bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of effective polarizabilities from electro-optical experiments using microscopic and macroscopic theories of the local electric field
Authors: Burnham A. K. , Gierke T. D.
Published: February 2003

Previous theoretical results are summarized in which the microscopic fluctuation theory of Ladanyi and Keyes was extended to include the optical Kerr effect (OKE), Cotton–Mouton effect (CME), and light scattering (LS) intensities from liquids composed of asymmetric molecules. Data from the literature for these experiments is compiled and evaluated, and a comparison is made between theory and experimental results for molecules with axial and C2v symmetry. CME, OKE, and depolarized LS results are combined with harmonic generation results to obtain an estimate of the orientational pair correlations in liquids. Good agreement is found with previous determinations from dilution experiments. The results obtained from the microscopic treatment are shown to be of the same functional form as the macroscopic ellipsoidal Lorentz theory. A comparison of the results from the two theories allows a detailed examination of the microscopic approximations in the macroscopic theory. Expressions are obtained for ’’effective’’ molecular polarizabilities and hyperpolarizabilities in terms of gas phase values and cavity anisotropies.
Rotational spectrum and structure of KCN
Authors: Törring T. , Bekooy J. P. , Meerts W. Leo , Hoeft J. , Tiemann E. , Dymanus A.
Published: February 2003

The spectrum of gaseous KCN was measured in the frequency range between 2 and 39 GHz by microwave absorption and by molecular-beam electric-resonance spectroscopy. Combination of the new results with earlier microwave data of KCN in the 100 GHz range made it possible to assign 64 transitions to the ground vibrational state and to fit them to the asymmetric rotor model. The three rotational constants, the five quartic distortion constants, and two sextic distortion coefficients could be determined. Assuming a CN distance of 1.162(10) Å we find rKC=2.6(1) Å and uKCN=76 °(10). The molecules thus have a nonlinear, T-shaped structure. The inertial defect gives an estimated value of the lowest vibrational frequency of KCN ω2=157 cm−1, which is in reasonable agreement with ω2=139 cm−1 from matrix-isolation studies.
Transfer and storage of vibrational energy in liquids: Liquid nitrogen and its solutions with carbon monoxide
Authors: Chandler David W. , Ewing George E.
Published: February 2003

We have produced vibrational excitation in liquid nitrogen and its solutions with carbon monoxide by flooding the samples with infrared radiation from a blackbody source. Infrared fluorescence from these excited liquids was monitored in order to investigate their relaxation kinetics and spectral profiles. For the first time the collision induced emission of excited liquid nitrogen is reported. The radiative decay of undoped nitrogen, which is a measure of the ability of the liquid to store vibrational energy, was measured to be 45±5 sec; however, fluorescence could be detected for over 2 min. New relaxation channels are opened for excited N2 when CO is added and the lifetimes are shorter. These relaxation channels were investigated in detail. The radiative lifetime of excited CO in liquid nitrogen was determined. We were also able to place upper limits on the V–T,R relaxation rates of excited CO and N2 in the liquid. In addition to these rate constants, a model for radiation trapping was developed which successfully mimicked the observed kinetic and spectral behavior of the liquid N2–CO system in the region where self-absorption dominates.
Laser-induced fluorescence of NaK and the dissociated atoms
Authors: Katô Hajime , Noda Chifuru
Published: February 2003

Intensity distribution of both bound–bound and bound–continuum transitions of the NaK d 3Π1→a 3Σ+ fluorescence has been analyzed by calculating Franck–Condon factors for the transitions. The potential curves of the d 3Π1 state and the dissociative continuum of the a 3Σ+ state have been estimated by comparing the observed and the calculated intensities, and the variation of the transition dipole moment with internuclear distance has been evaluated. Besides molecular fluorescence, the fluorescence of the D lines of Na and K atoms were observed. The absolute and the relative intensities of the atomic D1 and D2 lines have been found to be different between the Na and K atoms. The effects of a foreign gas on atomic D lines and their dependence on a frequency of excitation are studied, and the mechanism responsible for the atomic emission is examined.
A theoretical treatment of the time dependent Kerr effect following a sudden change of a homogeneous electric field of arbitrary strength
Authors: Watanabe Hiroshi , Morita Akio
Published: February 2003

The theoretical treatment of the transient Kerr effect in the previous paper is extended to the case where a homogeneous electric field is suddenly applied to a system in which a Boltzmann distribution of molecular orientation has been established by another homogeneous electric field. An equation which has a convenient form for computer calculation is proposed. Accuracy of the numerical results of the equation is examined and compared with other theories. It is shown how the transients for reversing pulses depend on the field strength and on the ratio of the induced dipole moment to the permanent dipole moment in a molecule at moderate field strengthes. The dependence of the relaxation time of rise process on the field strength is also examined in comparison with our previous theoretical expressions.
Adsorption of O2 and N2O on carbon-covered Ru(001) surfaces
Authors: Shi S.-K. , White J. M.
Published: February 2003

The dissociative chemisorption of N2O and O2 on carbon-covered Ru(001) surfaces has been studied by Auger electron spectroscopy. Small amounts of carbon sharply lower the dissociative probability for N2O as compared to O2. Carbon blocks sites for atomic oxygen adsorption and one monolayer of carbon removes the dissociation activity for O2 and N2O. The results are interpreted in terms of a significant effect of carbon on the N2O molecular precursor state and in terms of more restrictive surface site requirements for N2O as compared to O2.
Thermal instability in a plastic crystal
Authors: Terauchi H. , Maeda H. , Kamijo N.
Published: February 2003

X-ray diffuse scattering from hexamethyletane (HME) is carefully examined to investigate the acoustic instability near the plastic–solid phase transition temperature Tc=159 K. It is found that the elastic constant C44 becomes vanishingly small just above Tc.
On the interpretation of adsorption bond lengths from LEED crystallography
Authors: Mitchell K. A. R.
Published: February 2003

Surface bond lengths from LEED crystallography have mainly been related to sums of ’’hard-sphere’’ radii, although a recent analysis [Mitchell, Surf. Sci. (in press)] attempted to relate more closely to covalent bonding concepts, particularly those developed by Pauling. This framework is now applied to the adsorption bond lengths determined by LEED for three new systems: Ir(111)–(2×2)–0, Al(111)–(1×1)–0 and Ir(111)–(√3×√3)30°–S. Discussions are also given for Pd(100)–c(4×2)45°–CO and Ni(100)–(2×2)–C, although at present there is only very limited data for comparing with these two additional surface structures.
Vibrations of potassium and cesium thiocyanates crystals. V. Internal modes
Authors: Ti S. S. , Ra O/.
Published: February 2003

A dynamical calculation on the internal vibrations is reported for the orthorhombic crystals of potassium and cesium thiocyanates. The modes frequencies based on several force fields are computed and observed to show considerable dispersion when the wave vector differs from zero. The modes behavior of the internal vibrations is also discussed.
On equation of state calculations from experimental zero-temperature isotherms
Authors: Rosenfeld Yaakov
Published: February 2003

We propose a framework for calculating equations of state for solids and liquids directly from the experimental zero temperature isotherm. A variational approach with universal reference systems is proposed that incorporates an optimized lattice sum representation for the reference radial distribution function. A tentative lattice sum representation based on the physical picture embodied in the Kerley ad hoc model for fluids is considered for both solids and liquids. By combining models, we show how this approach enables to calculate quantum corrections to the equation of state of the liquid from the Debye temperature of the solid.
Calculation of thermodynamic properties of multicomponent ionic reciprocal systems
Authors: Saboungi Marie-Louise
Published: February 2003

Thermodynamic properties of multicomponent ionic reciprocal systems are derived using the conformal ionic solution theory. The equations obtained are more general than previous equations and depend solely on the properties of the components and on those of the binary subsystems. The behavior of dilute solutions is carefully studied leading to a priori predictions of solubility products in multicomponent systems. The solubility products and the specific bond free energy for making an ion pair, e.g., the pair (A–X) in the binary solvent BY–CY, are shown to depend upon specific ionic interactions in the binary subsystems. The equations presented are compared with equations derived from prior theories.
Spectra and structure of small-ring molecules. XLI. Microwave spectrum of 3-phospholene
Authors: Durig J. R. , Streusand B. J. , Li Y. S. , Richardson L. , Laane J.
Published: February 2003

The microwave spectra of 3-phospholene and 3-phospholene-1-d1 were recorded from 12–40 GHz and 26.5–40 GHz, respectively. Only A-type transitions were observed. The R branch assignments have been made for the ground state of the -d1 molecule, and the ground, first, and second excited states of the ring-puckering mode for the ’’light’’ molecule. It is shown that the skeletal atoms of the five-membered ring are noncoplanar and the ring is puckered by an angle of approximately 18°. Additionally, it is shown that the most stable form of the molecule is the ’’endo’’ form with the P–H bond directed toward the double bond. From relative intensity measurements it is concluded that the first excited state of the ring-puckering mode has a frequency of 160±15 cm−1. From measurements of the Stark effect for the 3-phospholene molecule the dipole moment components were determined to be ‖μa‖=1.10±0.02 D, ‖μb‖=0.0 D (assumed), and ‖μc‖=0.16±0.05 D with the total dipole moment being ‖μt‖=1.11±0.02 D. These results are compared to other similar molecules.
Laser photolysis of UF6: Reactions of the transient UF5 molecules
Authors: Kim K. C. , Reisfeld M. , Seitz D.
Published: February 2003

Laser photolysis of UF6 at 248 nm produces vibrationally and translationally excited UF5 and F. At very low pressures (<0.1 Torr) in a long path-length reaction cell collisional stabilization is inefficient, which tends to increase the lifetime of the transient UF5 molecule. From the kinetic analysis of the UF5 absorption–decay curve and the UF6 depletion measurements the following dimerization and fluorine atom recombination rate constants were determined for 298 K. RRKM calculations were performed for the formed UF6 molecule which indicated the unimolecular decomposition rate constant to be ∼1×106 s−1. The calculated results indicate that in the primary photolysis about 2/5 of the excess energy above the threshold energy was partitioned into the relative translational energy which is in good agreement with the experimental kinetic analysis and also with the available molecular beam data. The translational energy release from the decomposition of the chemically activated UF6 molecule is small and two energetically different UF5 species are suggested.
Collisional studies of the excited state potential energy surfaces of HeH+2: Energy thresholds and cross sections for reactions of helium ions with hydrogen yielding H+, H+2, H+3, HeH+, and H*(n
l)
Authors: Jones E. Grant , Wu Richard L. C. , Hughes B. Mason , Tiernan T. O. , Hopper Darrel G.
Published: February 2003

Beam collision cell apparatuses have been employed to determine the energy dependences of the cross sections for the reactions of He+ with H2 to yield the ionic or luminescent product species H+, H+2, H+3, HeH+, H*(2l), H*(3l), and H*(4l). Distinct thresholds were observed for the formation of H+ at 7.1±0.2 eV, for HeH+ and H*(2l) at 9.0±0.1 eV, for H*(3l) at 12.7±1.0 eV, and for H*(4l) at 14.4±1.5 eV. The analogous reactions of He+ with D2 have also been studied to confirm these results. Secondary thresholds were also detected, and some of the reactions exhibit apparent isotope effects. Polarization is shown not to appreciably affect the cross sections for H* formation. Both H+2 and H+3, but not HeH+ or H*, are observed as products at near thermal collision energies. The experiments which resulted in the detection of the products H2+, H3+, and especially HeH+, as well as the more precise studies of H+ formation, which are reported herein, were suggested by the theoretical analysis. These results demonstrate the enhancement value of an integrated experimental–theoretical approach for the study of state-to-state chemistry.
Infrared intensities and Coriolis interactions in methylene fluoride
Authors: Kondo Shigeo , Nakanaga Taisuke , Saëki Shinnosuke
Published: February 2003

The individual intensities of the Coriolis interacting ν9, ν3, and ν7 bands of CH2F2 molecule were separately obtained through computer simulation technique. A similar analysis was carried out for the ν8 and ν2 diad, and ν9, ν3, and ν7 triad of CD2F2. The intensities of ν1 and ν6 bands of both CH2F2 and CD2F2 molecules were also reexamined. The obtained results were utilized to determine the sign of the dipole moment derivatives with respect to the normal coordinates. An evidence of a failure of the ’’CH stretching criterion’’ was found in the case of the antisymmetric CH stretching vibration of this molecule.
MNDO–MOCIC evaluation of the uracil force field: Application to the interpretation of flavin vibrational spectra
Authors: Bowman W. David , Spiro Thomas G.
Published: February 2003

A normal mode analysis has been carried out on the in-plane vibrations of uracil and three isotopic molecules, N,N-dideutero, C,C-dideutero, and perdeutero uracil, using a molecular orbital calculation (MNDO) to constrain the ratios of off-diagonal to diagonal elements in the compliance matrix (MOCIC). The 81 observed frequencies are calculated with a mean error of 9.7 cm−1. The force constants and normal mode patterns are discussed. The characteristic up-shift of the 1236 cm−1 mode upon N,N deuteration is reproduced by the calculation, and is ascribable to a change in mode composition from predominantly C=O deformation to predominantly C–N stretching, in agreement with the pattern observed for other cyclic imides. The analogous mode in flavin is variable in different flavoproteins and has been suggested to be sensitive to hydrogen bonding at flavin N3. This effect of hydrogen bonding is modeled in the present calculation by increasing the N–H deformation force constant. A similar perturbation of the C=O deformation constants shows that the 1236 cm−1 mode frequency may also be somewhat sensitive to hydrogen bonding at C4=0, but not at C2=0.
Dynamics of gas–surface interactions: Reaction of atomic oxygen with adsorbed carbon on platinum
Authors: Tully John C.
Published: February 2003

Stochastic classical trajectory studies have been carried out of the Rideal-type reaction of gas-phase oxygen atoms with carbon adsorbed on the (111) face of a platinum crystal. Flow of energy between the reaction zone and the crystal has been incorporated in an accurate way. An empirical interaction potential has been employed, based on experimental information about gas-phase CO and about C, O, and CO adsorbed on platinum. Although the interaction potential is uncertain, the major qualitative conclusion of the study—that the product CO molecule escapes quickly from the surface with considerable internal excitation—is unaffected by substantial alterations of the potential. Rotational angular momentum is predicted to be anisotropic, and product angular distributions peaked toward the surface normal. Mechanisms involving excitation of conduction electrons are shown to play a significant but not dominant role in removing energy from the product.
He2(d 3Σu+) decay rate in a high-pressure helium afterglow
Authors: Parker J. W. , Anderson L. W. , Fitzsimmons W. A. , Lin C. C.
Published: February 2003

We report a total collisional quenching rate of (8.2±0.6)×104 Torr−1 sec−1 at 293 °K for He2(d 3Σu) molecules colliding with ground state He atoms. This rate is determined by observing the decay rate of dye-laser induced d 3Σu+→b 3Πg fluorescence over a pressure range of 50 to 700 Torr.
An infrared multiphoton dissociation study of radiative and collisional relaxation of vibrationally excited CF3O− ions
Authors: Jasinski Joseph M. , Brauman John I.
Published: February 2003

Infrared multiphoton dissociation is used in conjunction with pulsed ion cyclotron resonance spectroscopy to measure vibrational relaxation rates for CF3O− ions produced with excess vibrational energy via dissociative electron capture. Upper limits to the rate constants for both radiative and collisional vibrational relaxation are obtained. Collisional relaxation of the ions is found to be rather slow compared to the rates of many ion–molecule reactions.
On the interaction of spherical double layers
Authors: Medina-Noyola Magdaleno , McQuarrie Donald A.
Published: February 2003

The mean spherical approximation of the primitive model of electrolyte solutions is analyzed for the case of two large, charged spherical ions separated by a distance r in a supporting medium of small ions of arbitrary size and concentration. It turns out that the case in which the radii of the small ions is zero (Debye–Hückel approximation) yields a simple analytic solution in agreement with the Verwey–Overbeek asymptotic results for this system. Simple analytic results are employed to illustrate the more general case.
Theory of deviations from the limiting near-dissociation behavior of diatomic molecules
Authors: Le Roy Robert J.
Published: February 2003

The nature of the deviations from the limiting near-dissociation behavior of diatomic molecule properties is investigated. It is shown that for strongly bound species the leading deviations from the limiting behavior associated with the asymptotically dominant Cn/rn potential energy term can be quantitatively attributed to the higher inverse power terms contributing to the long-range potential. The properties of the derived expressions show that experimental vibrational energies should often obey the limiting near-dissociation equation even when the term Cn/rn is responsible for only a fraction of the potential strength at the levels’ outer turning points. In contrast, Bv values (and other properties) are quite sensitive to the presence of additional contributions to the long-range potential, and deviations from their predicted limiting behavior should provide a sensitive new means of determining values of higher-order potential coefficients. The theory is illustrated by and tested against results for B(3Π+0u)-state I2 and for simple model potentials.
Circular intensity differential scattering of light by helical structures. II. Applications
Authors: Bustamante Carlos , Maestre Marcos F. , Tinoco Ignacio
Published: February 2003

Analysis and numerical calculations were made of the total scattering and differential scattering of circularly polarized light by helices as models of chiral structures. The differential scattering patterns are much more sensitive than the total scattering to helical parameters. For large helices the angular dependence of these patterns show lobes which alternate in sign. The number of lobes and the positions of the zeros directly measure the ratios of radius and pitch to wavelength. The signs depend on the sense of the helix. The results are compared with measured circular intensity differential scattering of membranes from the bacterium Spirillum serpens. Good qualitative agreement is obtained.
Angular distribution in the photoelectron spectrum of the ground and first excited vibrational bands of the X 2Σg+ state in N2+ measured as a function of photon energy
Authors: Carlson Thomas A. , Krause Manfred O. , Mehaffy David , Taylor James W. , Grimm Frederick A. , Allen John D.
Published: February 2003

Angle-resolved photoelectron spectra were taken of the first ionization state of N2 as a function of photon energy using a monochromatized beam of polarized photons from the Wisconsin Synchrotron Radiation Center. From these results the angular parameters for the first two vibrational states were determined over a range of photon energies from 17.7 to 31.0 eV. In energy ranges where resonance absorption, accompanied by autoionization, is expected to occur, β for the first excited vibrational level (v1) was frequently characterized by near zero values. In energy regions free of discrete autoionization v1 was found to have a value of β considerably larger (∼0.4 to 0.8 units) than that for the ground vibrational level (v0). This result is shown to be in accordance with recent calculations by Dehmer et al., based on the effect of vibrational motion on β in the vicinity of a shape resonance.
Effects of velocity averaging on the shapes of absorption lines
Authors: Pickett Herbert M.
Published: February 2003

The velocity averaging of collision cross sections produces non-Lorentz line shapes, even at densities where Doppler broadening is not apparent. The magnitude of the effects will be described using a model in which the collision broadening depends on a simple velocity power law. The effect of the modified profile on experimental measures of linewidth, shift and amplitude will be examined and an improved approximate line shape will be derived.
Band shapes in CARS: Background effects and overlapping resonances
Authors: Roland C. M. , Steele W. A.
Published: February 2003

Quantitative intensity measurements are reported for the CARS spectra of the symmetric stretch (ν3) mode in liquid CH3I, the totally symmetric stretch (ν1) in liquid CCl4 and the Q branch for the vibration mode of gaseous N2 at a series of densities. Calculations of the observed band shapes were carried out for both polarized and depolarized bands of CH3I, for the band in CCl4 and for the N2 Q branch at the three lowest densities. Good agreement was obtained after the calculated band shapes were adjusted by varying the values chosen for the nonresonant susceptibility, and for the relaxation times of the vibrational normal coordinates and the reorientation (for the depolarized band). Relaxation times for the liquids and collision broadening factors for the gases are listed; in most cases, the values obtained are more accurate than the corresponding numbers from spontaneous Raman spectra. The problems involved in calculating CARS intensities in the presence of nonresonant susceptibility and overlapping resonances are discussed.
Mechanical characteristics and mechanism of the triboluminescence of fluorescent molecular crystals
Authors: Chandra B. P. , Zink Jeffrey I.
Published: February 2003

The mechanical characteristics of triboluminescence (TL) from coumarin, acenaphthene, resorcinol, phenanthrene, and m-aminophenol crystals are studied. The TL spectra of these crystals resemble their fluorescence spectra. The TL appears concurrently with the sudden force decreases in the fracture regions of the force vs compression curves of the crystals. The decay time of TL from the motion of a single crack is of the order of a microsecond. The dependence of the TL intensity on time, impact velocity, the applied stress, and the crystal dimensions is discussed quantitatively using a phenomenological theory based on the movement and interaction of cracks in the crystals. No systematic correlation of the normalized TL intensity with the photoluminescence efficiency, charge produced during crystal fracture, or the experimental fracture stress is found. No considerable differences are found between the TL intensities of crystals grown in argon and in nitrogen atmospheres when they are crushed inside argon-stripped liquid or in air. Triboluminescence is an intrinsic property of the crystals and is discussed in terms of the piezoelectrification produced during the movement of cracks in the crystals.
On the quantitation of light emission from cytochrome c in the low quantum yield limit
Authors: Champion P. M. , Lange R.
Published: February 2003

A method for the quantitation of light emission is presented which uses the Raman scattering cross section of water as a reference. The method is successfully applied to systems having a known quantum yield, thus providing an independent check of Raman cross-section measurements. A very weak incoherent emission from the ferrocytochrome c system is quantitated (Φ=3.6×10−6) and interpreted using a simple kinetic model which is consistent with the quantum mechanical treatment. The quantum yield measurements imply that the excited state (S1) lifetime of the ferrocytochrome is on the order of 0.2 ps, while the lifetime of the ferricytochrome is deduced to be much shorter. The implications of these measurements concerning the magnitudes of the excited state (S1, S2) damping factors in ferrocytochrome c are also discussed.
The coil–globule transition: Radius of gyration of polystyrene in cyclohexane
Authors: Sun Shao-Tang , Nishio Izumi , Swislow Gerald , Tanaka Toyoichi
Published: February 2003

The temperature dependence of the radius of gyration of polystyrene (MW=2.6×107) in cyclohexane in the good through poor solvent regimes was obtained by analysis of the angular dependence of the autocorrelation function of light scattered from the solution. The observed transition in polymer dimensions through the coil to globule states is in good agreement with the predictions of mean field theory.
Two-photon resonance effect as observed in the CARS and CSRS of anthracene single crystal
Authors: Shimizu M. , Igarashi R. , Adachi Y. , Maeda S.
Published: February 2003

CARS and CSRS spectra of single crystalline anthracene have been investigated in a frequency range of excitation where the effect of TPA resonance is expected. A remarkable resonance effect has been observed in the line shape of Raman signals as well as in the background level height, in the spectra with exclusively b-polarized radiations. The CSRS spectra have been conspicuous by the development of negative Raman peaks, indicating the predominant importance of TPA–Raman interference contribution. By tracing the background level height against Raman peak height, the TPA band profile has been described to have the maximum near 31 400 cm−1 and the bandwidth of about 1000 cm−1.
Fractional ionization and the identification of intercalated species in AsF5–graphite
Authors: Moran M. J. , Fischer J. E. , Salaneck W. R.
Published: February 2003

X-ray photoelectron spectroscopy (XPS), x-ray diffraction, weight uptake, and chemical analyses are correlated with basal conductivity, reflectance spectra, and other electronic properties of C8nAsF5 and its residue compounds. The chemical information shows that no more than 40% of the AsF5 equivalents oxidize the graphite, the rest merely diffusing in as neutral molecules. The XPS results show that less than 30% of the initial intercalated AsF5 is converted to AsF6−, in good accord with determinations of the fractional free carrier generation per molecule. Reactions carried out in the presence of AsF3 show that this species is not an effective reducing agent for the partially oxidized compound C8AsF5. This proves that the AsF5 removed by pumping does not originate in the reverse of the oxidation reaction.
Optical dephasing and vibronic relaxation in molecular mixed crystals: A picosecond photon echo and optical study of pentacene in naphthalene and p-terphenyl
Authors: Hesselink Wim H. , Wiersma Douwe A.
Published: February 2003

Picosecond photon echo and spectroscopic measurements have been used to establish that optical dephasing in the pure electronic and several vibronic transitions of pentacene in naphthalene is induced by pseudolocal phonon scattering in the ground and excited state. The frequency and low-temperature lifetime of this local phonon are 18 cm−1 and 3.5 ps in the groundstate and 13.8 cm−1 and 11 ps in the excited state (vibron independent). The deuterium isotope effect on the local phonon frequency demonstrates its molecular character and suggests its assignment as an in-plane librational mode. For the system pentacene in p-terphenyl photon echo measurements indicate the existence of a librational mode of ?30 cm−1 with a ?1.5 ps lifetime. Line shift measurements on both mixed crystal systems further show that the observed temperature induced shift is due to a difference in quadratic electron–bandphonon coupling of the ground and excited state and crystal anharmonicity (thermal expansion). We further report for a number of vibronic transitions the low-temperature dephasing times. Stimulated picosecond photon echo measurements are used to show that these relaxation times are only determined by population relaxation. No systematic variation is observed between the vibronic relaxation times and excess vibrational energy which indicates that the intramolecular anharmonic coupling determines the initial step in the vibrational energy dissipation process.
Incident ion energy dependence of the secondary photon emission of ion bombarded beryllium
Authors: Wright R. B. , Gruen D. M.
Published: February 2003

Secondary photon emission due to ion bombardment of Be metal foil by 200–3000 eV Kr+, Ar+, Ne+, O+2, and N+2 was studied and the emission yield from four Be (I) and one Be (II) transitions as a function of incident ion energy was interpreted in terms of relevant excitation processes. A model based on a velocity dependent excitation process, the random linear collision cascade theory of sputtering; and making allowance for nonradiative de-excitation of the excited sputtered atoms and/or ions, accounted for the observed energy dependent emission yields. The results of this model indicate that the secondary photon emission yield, Yexi(vm), of a given emission line, i, can be expressed as Yexi (vm) α J(μamp/cm2) S(no./ion) exp[−(A/a)i/vm], where J is the incident ion current density, S the sputtering yield; vm is the velocity corresponding to the maximum transferred energy between the incident ion of energy E1, mass M1, and the target atom of mass M2, i.e., vm=[8M1E1/(M1 +M2)2]1/2; (A/a)i is the effective nonradiative de-excitation parameter for state i. Values for the (A/a)i parameters were found to be 1–3×107 cm/sec for the Be (I) and Be (II) states; a decrease to 5–7×106 cm/sec upon O+2 bombardment was observed for the Be (I) states, while the value for the Be (II) state did not change.
Photoelectron–photoion coincidence study of the bromobenzene ion
Authors: Rosenstock Henry M. , Stockbauer Roger , Parr Albert C.
Published: February 2003

The technique of variable time photoelectron–photoion coincidence mass spectrometry has been applied to the fragmentation of bromobenzene ion producing a phenyl ion. A detailed analysis of the variation of the breakdown curve with parent ion residence time was performed. The results lead to ΔH °f0 (phenyl ion)=270 kcal/mole in close agreement with recalculated results from an earlier study on chlorobenzene. This, combined with other photoionization results leads to ΔH °f0 (phenyl radical)=83±3 kcal/mole, slightly higher than the value 80.9±2 kcal/mole obtained from neutral kinetics. The analysis leads to a rate-energy dependence for the fragmentation process and an equivalent 1000 K Arrhenius pre-exponential factor of ∼9.4×1014 sec−1, which may be compared to the value 2×1015 sec−1 for the analogous neutral process. The possible contribution of spin orbit splitting is discussed.
Interference of electric and magnetic dispersion forces between optically active and inactive molecules
Authors: Chiu Ying-Nan , Kenney Alice V. , Brown Samuel H.
Published: February 2003

Angular momentum and irreducible tensor methods are used to derive the orientation dependence of the interaction energy between two molecules. Attention is given to the second-order energy resulting from the interference of electric and magnetic multipole interactions. Cases covered include (i) molecules with cylindrical interaction symmetry, (ii) one molecule rotating freely and the other fixed in orientation [see Eq.(16)], (iii) both molecules rotating freely [see Sec. IV, Eq. (19)], and (iv) both molecules fixed in orientation [see Eq. (15) and Eq. (22)]. Generalized expressions for the energy are obtained as matrix elements over contractions of irreducible spherical tensors. Explicit expressions, up through electric and magnetic octopole interference, are given. In the lowest order the expression for electric dipole and magnetic dipole interference agrees with the known expression derived by Craig, Power, and Thirunamachandran. New and higher order expressions derived here include interactions between one optically active molecule with another optically inactive molecule, plus interactions between two optically active molecules. Examples of the transformation properties of the multipole operators in the point group symmetry of the molecules are given. These are used to discuss the type of molecules which give rise to specific interactions and the resulting (angular) relationships between the transition multipoles of the two interacting molecules [Eq. (27)].
Sublimation thermodynamics of the URu3 compound
Authors: Edwards J. G. , Starzynski J. S. , Peterson D. E.
Published: February 2003

The sublimation behavior of the URu3 intermetallic compound has been studied with a mass spectrometer–target collection apparatus. The sublimation reaction proceeded by dissociation to the elements up to the solidus temperature of the condensed phase. Vapor pressures of gaseous 233U effusing from the Knudsen cell over the temperature range 1690–2100 K were measured by target collection and radioanalysis of the targets. A second-law treatment of the data yielded ΔH° (1896 K) and ΔS° (1896 K) of sublimation of 563.4±13.4 kJ mole−1 (134.6±3.2 kcal mole−1) and 147.8±7.1 JK−1 mole−1 (35.3±1.7 cal K−1 mole−1), respectively. The corresponding ΔH° (1896 K) and ΔS° (1896 K) of formation were −79.5±20.9 kJ mole−1 (−19.0±5.0 kcal mole−1) and −35.2±10.5 JK−1 mole−1 (−8.4±2.5 cal K−1 mole−1), respectively. Third-law treatment with estimated free energy functions yielded ΔH° (298 K) of sublimation and ΔH° (298 K) of formation of 572.2±8.0 kJ mole−1 (136.8±1.9 kcal mole−1) and −49±22 kJ mole−1 (−12±5 kcal mole−1),respectively.
Studies of H2O on β-AgI surfaces: An effective pair potential model
Authors: Hale Barbara N. , Kiefer Jerry
Published: February 2003

Effective pair potential functions are used to study the adsorption of a water molecule on surfaces of β-AgI. The water molecule is represented by a rigid point charge ST-2 model and the AgI substrate by an array of point atoms with effective charge ±0.6e, Lennard-Jones cores, and ionic polarizabilities. Maximal binding energy surfaces and optimal H2O configurations are generated for the water molecule adsorbed on the rigid and unrelaxed basal and prism AgI faces. Adsorption of the H2O above a two layer ledge, an iodine vacancy, and an H2O trapped in the vacancy are modeled for the iodine basal face and compared with results for the smooth substrates. These studies indicate the H2O adsorption is favored at ’’interstitial’’ sites where no substrate atoms lie directly below either in the first or second layer. The prism face is found to attract the water molecule more strongly and provide larger energy barriers to surface diffusion. The model predicts maximal binding energies of 20 and 16 kcal/mole for the adsorbed H2O on the preferred prism and basal face sites, respectively. The iodine vacancy produces an adsorption site with optimal binding energy 19 kcal/mole and the two layer ledge results in an extended region of strong binding sites of order 20 kcal/mole. The water molecule trapped in the I vacancy creates a surface charge ’’defect’’ around which additional water molecules could cluster with dipole moments in configurations favorable for H2O–H2O bonding.
Density of quantum states of ion–molecule association complex and temperature dependence of radiative association coefficient
Authors: Bates D. R.
Published: February 2003

The density of states of ion-molecule association complexes is derived. The RRKM formulae give the ratio of the total partition function of the association complex to the product of the total partition function of the ion and the molecule. From these, the density of states is deduced. (AIP)
Energy trapping from localized states in mixed organic solids
Authors: Klafter Joseph , Jortner Joshua
Published: February 2003

The possibility of identifying an Anderson transition for electronic energy transfer in the impurity bands of mixed low-temperature, organic solids is discussed. (AIP)
Reply to Comment on ‘‘Experimental test of the Anderson–Mott transition model for excitation transport’’
Authors: Ahlgren D. C. , Kopelman R.
Published: February 2003

It is argued that the critical electronic energy transfer EET concentrations observed in naphthalene2,4 are not accounted for by the Klafler and Fortner1,3,5 models of an Anderson transition. (AIP)
Visual conformational transitions of water soluble polydiacetylenes: Effects of pH and electrolyte on absorption and fluorescence spectra
Authors: Bhattacharjee H. R. , Preziosi A. F. , Patel G. N.
Published: February 2003

Visual conformational transitions (yellow↔red or purple) of some water soluble polydiacetylenes (RC–C≡C–CR)x, where R=–(CH2)3,4OCONHCH2COO−K+ and –(CH2)2,3COO−K+, which is analogous to the helix↔coil conformational transition of polypeptides are reported. The conformational transitions, nonplanar↔planar (or twisted) is introduced by varying the concentration of an electrolyte and the pH, and are characterized by the absorption and emission spectroscopy. The yellow solutions of polydiacetylenes turn red or purple upon increasing the concentration of an electrolyte such as KCl and upon lowering the pH, from-12 to 2. The electrolyte concentration dependent absorption spectra display an isosbestic point at 471 nm. No isosbestic point is observed during pH titration. Explanations are forwarded for this discrepancy. The yellow solutions of all the polymers are found to fluoresce. Depending on the side groups used, the red or purple solutions either fluoresce with a substantial reduction in intensity or do not fluoresce at all. Fluorescence maxima show dependence on λexc when the side group R=Pxn(CH2)2,3COO−K+. Also the maxima of the corrected fluorescence excitation spectra of such polymers are found at different wavelengths than the maxima of the corresponding absorption spectra.(AIP)
An experimental study of two-body time correlations in gaseous xenon
Authors: Groome L. J. , Teitsma A. , Egelstaff P. A. , Mook H. A.
Published: February 2003

The Van Hove scattering function, S(Q,ω), has been measured for xenon gas at five state conditions along the 30 C isotherm using the time-of-flight correlation spectrometer at Oak Ridge National Laboratory (ORNL). The data are normalized by division of S(Q,ω) by the static structure factor so that at each Q value the normalized function has unit area: these curves are bell-shaped and are compared to two kinetic calculations by Dufty and Lindenfeld (unpublished). At the lowest density (0.185×1022 atom/cm3) the experimental data are consistent with the perfect gas and the two models. But at the highest density (0.458×1022 atom/cm3) the data probably differ significantly from these models.
The failure of rigid shell models for rotationally inelastic LiH–He collisions
Authors: Alexander Millard H. , Dagdigian Paul J.
Published: February 2003

A simple rigid-body model for rotationally inelastic LiH–He collisions has been implemented. This treatment assumes impulsive collisions between a point particle and a smooth spherical shell whose center is displaced from the center of mass of the LiH molecule. For a given collision energy the radius and displacement of the shell are adjusted for a best fit to the equipotential contour at this energy on the ab initio surface of D. M. Silver [J. Chem. Phys. 72, 6445(1980)]. Cross sections for transitions from the rotationless j=0 state to all possible final j′ states have been computed in a classical trajectory approach and have been compared to more accurate quantum coupled-states values at Ecol=0.3 eV [E. F. Jendrek and M. H. Alexander, J. Chem. Phys. 72, 6452(1980)]. The results from this simple model differ drastically both in magnitude and their j′ dependence from those obtained in the more sophisticated treatment. While such rigid-body models have been used in the analysis of inelastic scattering experiments, the present study suggests that little physical significance can be attached to the size or shape of the rigid shell contour so obtained.
Atom pair potentials of liquid nitrogen from diffraction data
Authors: Narten A. H. , Johnson E. , Habenschuss A.
Published: February 2003

The structure function of liquid nitrogen at 65 K and a molecular density of ρ=0.01851 Å−3 has been derived from new x-ray diffraction data. The RISM integral equation method was used to obtain a repulsive reference pair potential from this structure function. The results indicate that RISM integral equation method gives reliable repulsive reference potentials.
Infrared chemiluminescence investigation of the reactions of halogen atoms with deuterated ethylene and benzene derivatives
Authors: Moss Mary G. , Ensminger Mark D. , Stewart G. M. , Mordaunt David , McDonald J. D.
Published: February 2003

The technique of arrested relaxation infrared chemiluminescence has been used to investigate the reactions of halogen atoms with various deuterated olefinic and aromatic compounds. From infrared emission spectra of the products, the vibrational energy distributions were measured and then compared to the distributions resulting from statistical partitioning of energy. The reactions studied here are reactions of fluorine atoms with ethylene-d4, vinyl chloride-d3, vinyl bromide-d3, benzene-d6, toulene-d8, chlorobenzene-d5, and bromobenzene-d5 and the reaction of chlorine atoms with vinyl bromide-d3. Nonstatistical product energy distributions were observed for the F+ethylene-d4 and Cl+vinyl bromide-d3 reactions. All other reactions showed a statistical distribution of energy among the modes that were observed. The mechanism of distribution of energy among vibrational modes in intermediate size molecules is discussed in relation to these results.
Relativistic self-consistent-field methods for molecules. I. Dirac–Fock multiconfiguration self-consistent-field theory for molecules and a single-determinant Dirac–Fock self-consistent-field method for closed-shell linear molecules
Authors: Matsuoka O. , Suzuki N. , Aoyama T. , Malli G.
Published: February 2003

A general Dirac–Fock multiconfiguration self-consistent-field (MC SCF) formalism for molecules is presented and the matrix form of the Dirac–Fock MC SCF equations is given for use in the basis set expansion method. As a special case of the general theory, a single-determinant Dirac–Fock SCF theory is derived for closed-shell linear molecules and the expressions are given for the matrix elements, which turn out to be real with a proper choice of phase factor for the basis spinors. The results are presented for H2 and LiH using the Slater-type basis functions and a general discussion of the method and the results is also given.
Diamagnetic shieldings of atoms in molecules and their relation to electronegativity
Authors: Ray Naba K. , Parr Robert G.
Published: February 2003

It is shown that the diamagnetic shielding of an atom in a molecule, the quantity, σMd(α)=(e2/3mc2)〈1/rα〉, is exactly given by the formula where the Rαβe are the equilibrium internuclear distances in the molecule, μ is the negative of the electronegativity of the molecule, and We is the energy of the molecule as a function of the atomic numbers Zα and the net molecular charge Q. Combined with previously given empirical formulas for We (Ref. 1), this formula is shown to provide an easy method to estimate σMd values for atoms in neutral molecules.
Time correlation function theory of the dynamics of helix–coil transitions
Authors: Bose Subir K. , Chernovitz Patricia A. , Emptage Michael R.
Published: February 2003

The relaxation time for the helix–coil transition of polypeptides is calculated by a projection operator technique devised by Mori and Zwanzig. We use a mean field Hamiltonian for the polypeptide, which interacts weakly with a phonon bath. The coupling between the polypeptide and the bath drops out of the lowest order perturbation theory result for the relaxation time. We find a strong dependence of the relaxation time on chain length, and propose that the wide range of experimental relaxation times is due to this dependence and the polydispersity of the polypeptide samples used.
Cluster size distribution for the Ornstein–Zernike correlation
Authors: Huang H. W.
Published: February 2003

In the light scattering of microemulsions and micellar solutions, the Fourier transforms of the density correlation functions of scattering centers often satisfy the Ornstein–Zernike form, const⋅ (k2+ξ−2)−1 to large values of ξ2k2 (sometimes up to ξ2k2?10), where k is the momentum conjugate to the coordinate of the correlation function and ζ the correlation length. In this paper I study the cluster size distributions which give rise to the Ornstein–Zernike type correlations. The clusters are assumed to be rods in one dimension, circular disks in two dimensions and spheres in three dimensions, and their positions are completely random.
Double quantum cross polarization. Heteronuclear excitation and detection of NMR double quantum transitions in solids
Authors: Brunner P. , Reinhold M. , Ernst R. R.
Published: February 2003

The application of Hartmann–Hahn cross polarization for the enhancement and for the detection of NMR double quantum coherence is investigated. The matching conditions and relaxation rates are discussed. It is found, in particular, that the double quantum cross relaxation rate is four times that of single quantum cross polarization. Double quantum cross polarization is utilized for the heteronuclear excitation and detection of nitrogen-14 double quantum transitions in solids.
X-ray photoelectron spectroscopy of polymorphous thallous halides
Authors: Porte L.
Published: February 2003

A comparative x-ray photoelectron spectroscopy study of thallous chloride and thallous bromide in their simple cubic and face centered cubic crystallographic structures is reported. Simple cubic structure is the normal phase and a face centered structure is obtained by epitaxial growth of thin layers on potassium bromide substrate. The x-ray photoelectron spectroscopy appears to be able to distinguish these structural modifications. From one structure to another slight differences are found between the separation of cation and anion core energy levels; the use of an electrostatic point charge model leads us to attribute a more covalent bond in the fcc structures as compared to the sc ones. The evolution of the main structures in the valence band from sc to fcc crystals and from compound to compound are discussed in comparison with available KKR density of states calculations; the general shape of the valence bands as well as the trends in the sequences are fairly well reproduced.