl2] and zinc-doped dichloromonoaquopyridine-N-oxide copper(II) [C5H5NOCu(Zn)Cl2·H2O] have been observed at liquid-nitrogen temperature. The data could be fit to the usual S=½ spin Hamiltonian. The g values obtained in this study for the copper—zinc pairs agree with the g values obtained for the copper—copper pairs in the pure material to within experimental uncertainty. Copper hyperfine splittings and chlorine superhyperfine splittings were also observed. The magnetic parameters for (C5H5NO)2Cu(Zn)Cl2 are gz=2.323, gx=2.056, gy=2.080, Az=129×10−4 cm−1, Ax=Ay&lt;10×10−4 cm−1, A′=25×10−4 cm−1, and B′=7×10−4 cm−1, while for C5H5NOCu(Zn)Cl2·H2O gz=2.306, gx=2.056, gy=2.083, Az=139×10−4 cm−1, and Ax=Ay&lt;10×10−4 cm−1 obtain. An analysis of the data with a simple LCAO MO approach suggests relatively strong metal—ligand bonds.
The data obtained from the study of nickel-doped (C5H5NO)2CuCl2 could be fit to an S=½ spin Hamiltonian with the following magnetic parameters: gz=2.14, gx=2.54, gy=2.49, Az=35×10−4 cm−1, and Ax=Ay&lt;7×10−4 cm−1. For nickel-doped C5H5NOCuCl2·H2O. gz=2.15, gx=2.61, gy=2.50, Az=40×10−4 cm−1, and Ax=Ay&lt;7×10−4 cm−1 were observed. These appear to be the first reported magnetic parameters from dimers which contain exchange-coupled dissimilar transition-metal ions.
Serum antibodies to collagen XIII: a further good marker of active Graves’ ophthalmopathy
Authors: De Bellis A. , Sansone D. , Coronella C. , Conte M. , Iorio S. , Perrino S. , Battaglia M. , Bellastella G. , Wall J. R. , Bellastella A. , Bizzarro A. 
Published: January 2005

objective  In Graves’ ophthalmopathy (GO) intercellular adhesion molecule‐1 (ICAM‐1) is thought to play a key role in lymphocyte infiltration into the orbit, and serum levels of its soluble form are positively correlated to clinical activity score (CAS). Serum antibodies against collagen XIII (CollXIIIAb), a plasma membrane protein expressed at a low level in almost all connective tissue‐producing cells, have been detected in GO, but their significance is unclear. The aim of this study was to search for CollXIIIAb in Graves’ patients with and without ophthalmopathy and to correlate their levels with CAS and with serum soluble ICAM‐1 (sICAM‐1) values.patients  We studied 66 patients with Graves’ disease whose sera had been previously tested for sICAM‐1 levels, grouped as follows: 28 with moderate and active ophthalmopathy (group 1), 12 of them hyperthyroid (group 1a) and 16 euthyroid (group 1b); 13 with mild and inactive ophthalmopathy and normal thyroid function (group 2); 25 without ophthalmopathy (group 3), 11 of them hyperthyroid (group 3a) and 14 euthyroid (group 3b). Finally, 26 sera of normal controls were studied.measurements  CollXIIIAb were evaluated by an enzyme‐linked immunosorbent assay (ELISA) method.results  In group 1 patients, CollXIIIAb were detected at high levels in 8/12 (66·6%) in group 1a [optical density (OD) ranging from 0·529 to 0·894] and in 10/16 (62·5%) in group 1b (OD 0·560–0·855). In group 2 patients, CollXIIIAb were detected but at low levels (OD 0·205–0·260) in 4/13 patients (30·7%). In group 3 patients, CollXIIIAb were present at low levels in 6/11 (54·5%) of group 3a and in 5/14 (35·7%) of group 3b (OD 0·215–0·290 and 0·144–0·245, respectively). CollXIIIAb were detected in only 4/26 normal controls (15%) but at low levels (OD 0·150–0·185). CollXIIIAb values in both groups 1a and 1b were significantly higher than those of the remaining groups. A positive correlation between CollXIIIAb levels and CAS but not thyroid hormone levels was found in groups 1a, 1b and 2. Moreover, a positive correlation between CollXIIIAb levels and sICAM‐1‐values was also evidenced in all three groups.conclusions  Our results suggest that CollXIIIAb could be considered as a further good marker of active inflammatory processes involving the adipose connective tissue in GO. In particular, the high levels of CollXIIIAb in sera of Graves’ patients with active ophthalmopathy could reflect an increased expression of type XIII collagen on the membrane of activated fibroblasts in these patients. Thus, the evaluation of these antibodies could be added to other known markers as a useful and inexpensive tool in monitoring Graves’ patients and in modulating the treatment of GO.