bluuebunny/crossref_metadata_2025 huggingface dataset:
Rate constants and vibrational energy disposal for reaction of H atoms with Br2, SF5Br, PBr3, SF5, and SF4
Authors: Malins R. J. , Setser D. W.
Published: February 2003

Rate constants and initial HBr and HF product distributions for the title reactions were measured in a fast-flow apparatus using infrared chemiluminescence techniques. The spectra were interpreted using a new set of Einstein coefficients for HBr, which are listed in the Appendix. The rate constants for HBr(v⩾1) and HF(v⩾1) formation, relative to the H+Cl2 reaction, are 3.3, 0.39, 0.50, 3.4, and 0.003, for Br2, SF5Br, PBr3, SF5, and SF4, respectively. This directly measured Br2 rate constant supports the smaller values that have been estimated in the literature. The initial HBr vibrational distribution (v1:v2:v3:v4:v5=0.03:0.20:0.40:0.31:0.06) from H+Br2 corresponds to 〈fV〉=0.49. The observed HBr vibrational distributions (v1:v2:v3:v4) are 0.28:0.43:0.23:0.06 and 0.63:0.24:0.13 for SF5Br and PBr3, respectively. The SF5Br results are close to the initial distribution and give 〈fV〉=0.36. The low vapor pressure of PBr3 limited the [PBr3] and high [H] was required to observe HBr emission; correcting the observed distribution for vibrational relaxation gives 〈fV≅0.47. These 〈fV〉 values include estimates for HBr(v=0). Based upon the highest HBr level observed from SF5Br and PBr3, D0(Br–SF5)<55 and D0(Br–PBr2)<62 kcal mole−1. The HF vibrational distributions from SF5 and SF4 decline with increasing v, which suggests that these reactions proceed via a long-lived complex. For these cases the formation of HF(v=0) is important, and significant corrections must be made to the HF(v⩾1) formation constants to obtain the total HF formation rate constants. The rate constants and energy disposal data are used to discuss models and to compare the H+Br2 reaction to H+Cl2 and F2.
Associative ionization of uranium atoms and oxygen molecules
Authors: Halle Jeffrey C. , Lo H. H. , Fite W. L.
Published: February 2003

The absolute cross section for the reaction U+O2→UO2++e has been remeasured in an experiment where a beam of U atoms from a tungsten oven passes through O2 gas at low pressure, and ions formed by the reaction are collected at one of two condenser plates on either side of the beam. Uranium atom density was determined from the time-integrated uranium atom current, which was determined by terminating the beam in a plastic bag, the uranium mass contents of which were measured by neutron activation analysis. The finding is that the effective cross section for a beam-through-gas experiment is 4.01 (±0.55)×10−17 cm2, a factor of 2.39 higher than the value determined in an earlier experiment of Fite, Lo, and Irving, where the time-integrated uranium atom current was measured by condensing the uranium on a plate and alpha particle counting of the condensate.
Molecular electronic property density functions: The nuclear magnetic shielding density
Authors: Jameson Cynthia J. , Buckingham A. D.
Published: February 2003

The general concept of a density function for a molecular electronic property is considered. The origin dependence of some electric and magnetic property densities is investigated and the nuclear magnetic shielding density function is used as a typical example. Density difference maps which reflect the changes in this electronic property upon molecule formation and bond extension are shown for the HF molecule and the related systems, the H atom and F− ion.
On the dissociation of doubly charged cations: (Mg–H2O)2+ and [Mg–(H2O)2]2+
Authors: Blake I. Ortega , Leś A. , del Conde P. G.
Published: February 2003

A b initio calculation were performed on the systems (Mg–H2O)2+ and [Mg–(H2O)2]2+. We looked into the possible dissociation processes of the two systems and found that (a) (Mg–H2O)2+ dissociates to Mg+ and H2O+, and (b) [Mg–(H2O)2]2+ dissociates to (Mg–H2O)2+ and H2O. The interaction energy curves of both systems are also presented. The relevance of these findings in relation to the behavior of doubly charged ion–ligand systems is discussed.
Quasiclassical trajectory calculations and quantal wave packet calculations for vibrational energy transfer at energies above the dissociation threshold
Authors: Gray Joni C. , Fraser Gerald A. , Truhlar Donald G. , Kulander Kenneth C.
Published: February 2003

Quantal wave packet calculations and quasiclassical trajectory calculations are reported for vibrational energy transfer and dissociation in collinear atom–diatom collisions. The system considered has the masses of H+H2 and is modelled with an extended LEPS potential energy surface. The conditions considered are initial vibrational states n1=0,1, and 4 and initial relative translational energies up to 12 eV for the wave packet calculations and up to 13 eV for the trajectory calculations. This is higher in energy than previous comparisons of quantal and trajectory calculations. The quantal transition probabilities show higher thresholds than the trajectory ones, and then they oscillate about the trajectory results. The first and second moments of the final vibrational action are similar for both kinds of calculation.
Calculation of multiplet structures in shakeup spectra by the Xα method
Authors: Tse John S.
Published: February 2003

The energy expression for calculating upper and lower states of shakeup lines in core line photoelectron spectra were derived. Using the SCF–Xα–SW approximation, we have obtained satisfactory results in molecules with strong hole–valence coupling. The results also suggested configuration interaction is important for molecules with low lying excited states.
Equations of state for liquids from the zero-temperature isotherm: Quantum corrections for hydrogen
Authors: Rosenfeld Yaakov
Published: February 2003

The Kerley ad hoc model for fluids and the variational hard sphere method are used to calculate the equation of state for the inverse power potentials and the Lennard-Jones system. Comparison of these results with the available computer simulation data enables us to assess the validity of the models considered. An extension of the Kerley model that enables to calculate quantum corrections to the equation of state for fluids from the Debye temperature of the solid is applied for hydrogen and deuterium with favorable results.
Dielectric relaxation studies. II. Phenolic Mannich bases in dilute solution
Authors: Jeyaraj M. , Sobhanadri J.
Published: February 2003

The dielectric relaxation processes in phenolic Mannich bases have been investigated by measuring the dielectric permittivity and loss in dilute solutions of benzene at three different microwave frequencies at 30°, 45°, and 60 °C. Results are analyzed in terms of Cole–Cole arc plots and two distinct relaxation times. The results establish the intramolecular hydrogen bonding of the –OH group. The overall molecular relaxation appears to be the predominant mechanism in these substituted phenols. Activation parameters have been calculated assuming dielectric relaxation to be an Eyring-type rate process.
On Gibbs phase rule for optical enantiomers
Authors: Wheeler John C.
Published: February 2003

Exceptions to the usual statement of Gibbs phase rule can occur in systems containing pairs of optical enantiomers or other special symmetries. We examine a modification of the phase rule proposed by Scott and its application to examples in two classes of purported exceptions. For the first class of examples we argue that the usual statement of Gibbs phase rule is in accord with the expected behavior of the system, while for the second we agree that a modification of the rule is required. We obtain a modified rule which gives conventional result when applied to the first class and a modified result in agreement with Scott’s, when applied to the second. In the second class of examples the phase diagram in terms of fields or intensities exhibits more phases meeting at a point or more degrees of freedom for a given number of phases meeting at a point than would be predicted by the usual phase rule. These occur when the P-phase coexistence set is of dimension less than P-1 because of the symmetries present. Even in these cases surface free energy effects favor, in the absence of external bias from the container walls, the reduction of the number of phases to that predicted by the usual Gibbs phase rule. Control of macroscopic variables such as energy, volume, and composition will not prevent such reductions from occurring, although their tendency to occur is a surface effect and the rates may be very low. External bias through special preparation of container walls may be sufficient to overcome this tendency and stabilize the larger number of phases.
Neutron diffraction studies of Ce0.33U0.67C2 and Ce0.67U0.33C2 at 296–4 °K
Authors: Atoji Masao
Published: February 2003

Neutron diffraction measurements have shown that in the ternary CeC2-type compounds, Ce0.33U0.67C2 and Cs0.67U0.33C2, the cubic NaCl-type structure, which is usually stable above about 1000 °C, can be arrested down to 4 °K due to a large strain energy of the disordered lattice. Also retained down to 4 °K are a random distribution of Ce and U atoms, as well as the orientational disordering of C2 molecules. The lattice parameters at 296–4 °K indicate no valency change, such as Ce3+→Ce4+. Ce0.33U0.67C2 showed no magnetic ordering at 296–4 °K in 0–21 kOe. Ce0.67U0.33C2 becomes a weak ferromagnet below 17 °K in 21 kOe, with the moment direction parallel to the [111] direction.
Structure and magnetic studies of bis-piperidinium tetrachlorocuprate
Authors: Drumheller John E. , Seifert P. L. , Zaspel C. E. , Snively Leslie O. , Emerson Kenneth
Published: February 2003

X-ray, magnetic susceptibility, and epr investigations of bis-piperidinium tetrachlorocuprate (C5H10NH2)2CuCl4 indicate that it is a complicated structure of CuCl4= chains and ribbons separated by piperidinium groups and that it exhibits weak antiferromagnetism with J/k approximately −0.8 °K. The space group is Pc and the unit cell data are a=8.218 Å, b=16.924 Å, c=12.186 Å, and β=100.5°. The possibilities of magnetic dimensionality transitions and disordering as a function of temperature are discussed.
Study on the triplet state of tetramethyl-p-phenylenediamine by microwave induced delayed phosphorescence
Authors: Matsui Kazunori , Morita Hiroshi , Nishi Nobuyuki , Kinoshita Minoru , Nagakura Saburo
Published: February 2003

The phosphorescent state of N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD) has been examined at low temperatures. The phosphorescence spectrum of TMPD in octane at 4.2 K consists of several broad bands with the 0,0 band around 440 nm. The relative radiative activities of the three spin sublevels for these bands determined by microwave induced delayed phosphorescence (MIDP) and the zero-field splitting pattern obtained by the MIDP and ESR magnetophotoselection methods have established the assignment of B2u for the orbital symmetry of the phosphorescent triplet state of TMPD. MO calculations of the T–T transition energy and intensity also support this assignment. The MIDP method has also been applied to the study of IR stimulated emission resulting from recombination of photoionized TMPD molecules with ejected electrons. The relative populating rates of the zero-field components in this case are found to be very different from those determined by usual intersystem crossing.
The vibrational factor group splittings in crystalline aniline
Authors: Tripathi G. N. R.
Published: February 2003

Evidence for intermolecular dynamic coupling in the molecular vibrations of crystalline aniline has been obtained for the first time. The Raman intensity patterns in polycrytalline aniline at 77 K and the infrared polarization in the oriented aniline films at 40 K are investigated. The crystal spectra are interpreted to deduce the probable site (C1) and factor group (D2h). Some of the earlier vibrational assignments are revised.
Low-frequency vibrational spectra and ring-puckering potential energy function of 3-phospholene and 3-phospholene-1-d1
Authors: Richardson L. W. , Jagodzinski P. W. , Harthcock M. A. , Laane J.
Published: February 2003

3-phospholene, CH2CH=CHCH2PH, and 3-phospholene-1-d1, CH2CH=CHCH2PD, have been synthesized and their vapor-phase infrared and Raman spectra recorded. Seven far-infrared transitions associated with the ring-puckering vibration were observed for each molecule; several low-frequency Raman lines coincident with the infrared bands were also detected. The kinetic energy functions with no artificial modifications were calculated for the two molecules. Using these and the spectroscopic data the same potential energy function was determined for both isotopic species. The asymmetric function has a single minimum corresponding to the endo configuration with the double-bond and the P–H group pointing in the same direction. The planar ring structure lies 331 cm−1 (0.95 kcal/mole) higher in energy and the similiar exo configuration is 785 cm−1 (2.24 kcal/mole) less stable. In addition to the pure ring-puckering transitions two weaker puckering sequences, originating from ring-twisting and P–H inversion excited states, and two sequences of hot bands and difference bands involving the P–H inversion excited states were also observed. From these a detailed energy map of the low frequency energy states was determined. The frequency shifts in the excited state of the P–H inversion demonstrate that this mode has a relatively strong interaction with the ring-puckering.
EPR studies of Rh and Rh(II) centers stabilized in NH4Cl single crystals
Authors: Sastry M. D. , Savitri K. , Joshi B. D.
Published: February 2003

The electron paramagnetic resonance (EPR) studies of gamma irradiated ammonium chloride single crystals doped with rhodium have given evidence to suggest the stabilization of Rh0 and Rh(II) at interstitial sites in a compressed octahedral coordination with D4h symmetry. The EPR spectrum of Rh0 has been found to be highly temperature dependent, the intensity increasing with the lowering of temperature and was observable only below −100 °C. Well resolved hyperfine structure due to 103Rh has been observed for Rh0 center. Its g values suggest that the unpaired electron is in a pure ‖3z2−r2〉 orbital, in contrast to the ‖x2−y2〉 character of the unpaired electron of Rh(II) center. At 77 °K superhyperfine structure due to four equivalent chlorines was observed in the EPR spectrum of Rh(II) center, indicating the overlap of ‖x2−y2〉 orbital with the equatorial ligands.
Inhomogeneous broadening of vibrational linewidths in polyatomic liquids
Authors: George S. M. , Auweter H. , Harris C. B.
Published: February 2003

The first account of inhomogeneous broadening of vibrational linewidths in non-hydrogen-bonded liquids is presented based on the combined results of isotropic spontaneous Raman studies and picosecond coherent probing experiments. The symmetric CH3-stretching vibrational linewidths studied were found to be inhomogeneously broadened to various degrees. A correlation between the inhomogeneous broadening and the liquid’s local number density distribution width is demonstrated, upon which a theoretical model for inhomogeneous broadening is developed. A stochastic line shape theory is constructed in which homogeneous and inhomogeneous broadening are treated simultaneously in terms of one vibrational correlation function. This treatment unifies the fast and slow modulation approaches to vibrational dephasing and demonstrates how isotropic spontaneous Raman scattering studies and picosecond coherent probing experiments can be used in conjunction to study the inhomogeneous broadening of vibrational linewidths.
Radiative transition probabilities, lifetimes, and dipole moments for all vibrational levels in the X 1Σ+ state of 7LiH
Authors: Zemke Warren T. , Stwalley William C.
Published: February 2003

The recently reported [J. Chem. Phys. 66, 5412, 67, 4785 (1977)] hybrid potential curve for the X 1Σ+ state of LiH is combined with the ab initio dipole moment function of Docken and Hinze [J. Chem. Phys. 57, 4936 (1972)] to calculate radiative transition probabilities between all (v=0–23) vibrational levels of the X 1Σ+ ground state of 7LiH. In addition, the spontaneous emission lifetimes for all the vibrational–rotational levels with J=0, 1, and 10 are given, as are the dipole moments for all vibrational levels (J=0).
Radiative and nonradiative decay rates of state selected H–(C≡C)–2H+, D–(C≡C)–2D+, Ã2Πu, determined by a photoelectron–photon coincidence technique
Authors: Maier John P. , Thommen Fritz
Published: February 2003

Fluorescence quantum yields and cascade-free lifetimes of diacetylene and dideuterodiacetylene cations in selected vibrational levels in the Ã 2Πu state have been measured. This was accomplished by the detection of coincidences between energy selected electrons and undispersed photons following ionization by He(Iα) photons. The radiative and nonradiative rate constants of such state selected cations under collision-free conditions are therefore directly obtained. The fluorescence quantum yields are high, but not unity, and decrease as do the lifetimes on increasing the internal energy in the Ã 2Πu state. These first results are used to illustrate the decay behavior of open-shell organic cations for which only the 2Ã→ 2X̃ internal conversion process completes with the 2Ã→ 2X̃ radiative relaxation.
The application of an effective nuclear charge model to the prediction of valence force constants in tetrahedral XY4 molecules. III
Authors: Ohwada Ken
Published: February 2003

With the use of effective nuclear charges defined from the quadratic force constants of homonuclear diatomic molecules, calculations of valence force constants for tetrahedral XY4 molecules are carried out illustrating the effective nuclear charge model previously developed. The calculated results are compared with the experimental force constants which are determined by the normal coordinate analysis. The agreement between the calculated and experimental force constants is moderately good for most molecules under investigation. This suggests that the effective nuclear charge model is useful for the prediction of approximate valence force constants in more complicated polyatomic molecules.
Laser induced multiphoton ionization mass spectrum of benzene
Authors: Reilly James P. , Kompa Karl L.
Published: February 2003

Gas phase benzene is multiphoton ionized under low pressure, collision-free conditions in the source region of a time of flight mass spectrometer using UV excimer laser radiation. All of the ions generated are identifiable and derive from C6H6. The differences between KrF and ArF laser induced mass spectra and total ionization yields are interpreted on the basis of known fragment ion appearance potentials, and a rate equations model which describes the ionization process. The observed mass spectra exhibit certain characteristics not found in conventional electron impact spectra. These idiosyncracies may enhance its potential as a mass spectrometric ionization source.
Temperature dependence of Mg porphin, Cu porphin, and Pd porphin luminescence
Authors: Bohandy Joseph , Kim Boris F.
Published: February 2003

Fluorescence spectra of MgP in triphenylene and phosphorescence spectra of CuP and PdP in triphenylene have been obtained from room temperature down to 10 °K. Analysis of the temperature dependence of the MgP spectra shows that the coupling between the Mg porphin guest and the triphenylene host is weak. A temperature-dependent splitting of the 0–0 phosphorescence band of PdP, previously observed in nonane, was also observed in triphenylene but our attempt to verify a suggested explanation was inconclusive. For CuP in triphenylene, a TD–TQ separation of 267 cm−1 has been measured.
Anomalous hyperfine interactions in FeOCl intercalation compounds: The van der Waals layer lattice modes
Authors: Herber R. H. , Rein Alan J.
Published: February 2003

The vibrational states of FeOCl are studied from observations of the far-infrared absorption spectra.(AIP)
ESR–ENDOR study of radiation effects in zinc acetate
Authors: LoBrutto Russell , Budzinski Edwin E. , Box Harold C.
Published: February 2003

Primary radiation products in X-irradiated zinc acetate are investigated. The ESR absorption spectra from single crystal of zinc acetate is reported ENDOR measurements are also reported. (AIP)
On the determination from Raman spectra of the polarizability derivative with respect to the O–D bond stretching coordinate in the ices
Authors: Bertie John E. , Francis Bernard F. , Scherer James R.
Published: February 2003

Several different measurements 1,2,3,4 of the integral intensities in the Raman spectra of polycrystalline ice are discussed. The polarization derivatives derived from the intensity measurements are compared. (AIP)
Multiphoton dissociation of ethyl chloride at 3.3 μm: Excitation mechanism and rate equations analysis
Authors: Dai Hai-Lung , Kung A. H. , Moore C. Bradley
Published: February 2003

Tunable 3.3 μm laser pulses were used to excite the CH stretching modes of ethyl chloride. Energy deposition vs fluence was measured optoacoustically. For 3.3 μm excitation, absorbed energy increases almost linearly with fluence, while for 10 μm excitation there is substantial saturation. Dissociation yields were measured as a function of fluence and of wavelength by gas chromatographic determination of C2H4 from C2H5Cl+nhν→C2H4+HCl. Much higher yields were observed for 3.3 μm excitation than for CO2 laser 10 μm excitation. Sharp resonances in the 3.3 μm dissociation yield spectrum match peaks in the fundamental and overtone absorption spectra. Overtone spectra show that for many rotational states the vCH=2 level (6000 cm−1) is in the quasicontinuum and that vCH=3 is always in the quasicontinuum. The resonant nature of the excitation allows the rate equations description for transitions in the quasicontinuum and continuum to be extended to the discrete levels. Absorption cross sections are estimated from ordinary IR spectra. A set of cross sections which is constant or slowly decreasing with increasing vibrational excitation gives good fits to both absorption and dissociation yield data. The much smaller dissociation yields and the saturated absorption at 10 μm reflect bottlenecking in the discrete levels. As ethyl chloride pressure is increased from 0.2 to 2 Torr the fraction dissociated decreases by nearly a factor of 2. Only about 10% further decrease occurs from 2 to 6 Torr. The rate equations model gives a similar curve when the strong collision assumption is made for vibrational relaxation and RRKM dissociation rates are used.
Repulsive forces of simple molecules and mixtures at high density and temperature
Authors: Ross M. , Ree F. H.
Published: February 2003

Shock wave data for liquid Ar, Xe, N2, O2, CO2, CH4, and CO have been used to test the possibility that the repulsive pair potential of these fluids scale in accordance with the ’’Law of Corresponding States.’’ This is found to be approximately valid to a compression of about 2.5 times liquid density. The law has been applied to compressed mixtures of N2 and O2 and a theoretical prediction of the detonation velocity and pressure of liquid NO is found to be in excellent agreement with experiment.
Theoretical studies of H2–H2 collisions. II. Scattering and transport cross sections of hydrogen at low energies: Tests of a new a
b i
n
i
t
i
o vibrotor potential
Authors: Monchick Louis , Schaefer Joachim
Published: February 2003

Close-coupled calculations of scattering amplitudes have been carried out for H2–H2 collisions for a new ab initio potential energy surface, treating the hydrogen molecules as true vibrotors. The amplitudes were inserted into the kinetic theory expressions for integral and transport cross sections and used to compute (1) the elastic scattering of (j=0, v=0) para-hydrogen for relative velocities between 1000 and 2500 m/sec; (2) the viscosity differences of ortho- and para-hydrogen for temperatures less than 25 °K; and (3) the thermal diffusion ratio of ortho- and para-hydrogen for temperatures between 50 and 150 °K. The agreement with experiment is highly satisfactory and provides a thoroughgoing test of the new potential energy surface.
Dissociative ionization of N2O produced by 1 MeV H+, He+, O+ projectiles
Authors: Shah A. V. , Monce M. N. , Edwards A. K. , Steuer M. F. , Wood R. M.
Published: February 2003

N2O is bombarded with 1 MeV H+, He+, and O+ projectiles. The dissociation fragments observed are N+, O+, NO+, N2+, N2+, and O2+. Kinetic energy spectra of singly ionized fragments obtained using a time-energy spectroscopy TES technique are reported. The relative intensities and the absolute yields of these fragments are dependent on the type of projectile which is used to bombard the target gas. Bombardment with O+ projectiles produces the most absolute yield and enhances the yield of 5 to 10 eV fragments relative to the yield of 0 to 5 eV fragments. These spectra are interpreted and a comparison is made to electron impact and photoionization studies of N2O by other groups. This study indicates that the dissociation channels N2O2+→NO+ + N+ and N2O2+→ N2+ +O+ are probable major contributors to the yields of NO+ and N2+. In addition, the O+ and N+ spectra exhibit high energy tails which may be attributed to multibody break up.
Spin dependent properties of perturbed wave functions: An analytic comparison of the exact, UHF, and spin-projected UHF states
Authors: Rossky Peter J. , Karplus Martin
Published: February 2003

A generally applicable diagrammatic representation for spin-annihilated wave functions is developed; the diagrammatic approach avoids the complex algebra usually associated with the application of spin-annihilation operators. The diagrammatic formulation is first applied to the perturbation expansion for the exact wave function to elucidate the diagrammatic origin of the (correct) spin eigenfunction properties of the exact perturbed state. Employing a previously derived perturbation expansion for the unrestricted Hartree–Fock (UHF) wave function, the diagrammatic spin-annihilation formalism is then used to analyze the effect of projecting unwanted spin states from the UHF wave function. Results obtained for the projected UHF state are compared to those appropriate to both the exact perturbed wave function and the unprojected UHF wave function. It is shown that results obtained by annihilating only the lowest unwanted spin multiplicity are expected, in a perturbation theory sense, to be very similar to those obtained by annihilating all unwanted spin states. However, it is further shown that additional terms are introduced into the UHF wave function by the spin projection procedure and that these terms are in general unrelated to the exact perturbative corrections to the UHF state. In particular, the wave function, energy, one and two-electron density matrices, and spin densities obtained for the projected state are all shown to be in error in the lowest order of perturbation theory; in contrast, the UHF state leads to the correct one-electron density matrix and spin densities in lowest order.
Numerical evaluation of the porous medium effective diffusivity between the Knudsen and continuum limits
Authors: Ho Fun Gau , Strieder William
Published: February 2003

A variational principle based on the mean free path kinetic theory of gases is used to calculate the effective diffusion coefficient for gaseous diffusion through a bed of overlapping solid spheres for arbitrary Knudsen number and porosity φ. Effects of tortuosity of the diffusion paths are considered by including the flux around the solid spherical obstructions explicitly in the trial functions. Computer evaluations of the variational integrals are performed for Knudsen numbers from 0.1 to 100 and porosities from 0.01 to 0.99. The simple Bosanquet formula for series addition of the effective bulk and Knudsen diffusivities is compared with the variational calculations of the effective diffusivity. The Bosanquet formula is found to be exact for low porosities, and a suprisingly good approximation even at higher porosities. From the slopes at large Knudsen numbers, we propose a new variational expression for the Knudsen tortuosity τKn for a bed of overlapping spheres, τKn=9/8−(1/2) lnφ+(13/9−9/8)φ2/5.
Vaporization chemistry and thermodynamics of the lead–indium–sulfur system by computer-automated Knudsen and torsion effusion methods
Authors: Haque Reza , Gates Alfred S. , Edwards Jimmie G.
Published: February 2003

Vaporization of PbIn2S4(s) was studied by computer-automated simultaneous Knudsen and dynamic torsion effusion. Vapor pressures and the apparent molecular weight of the effusing vapor were displayed in real time. The vaporization reaction was PbIn2S4(s)=In2S3(s)+PbS(g). The vapor pressure was measured 108 times in the temperature range 948–1086 K. For the vaporization reaction, third-law analyses gave ΔH°(298 K)=253.0±0.1 kJ/mol. The enthalpy of PbIn2S4(s) with respect to its constituents PbS(s) and In2S3(s) was −23±4 kJ/mol. The apparent molecular weight showed stoichiometry changes in indium sulfide during the experiment. Residual indium sulfide, remaining after loss of all PbS, vaporized with some nonstoichiometry by In2S3(s)= In2S(g)+S2(g). The vapor pressure of the residual indium sulfide was measured 57 times in the temperature range 1035–1121 K;third-law analyses yielded ΔH°(298 K)=613.4±0.4 kJ/mol for the dissociative vaporization reaction. The compound Pb2In6S11(s), found at lower temperatures, had negligible stability at the temperatures of this investigation. The unit cell of PbIn2S4(s) was orthorhombic with a=2.275 nm, b=1.356 nm, and c=1.953 nm.
High pressure study of luminescence from intramolecular CT compounds
Authors: Rollinson A. M. , Drickamer H. G.
Published: February 2003

The effects of high pressure on the luminescence properties of four organic intramolecular charge transfer compounds were investigated. The compounds were studied in a wide range of liquid and polymeric environments, and for one of the compounds, the effect of chemical substitution was also examined. In general, an increase of pressure affects the luminescence in a way which is in some degree similar to an increase of solvent polarity. A single configuration coordinate model was used to interpret the luminescence in terms of excited state interactions. Three of the compounds exhibited only fluorescence: p-(9-anthryl)-dimethylaniline (ADMA), 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and 1-anilino-8-naphthalenesulfonate (ANS). Fluorescence from the first two compounds in nonpolar media is attributed to an excited state relatively unaffected by the charge transfer process. In polar media, fluorescence is believed to originate from another excited state that possesses considerable charge transfer character, and whose energy is strongly influenced by solvent polarity. At high pressure, an apparent fluorescence shift to higher energy was observed in viscous alcohols apparently due to the introduction of fluorescence from the energetically higher lying non-charge transfer excited state. This explanation is supported by the dual fluorescence decay observed from ADMA coincident with the sign reversal in fluorescence peak shift. Three excited states are believed to affect ANS fluorescence, two of them with charge transfer character. The model describing the excited states of ADMA and PRODAN is consistent with ANS fluorescence except in glycerol, whose anomalous behavior is discussed in the text. The fourth compound, nitroaniline, was studied in its three isomeric forms, with and without N-methylation. In addition to affecting the phosphorescence and fluorescence of p-nitroaniline, pressure studies indicate that nπ* singlet and triplet states figure prominently in the radiative and nonradiative processes of o-nitroaniline and m-nitroaniline as well.
Dititanium and divanadium
Authors: Cossé C. , Fouassier M. , Mejean T. , Tranquille M. , DiLella D. P. , Moskovits M.
Published: February 2003

The Ar+ laser-excited spectrum of matrix-isolated V2 consists of a resonance Raman progression with ωe=537.5 cm−1 and ωexe=4.2 cm−1. With increasing laser power several members of an anti-Stokes progression and sequence components on both Stokes and anti-Stokes members of this progression were observed and attributed to transitions originating from vibrationally excited stated populated as a result of laser irradiation. A second system with ωe=508 and ωexe=3.3 cm−1 also grew in with increasing laser power and 496.5 nm excitation. This was interpreted as a resonance Raman progression within an electronically excited state (A) of V2. The electronic resonance Raman spectrum corresponding to the A→X transition was also observed as well as one to another low-lying electronic excited state. The v′=0 level of state A was found to lie 1860 cm−1 above the v″=0 level of the ground state. The multiple photon nature of the transitions discussed above was determined by performing laser power measurements. The resonance Raman spectrum of Ti2 was excited with HeNe and dye laser illumination in solid argon matrices containing titanium. As with V2, laser irradiation populated excited vibrational states of the ground state, producing an anti-stokes, resonance Raman progression. Isotopic components of Ti2 were resolvable under high resolution, corroborating the assignment. A discussion of multiple bonding in transition metal dimers is presented which shows that the contribution of bonds originating from the atomic d orbitals do not always contribute uniformly to the metal–metal force constant. Hence the formal bond order is not always a good gauge of the bond strength of a transition metal dimer.
Three-dimensional quantum mechanical studies of D+H2→HD+H reactive scattering. IV. Cross sections and rate constants with rotationally excited target molecules
Authors: Sun J. C. , Choi B. H. , Poe R. T. , Tang K. T.
Published: February 2003

The body fixed formulation of the adiabatic distorted wave theory is used to study the reactive collisions of the (D,H2) system. Cross sections are obtained on the ab initio potential surface from the threshold to 0.5 eV in relative translation energy for the case where the target molecule is in the first rotationally excited state. The present results of the ortho-hydrogen are qualitatively similar to but quantitatively different from the previous results of para-hydrogen. The statistically weighted cross sections and product state distributions are found in general agreement with the molecular beam experiment. The reaction rates are obtained by integration over the distribution function. From 150 to 750°K where there are experimental data, the curvature in the Arrhenius plot of the calculated rate constants is in excellent agreement with experiment. However, the absolute magnitudes of the rate constants are smaller than the experimental ones.
Intensities in pure rotational CARS of air
Authors: Roland C. M. , Steele W. A.
Published: February 2003

Measurements of the pure rotational CARS spectrum of N2 and O2 in air are reported. The spectrum was obtained using a three-color pulsed laser arrangement. Quantitative agreement between experiment and the calculated variations in intensity and line shape is obtained.
Picosecond kinetics of acridine in solution
Authors: Shapiro S. L. , Winn K. R.
Published: February 2003

The fluorescence lifetime of acridine depends upon the excitation and emission wavelengths in certain solvents. The lifetime is also a sensitive function of temperature and medium, and variations are interpreted in terms of the hydrogen bonding characteristics of the solvents.
Raman probing of excited states of the tris(2,2′-bipyridine)Cr(III) complex having lifetimes in the micro-and picosecond regions
Authors: Asano M. , Koningstein J. A. , Nicollin D.
Published: February 2003

Population and Raman scattering of the 2E and 4T2 electronic excited states with lifetimes of τE?60 μs and τT?10 ps of the complex tris(2,2′-bipyridine)Cr(III) is achieved by exposing the complex Cr(bpy)3 (ClO4)3 in H2O to radiation at 457.9 nm from tunable pulsed and cw fixed wavelength lasers. The spectra for 2E and ground state Cr(bpy)33+ are very similar but differences of intensities, FWHM and shifts of corresponding vibrational Raman bands of 4T2 and 4A2:Cr(bpy)3+ are more pronounced. The differences in FWHM are attributed to the contribution to the overall Raman intensity for the former of vibrational scattering in vibrational states in the top as well as in the bottom of the 4T2 electronic surface of some of the modes of the complex. This because the wavelength of the pumping source is in resonance with vibrational states in the top of that surface and the cascading process reveals itself in the time resolved Raman studies at the nanosecond level.
Proton coordinates in Er(C2H5SO4)3⋅9H2O and ErCL3⋅6H2O from single crystal NMR studies
Authors: Sato Setsuko , Reuveni Amikam , McGarvey Bruce R.
Published: February 2003

Proton coordinates have been determined for all hydrate protons in Er(C2H5SO4)3⋅9H2O and ErCl3⋅6H2O from NMR studies on single crystals. The paramagnetic NMR shift in these systems has been determined to be completely point dipolar within experimental error. In the case of Er(C2H5SO4)3⋅9H2O it was found that ’’jump rotation’’ or tunneling motion was occurring at −10 °C which averaged the NMR shift for the two water protons but left the dipolar interaction between the two protons intact. No such motion was observed for ErCl3⋅6H2O at room temperature. Methods of analysis of NMR in single crystals having rare earth ions have been developed which are capable of giving proton coordinates in a unit cell to an accuracy of 5 pm without the need of a very precise orientation of the crystal relative to the magnetic field.
Rate constant/diffusion coefficient ratio for electron reactions in the radiolysis of supercritical hydrocarbons
Authors: Nishikawa Masaru
Published: February 2003

The ratio of rate constant for electron reactions to the sum of the electron and hole diffusion coefficients is expressed in terms of the reactivity parameter on the basis of the solution of Smoluchowski equation obtained by Crumb and Baird and by Tachiya. Comparison of this expression with that obtained previously with the use of Nernst–Einstein relationship as to several types of distribution function suggests the Gaussian function is the best representation of the initial distribution of electrons in the radiolysis of supercritical hydrocarbons.
Homogeneous nucleation in associated vapors. III. Heptanoic, decanoic, and myristic acids
Authors: Agarwal Gopal , Heist Richard H.
Published: February 2003

Homogeneous nucleation measurements have been made on heptanoic, decanoic, and myristic acid vapors, all of which exhibit small degrees of hydrogen bond association. The measured temperature dependences of the critical supersaturation are compared with predictions of the Katz–Saltsburg–Reiss theory for nucleation in associated vapors as well as the conventional Becker–Döring–Zeldovitch theory. Heptanoic acid and decanoic acid show good agreement with theory while the myristic acid critical supersaturation measurements are consistently low.
Thermodynamic study of the molecules BiLi and PbLi by Knudsen effusion mass spectrometry
Authors: Neubert A. , Ihle H. R. , Gingerich K. A.
Published: February 2003

The composition of the gas phase over lithium alloys with bismuth and lead, respectively, has been investigated. Equilibria involving the molecules BiLi (g) and PbLi (g) have been studied using Knudsen effusion mass spectrometry. From the measured data and from auxiliary data from the literature the following dissociation energies, D00; and standard heats of formation, ΔHf,0, were obtained: D00(BiLi)=(135.7±6) kJ mol−1=(32.4±1.4) kcal mol−1, D00(PbLi)=(74.9±8 kJ mol−1=(17.9±1.9) kcal mol−1, ΔHf,00(BiLi (g))=(231.9±7) kJ mol−1=(55.4±1.7) kcal mol−1, and ΔHf,00(PbLi (g))=(278.6±9) kJ mol−1 =(66.6±2.2) kcal mol−1.
Self-diffusion of oxygen in single crystal alumina
Authors: Oishi Y. , Ando Ken , Kubota Y.
Published: February 2003

The self-diffusion coefficient of oxygen in (polished slices of a Verneuil) single-crystal alumina was determined in the temperature range 1500–1770 °C by means of the gas–solid isotope exchange technique. The results were represented by D=1.12×103 exp (−155×103/RT) cm2/s. The activation energy was interpreted to be for intrinsic diffusion. By comparison of the results with the oxygen self-diffusion coefficients previously reported for crushed particles of a Verneuil alumina and a vapor-grown alumina, the extrinsic diffusion exhibited by the crushed particles was confirmed to be due to a dislocation enhancement process.
Proof of the symmetry of the transport matrix for diffusion and heat flow in fluid systems
Authors: Sekerka R. F. , Mullins W. W.
Published: February 2003

A phenomenological proof is given of the symmetry of the transport matrix (Bij) of coefficients in the constitutive laws that describe mass and energy transport in a multicomponent fluid for the following choices of frame, forces, and fluxes: the local center of mass frame; the forces ∇(μi/T), where μ0=−1, T is the temperature, and μi for i=1,...K is the chemical potential of the ith component; and the fluxes ji, where j0 is the nonconvective internal energy flux and ji for i=1,...K is the mass flux of the ith component. The proof is based on Onsager’s reciprocity theory and proceeds by using the equations of hydrodynamics and the constitutive equations, postulated to describe mass and energy transport in the fluid, to calculate the time development of a specially selected fluctuation, when that fluctuation is considered to be macrovariation. The resulting dynamical equations are cast into the Onsager form by use of the generalized forces obtained from a thermodynamic calculation of the entropy change ΔS associated with the fluctuation; the principle of local equilibrium is used in the latter calculation. Our proof then follows by a demonstration that the symmetry of the matrix (Bij)is equivalent to the symmetry of the matrix (Lij) established by Onsager’s abstract proof. Special forms of the constitutive equations with symmetric coefficients are given for the case in which the dependence of the driving forces on temperature is isolated. Our proof is based on thermodynamics and phenomenological equations and is therefore independent of any particular statistical model; it does, however, agree with the conclusions of the statistical mechanical analysis of the fluid model studied by Kirkwood and Fitts and with a phenomenological analysis by Onsager for the special case of constant temperature and pressure.
Piezoelectric Cs2S2O6: Room temperature crystal structure
Authors: Liminga R. , Abrahams S. C. , Bernstein J. L.
Published: February 2003

Cesium dithionate, Cs2S2O6, is moderately strongly piezoelectric at room temperature and crystallizes in the hexagonal system with space group P63mc and two formula units in the unit cell. The lattice constants at 298 K are a=6.356 58±0.000 04 and c=11.539 07±0.000 04 Å (λCuKα1=1.5405 98 Å). The integrated intensities of most reflections with (sin ϑ)/λ?1.08 or 1.15 Å−1 were measured using two crystals and diffractometers. The first crystal gave a total of 1116 independent Fmeas, the second gave two separate sets of structure factors: 415 Fmeas with the crystal having received more radiation exposure than the first crystal and a further 431 Fmeas with still greater radiation exposure. The crystal structure was solved from the Patterson function and Fourier series and refined by the method of least squares. The final agreement factor R=0.033 for the first set, 0.049 and 0.060 for the second two sets of Fmeas. The crystal undergoes x-irradiation damage, with some reflections decreasing in integrated intensity by more than a factor of two. Normal probability plot analysis is used to compare the sets of Fmeas and resulting structural parameters. Redistribution of the Cs+ ions along the trigonal axes is likely, with compensating rearrangement of the S2O6−2 ions. The S2O6−2 ion has a staggered configuration close to 3̄m symmetry, with S–S=2.112±0.003, mean S–O=1.454±0.002 Å in length and S–S–O angle of 104.3±0.2 °, O–S–O=114.1±0.2 °. The two independent Cs+ ions are each nine-coordinated, with average Cs–O=3.231 Å. Layers with stoichiometric composition form normal to the polar axis.
Model networks of end-linked polydimethylsiloxane chains. IX. Gaussian, non-Gaussian, and ultimate properties of the trifunctional networks
Authors: Andrady A. L. , Llorente M. A. , Mark J. E.
Published: February 2003

Model elastomeric networks were prepared by end-linking hydroxyl-terminated polydimethylsiloxane chains with a trialkoxy silane. Mixtures of various proportions of relatively long and very short chains were employed, since the resulting ’’bimodal’’ networks are of unique importance in characterizing non-Gaussian effects related to limited chain extensibility. Stress–strain isotherms of these trifunctional networks gave values of the elongation at which the modulus begins to increase anomalously, and values of the elongation and modulus at the point of rupture. These results were interpreted in terms of calculated values of the maximum extensibilities of the chains, and were compared with previously reported results on the corresponding tetrafunctional networks in order to characterize the effects of crosslink functionality on these properties. In addition, the elasticity constants characterizing the Gaussian regions of the isotherms, and values of the degree of equilibrium swelling were used to evaluate the most recent molecular theories of rubberlike elasticity, particularly with regard to how the elastic effectiveness of the network chains depends on chain length and extent of deformation.
Investigations on a new series of organic conductors: The tetraselenotetracene iodides (TSeT-Ix)
Authors: Delhaes P. , Coulon C. , Flandrois S. , Hilti B. , Mayer C. W. , Rihs G. , Rivory J.
Published: February 2003

A new series of radical-cation salts, the tetraselenotetracene iodides TSeT-Ix, have been synthesized by a cosublimation process. Three different stoichiometries have been obtained on which the structural and physical properties have been investigated. Phases B and C, TSeT-I0, 71 and TSeT-I0, 77, respectively, are semiconducting materials with incommensurate iodine sublattices; phase B exhibits a strong hysteresis effect detected by dc electrical conductivity and EPR linewidth measurements. The existence of elastic microdomains is postulated to explain this behavior. Concerning phase A, which is an ordered structure (TSeT-I0,5) we show that it is a molecular metal (the quality of which is sensitive to the preparation conditions). By using a general diagrammatic representation we are able to compare this salt to other one-chain compounds. We conclude that systems, the conductivity of which is dominated by radical cation chains, are organic metals potentially as good as charge transfer complexes belonging to TTF TCNQ series.