bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Spectra of Orientationally Disordered Crystals. II. Infrared Spectrum of Ice Ih and Ice Ic from 360 to 50 cm−1
Authors: Bertie J. E. , Whalley E. 
Published: January 2005

The far-infrared spectra in the range 360–50 cm−1 of ice Ih and ice Ic made from H2O and from D2O, and of vitreous ice made made from H2O have been investigated. The spectra are due to essentially purely translational vibrations, and have been interpreted using the theory of the spectra of orientationally disordered phases developed in the preceding paper. There are peaks at 229.2 and 164 cm−1 that are due (in ice Ic) to maxima in the density of vibrational states due to the transverse optic and longitudinal acoustic vibrations, respectively, and a shoulder at 190 cm−1 due to the maximum in the longitudinal optic vibrations. There is also a peak just below 50 cm−1 in the spectrum of optical density divided by the square of the frequency that is due to the maximum in the transverse acoustic vibrations. Corresponding assignments are proposed for ice Ih. The Raman spectrum can in principle yield similar information, and agrees with the infrared spectrum in so far as the measurements can be compared.
Some of the observed frequencies can be fitted reasonably well with a simple nearest-neighbor bond-stretching and angle-bending potential field, but there is absorption at sufficiently high frequencies to indicate that long-range forces are important in determining the translational lattice vibrations of ice. The effects of temperature and of deuterium substitution on the spectrum are discussed.
Performance of a New Photoelectric Detection Method for Optical Spectroscopy. II. Application to Laser Raman Spectroscopy
Authors: Griffiths James E. , Pao Yoh-Han 
Published: January 2005

The application of a new ac photoelectric detection method to laser Raman spectroscopy is described. Chlorine isotope fine structure in HCCl3, CCl4, SiCl4, GeCl4, and SnCl4 is well resolved and the relative intensities of the individual isotope lines revealed an unusual liquid-state interaction in SiCl4. Such interactions are absent at room temperature in the other molecules of this type.
Spectra of CS2, ν1 and ν2, and the ν2 line of 12C6H6 and 12C513CH6 are also presented. A survey scan of the Raman spectrum of the SnCl4 using narrow slit openings demonstrates some of the advantages of the present detection method.
Near-Molecular Hartree—Fock Wavefunction for CH3+
Authors: Kari R. E. , Csizmadia I. G. 
Published: January 2005

Ab initio LCAO MO SCF calculations have been performed on CH3+ with a C–H bond length of 1.95 Bohr a.u., using Gaussian-type functions (GTF) as the basis set. By successive increases in the size of the basis set (N) of GTF's (N=12, 20, 28, 36, 40) it was possible to approach the molecular Hartree—Fock limit within 0.03 Hartree a.u. The best calculated total energy was −39.21726 hartrees while the Hartree—Fock limit has been estimated to be −39.243 hartrees for the above C–H distance.
The variation of the geometry of CH3+ indicated that the molecule is planar in its ground state and has an extensive electron delocalization. The charge distribution was such that there was approximately 0.13 positive charge on the carbon atom and 0.29 positive charge on each of the three hydrogen atoms. Due to its symmetry, the planar molecule possessed zero dipole moment but it assumed finite values in pyramidal conformations. The total electron density as well as the near Hartree—Fock molecular orbital densities are presented in the form of contour maps.
Within the framework of a single Slater determinantal wavefunction, estimations for some of the low-lying electronic excited states of CH3+ have been made.
Role of Singlet Excited States of Molecular Oxygen in the Quenching of Organic Triplet States
Authors: Kawaoka Kenji , Khan A. U. , Kearns David R. 
Published: January 2005

The quenching of triplet-state molecules by molecular oxygen is examined theoretically. Two different quenching processes are considered: namely, (i) quenching by transfer of electronic excitation energy from the triplet state of the donor molecule to oxygen, resulting in a ground-state donor molecule and an electronically excited singlet-state oxygen molecule; and (ii) quenching by enhancement of intersystem crossing in the donor molecule, resulting in a vibrationally excited donor molecule in its ground electronic state and a ground-state molecule. The relative importance of these two quenching processes is determined almost entirely by Franck—Condon factors, rather than by electronic factors. From our analysis we conclude that quenching by transfer of electronic excitation energy from the triplet-state molecule to oxygen is usually 100–1000 times faster than quenching by enhanced intersystem crossing.
Exchange interactions appear to be less important in promoting the radiationless transitions than do interactions involving charge-transfer virtual states. The absolute value of the quenching rate calculated for the energy transfer process satisfactorily accounts for the experimental observations on the oxygen quenching of triplet-state molecules in solution. These theoretical results give strong support to the previous suggestion that quenching of triplet-state molecules by oxygen leads to the production of electronically excited singlet-state (1Σg+ or 1Δg) oxygen molecules.
Bond Lengths in the α-Ga2O3 Structure and the High-Pressure Phase of Ga2−xFexO3
Authors: Marezio M. , Remeika J. P. 
Published: January 2005

The crystal structure of α-Ga2O3, which is isostructural with α-corundum, has been refined from single-crystal x-ray diffraction data. The bond lengths have been determined to an accuracy of about 0.01 Å.
The bond lengths in the GaO6 octahedron are 2.077 and 1.921 Å. The short Ga–O distance corresponds to the oxygens forming the unshared face of the octahedron, whereas the long one corresponds to the shared face.
Under high pressure and high temperature Ga2−xFexO3 undergoes a phase transition. The room-temperature, room-pressure phase is orthorhombic. In this structure the gallium ions have coordination numbers 4 and 6 while the iron ions have coordination number 6 only. The high-temperature, high-pressure phase is isostructural with α-corundum so that all cations have coordination number 6.
Raman Spectral Studies of Intermolecular Coupling in Aqueous Selenious Acid Solutions
Authors: Walrafen G. E. 
Published: January 2005

Polarized argon-ion laser and unpolarized mercury-excited photoelectric Raman spectra, and infrared spectra, were obtained for aqueous selenious acid solutions ranging in concentration from ∼1–13M at 25°C. Relative integrated Raman contour intensities, and Raman and infrared contour frequencies were obtained. Relative integrated Raman—Gaussian-component intensities, and Raman and infrared Gaussian-component frequencies were also obtained by means of a special-purpose analog computer.
Relative integrated Raman contour intensities obtained with unpolarized excitation were found to fit an equation of the form I=aM2+bM for valence and deformation contours where I is the intensity, and M the stoichiometric H2SeO3 molarity. Relative integrated Raman intensities of Gaussian valence components from unpolarized spectra were also found to show the quadratic concentration dependence.
Frequencies from polarized and unpolarized valence contours, as well as frequencies of Gaussian valence components from unpolarized Raman spectra, also indicated quadratic concentration dependences. Frequency differences between polarized and unpolarized valence contours, and between Gaussian valence components from unpolarized Raman spectra indicated quadratic concentration dependences as well.
The quadratic intensity dependences were described by the term coupling intensification, because the molar intensities were found to increase in general with M, i.e., I/M=aM+b. The quadratic frequency dependences were described by the term coupling frequency shifting. The quadratic frequency differences constitute a splitting and they were termed coupling splitting. The use of the term coupling refers to intermolecular in-phase and out-of-phase coupling between H2SeO3 vibrations. The predominant coupling mechanism was found to involve hydrogen bonding through water between the coupled H2SeO3 molecules, as evidenced by the persistence of the characteristic out-of-phase coupled component at all concentrations.
Vapor Pressures of the Methylacetylenes, H3CCCH, H3CCCD, D3CCCH, and D3CCCD
Authors: Van Hook W. Alexander 
Published: January 2005

The vapor pressures of the four deutero—protio isomers of methylacetylene of C3v symmetry have been measured over the temperature range 167° to 255°K (∼1 mm C3H4 to ∼1000 mm C3H4) by mercury monometry. Methyl-d3-acetylene shows an inverse vapor-pressure isotope effect which amounts to about 1.6% per deuterium atom at 167°K falling to 1.2% per deuterium atom at 255°K, while methylacetylene-d displays a normal effect of about 2.0% at 167°K which falls to an inverse effect of 0.2% at 255°K. The crossover temperature is near 226°K. The effect observed for D3CCCD is slightly less than the sum of the effects of D3CCCH and H3CCCD.
The data are interpreted in the light of the statistical theory of isotope effects in condensed systems. A model calculation is made in the framework of this theory in the harmonic-cell approximation using reasonable force fields. It is shown, as in the previous study on ethane, that anharmonicities in the lattice frequencies must be postulated in order to rationalize the vapor-pressure effects observed for the deutero methyl compounds. The vapor pressure of the deutero methynic compound appears unusual and it will be shown that the data indicate considerable molecular association in the condensed phase, and that the amount of this association is temperature dependent. This last point is in agreement with the results of an independent NMR investigation and with spectroscopic studies.
Nuclear Magnetic Relaxation in Ionic Solution. II. Relaxation of 23Na in Aqueous Solutions of Various Diamagnetic Salts
Authors: Eisenstadt Maurice , Friedman Harold L. 
Published: January 2005

The β coefficients in the equation T1−1—T10−1=Σβscs, which represents the nuclear relaxation rate of 23Na+ in dilute aqueous solutions at 25° as a function of solute molarity, have been determined for a variety of ionic solutes and separated into cationic and anionic contributions. For many species β is simply expressed in terms of viscosity and volume effects. Large additional contributions to β are found for a group of symmetrical, singly charged oxy and fluoro anions of which ClO4=, studied in the previous paper, is typical. The same is true for ions such as SO4= and PO4−3 for which extra interaction (such as association) with Na+ has been deduced from other types of measurements. For some solutes, including sucrose, nonlinear contributions to T1−1 dominate at concentrations as low as 0.2M. In the case of SO4= the observed nonlinearity may be attributed to ion association, in which case a dissociation constant (molar scale) of 0.2, in agreement with the result of Davies may be deduced from the data if his activity-coefficient approximation is used.
The temperature dependence of T10−1 is found to be markedly different from that for a group of relaxation and transport coefficients (e.g., proton T1 and viscous flow), all of which have nearly common behavior. It is concluded from this that the strength of the 23Na+–H2O quadrupolar interaction that determines T10 is temperature dependent. By contrast, the temperature dependence of the β for the 23Na+–ClO4− interaction exhibits the common behavior.
Approximate values of the β coefficients for the relaxation of 79Br− and 127I− are extracted from linewidth measurements on aqueous solutions of their salts reported by Hertz and Richards and co-workers. With allowance for differences in nuclear properties they are of similar magnitude and range as those for 23Na+. Structure-breaking cations give large β coefficients in these systems just as structure-breaking anions do with 23Na+.
Electronic Spectrum of Single Crystals of Ferricytochrome-c
Authors: Eaton William A. , Hochstrasser Robin M. 
Published: January 2005

The absorption spectrum of crystalline horse-heart ferricytochrome-c was investigated. Measurements were made on single crystals at room temperature from 3700 to 7600 Å using a microspectrophotometer. Molar extinction coefficients for light parallel and perpendicular to the fourfold c crystallographic axis are given.
The Soret band (4100 Å) and main visible band (5300 Å) were found to have the same polarization, while the weaker band at 5650 Å is polarized differently. These transitions are discussed in terms of the molecular orbital theory for simple metalloporphyrin complexes. Assuming the Soret and main visible bands correspond to transitions to an Eu state, the angle that the normal to the porphyrin plane makes with the c axis is calculated from the polarization ratios to be 72°. Using this angle the isotropic extinction coefficients calculated from the crystal data agree well with the extinction coefficients for these bands in solution.
The weak band at 6950 Å is polarized out of the porphyrin plane and is tentatively ascribed to the promotion of an electron from the porphyrin a2u(π) orbital to the iron a1g(dz2) orbital. The intensity of this band has been shown to be dependent on the conformation of the polypeptide. The proposed mechanism for this transition indicates two different ligand-heme configurations in ferricytochrome-c which are consequent upon the two ``conformational isomers'' postulated by Schejter and George.
It is concluded that hemoproteins provide a near perfect example of an oriented gas of chromophores.
Low-Energy Electron-Diffraction Study of the Clean (100), (111), and (110) Faces of Platinum
Authors: Lyon H. B. , Somorjai G. A. 
Published: January 2005

The structures of the (111), (100), and (110) crystal faces of platinum were studied as a function of temperature in the range 300°—1769°C (melting point). The (111) and (100) substrates are stable while the (110) face shows faceting above 600°C. Several surface structures were found to exist on the stable platinum substrates. These have well-defined temperature ranges of stability. There are two types of surface structures, ordered and disordered. Both types appear to be the property of the clean platinum substrates. The ordered structures appear during annealing, after ion bombardment at lower temperatures (&lt;900°C). They exhibit long-range order and their stability ranges overlap on a given substrate. These structures are believed to be due to ordered arrays of vacancies in the substrate plane which, under proper conditions, show remarkable stability. A high, nonequilibrium concentration of defects at the surface may be necessary to induce their formation.
The disordered surface structures appear at high temperatures, above the stability range of most of the ordered structures. They are characterized by ringlike diffraction features which develop gradually as a function of increased heating time or temperature. The formation of these structures is irreversible and they can only be removed by ion bombardment. Near the melting point, the ring patterns remain the only diffraction features of the presumably greatly disordered surfaces.
The ratio of lattice parameters assigned to the diffraction rings on each substrate indicate that they can be due to domains of (111) surface structures. These hexagonal structures appear on all of the platinum surfaces, are freely rotated in the substrate plane, and show an ∼11% contraction with respect to the inter-planar spacing in the ordered (111) face. The disordered close-packed-hexagonal structure seems to be the stable high-temperature surface phase of platinum.
Viscosity of Several Liquid Hydrocarbons as a Function of Temperature, Pressure, and Free Volume
Authors: Hogenboom David L. , Webb Wayne , Dixon Joseph A. 
Published: January 2005

Viscosity measurements have been made on nine pure hydrocarbon liquids at six temperatures ranging from 15.56° to 135°C and at pressures as high as 4000 bars. The samples included rigid bicyclic compounds of relatively high symmetry and three n-alkanes, n-C12, n-C15, and n-C18. These data were analyzed using the Eyring significant-structure theory, the Cohen—Turnbull free-volume model, and the empirical Doolittle equations. All of these equations produced essentially identical fits to the data at atmospheric pressure. The hypothesis that the constants v0 and vs in these equations represent the specific volume of a ``solid'' or condensed phase was tested by comparing best-fit values of these constants with experimental values for the solid-phase specific volume.
The Cohen—Turnbull and Doolittle equations were modified for use at elevated pressures with the result that the values of v0 necessary to satisfy the equations at high pressures were shown to be analogous to the specific volumes of a glassy state at high pressures. Further, the change in v0 as a function of pressure was compared with the change in the experimental values of the solid-phase volume at the melting point as a function of pressure and a definite correlation between the two was established.
Kinetics of Positive-Charge and Electron Scavenging and the Kinetics of Charge Neutralization in the Radiolysis of Dielectric Liquids
Authors: Freeman Gordon R. 
Published: January 2005

The kinetics of the scavenging of positive and negative species in spurs during the radiolysis of liquids is described. The motions of the positive ions, the solvated electrons, and the scavenger molecules are simultaneously taken into consideration. The kinetic equation contains two adjustable parameters, β and f, but in most instances f is taken as unity. The theory is tested, with moderate success, against previously published results of studies of positive-ion and electron scavenging in cyclohexane and n-hexane.
The recently observed complexity of the kinetics of ion-neutralization reactions in liquid cyclohexane, after a pulse of radiation, is explained in terms of the same model as that used in the scavenging kinetics.
It is concluded from the over-all success of the theory that solvated electrons form in suitable nonpolar molecular liquids, such as alkanes, during radiolysis.
The terms ``thermal electron'' and ``spur'' are not used by all authors to mean the same things, so they are discussed in the Appendixes in the hope that the meanings of these terms will become more standardized. The quasifree, trapped, and solvated states of electrons are distinguished in Appendix A. A definition of the term ``spur'' is offered in Appendix B.
Molecular Charge Distributions and Chemical Binding
Authors: Bader R. F. W. , Henneker W. H. , Cade Paul E. 
Published: January 2005

This paper presents an interpretation of the chemical binding found in the first-row homonuclear diatomic molecules. The interpretation is based upon the one-electron density distribution and the forces which it exerts on the nuclei. The general topographical features of the density distributions are discussed in relation to ``molecular size'' and the manner in which the total charge is partitioned between different spatial regions. The binding in these molecules is discussed in terms of the density difference distributions which picture the redistribution of charge which results from the formation of the molecule. It is proposed that the density difference distribution, or Δρ map, may be taken as the pictorial representation of the ``bond density.'' The forces exerted on the nuclei in the molecule are related to the changes in the charge distribution pictured in the ``bond density'' and a quantitative discussion of the manner in which electrostatic equilibrium is attained to give a stable molecule is given in terms of the forces. The concepts of bonding and antibonding are compared with the terms binding and antibinding, terms which are defined in terms of the forces exerted on the nuclei. In particular, both vertical and adiabatic ionization processes are viewed from the standpoint of the change in the electronic force contribution between the molecule and the molecule ion.
A definition of ionic and covalent binding based on the density difference distributions is presented. The Δρ map (or bond density) for covalent binding is shown to be characterized by a density increase located between the nuclei and shared equally by each. The Δρ map for ionic binding exhibits an increase in charge density which is localized on a single nucleus. A partitioning of the total electronic force in accordance with the Δρ maps demonstrates that in covalent binding, the nuclei are bound by the density which is shared between them, while in ionic binding the nuclei are bound by the density which is localized on a single nucleus.
Singlet—Triplet Transitions in p-Dihalogenated Benzenes
Authors: Castro George , Hochstrasser Robin M. 
Published: January 2005

The polarized absorption and also some emission spectra of single crystals of p-dichlorobenzene (DCB) and p-dibromobenzene (DBB) at 4.2°K are presented and vibrationally analyzed. The absorption to the lowest triplet states (T1) is sharp and displays a pure exciton origin in both crystals; at 27 890 cm−1 in DCB, and at 27 910 cm−1 in DBB. The assignment of these origins is confirmed by emission at 4.2°K. Modes belonging to species ag (all but one of the possible six are observed), b2g, b3g, b1u, b3u, and au are observed in the spectra, and the polarizations of the individual vibronic bands are presented. The bulk of the transition is polarized normal to the molecular plane. The identification of long-axis polarization in the 0, 0 band and normal polarization in a b2g vibronic level suggests an assignment 3B2u for the spatial character of the lowest triplet states.
The T1→S0 emission of DBB is very sharp and consists of an alternating intensity pattern in a long (∼20) sequence of the 278 b2g ground-state mode. From the analysis we conclude that the state T1 is slightly distorted into a trans chair form, and that the upper state contains a double minimum along this mode.
Crystal-field effects on the spectra T1←S0 are discussed in relation to lattice structure—which is prominent in the spectrum of DBB but not DCB—and in relation to the polarization ratios, and intermolecular spin—orbit coupling. The origin bands of DBB and DCB consist of triplets at about 0, 0+4.3, and 0+10.3 cm−1 and some possible reasons for this are discussed. The temperature dependence of the 0, 0 band of DBB is attributed to a subtle change in crystal structure with temperature.
For completeness the S1←S0 spectra were also examined, and a comparison is made of the vibrational frequencies in the states S0, S1, and T1.
The mechanisms of spin—orbit coupling in dihalobenzenes is examined in detail with reference to the symmetry and polarization assignments. Also a brief theoretical justification for the appearance of u-vibrational modes in the transition is given.