bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton Spin—Lattice Relaxation in Liquid Chloroform
Authors: Dinesh  , Rogers Max T.
Published: February 2004

The proton spin—lattice relaxation time has been measured over the temperature range −54−90°C at 60 MHz in liquid chloroform. At 65°C a minimum relaxation rate is observed and from this the important contributions to the relaxation rate have been estimated at 65°C and a series of lower temperatures. It is shown that the intermolecular dipolar relaxation rate dominates at the lower temperatures but the intramolecular contribution becomes increasingly important with increasing temperature and dominates above about 55°C. The spin—rotational relaxation rate is relatively significant and is larger than the intramolecular dipolar term over the entire temperature range studied. The intermolecular dipolar relaxation rates are in reasonable agreement with values calculated with use of translational correlation times estimated from the self-diffusion coefficients at each temperature. The activation energies for the various relaxation mechanisms are reported.
SCF Calculations of the Electronic States of Magnesium Monoxide
Authors: Schamps J. , Lefebvre-Brion H.
Published: February 2004

Ab initio calculations based on Nesbet's symmetry and equivalence restriction version of the LCAO—MO—SCF method, using an extended double-zeta basis set, have been performed at a number of internuclear separations for six configurations, in order to account for the features of the spectrum of MgO and to ascertain the nature of the ground state. Most arguments coming from both experimental data and theoretical calculations corrected by semiempirical estimates of correlation energy differences between the configurations, are in favor of a closed-shell 1Σ+ ground state, although the lowest Hartree—Fock state is a less correlated 3II open-shell state. Higher-lying observed states (D1Δ and C1Σ−) as well as unobserved ones up to the first ionization limit are accounted for by variational or reliable virtual orbital calculations, and they are presented in an energy-level diagram. In this connection, the properties of the variational 2II and 2Σ+ low-lying levels of MgO+ are discussed. It is then suggested that, in view of this, the unclassified ultraviolet bands should most likely be partly assigned to triplet—triplet transitions involving the very low-lying 3II state. Finally, reasonable predictions about other as yet unobserved band systems are made.
High Order Perturbation Theory for a Generalized Central Field Perturbation of the Three-Dimensional Harmonic Oscillator
Authors: Ehlenberger Alfred G. , Mendelsohn Lawrence B.
Published: February 2004

A method is presented to solve a general even-order perturbation of the three-dimensional harmonic oscillator to any order of perturbation. It is found that using an iterative process it is possible to express the nth order perturbation wavefunction as a sum of 4n terms. These 4n terms depend upon all the lower order perturbation wavefunctions and energy corrections, and may be easily evaluated. It is also shown that accurate results may be achieved for large perturbations if the energy is re-expressed as a Pade approximant. The nine lowest levels of an oscillator perturbed by a quartic term are calculated to tenth order and the results agree qualitatively with the two dimensional mixed harmonic—quartic oscillator results of Bell, Davidson, and Warsop.
Magnetic Circular Dichroism of Impurities in Solids: Allowed Electronic Transitions and the LiF F Center
Authors: Osborne G. A. , Stephens P. J.
Published: February 2004

We discuss the moment analysis of the magnetic circular dichroism (MCD) associated with allowed electronic transitions of impurities in solids. New general expressions are derived for the first four moments of both absorption bands and MCD. Explicit results are calculated for the F-center F band and used to analyze absorption and MCD data obtained for the LiF F center over the range 10–300°K. The F band excited state spin—orbit splitting and orbital g value are found to be 27 cm−1 and 0.59, respectively. Assuming harmonicity and a linear electron—phonon interaction it is also deduced that cubic and noncubic modes contribute comparably to the bandwidth.
Green's Functions in Many-Electron, Second-Order Calculations
Authors: Laurenzi Bernard J.
Published: February 2004

The calculation of second-order physical properties for many-electron systems of interacting particles is presented in terms of two-particle Green's functions and graphs. These Green's functions are known in the atomic case, and therefore practical computations are now possible.
Low-Temperature Heat-Capacity Differences between Glasses and Their Crystals
Authors: Guttman Charles M.
Published: February 2004

It is suggested that the low-temperature heat-capacity difference between glasses and their crystal may be computed by considering the simple process, Cx(Vx) ⇒(a) Cx(Vg) ⇒(b) Cg(Vg), where Cx(Vx) is the constant volume heat capacity of the crystal at its equilibrium volume at normal pressures, Vx, Cx(Vg) is the heat capacity of the substance of identical structure as the crystal but of a volume, Vg, equivalent to that of the glass, and Cg(Vg) is the constant volume heat capacity of the glass. Estimates are made of the change in heat capacity due to step (a) (the change in heat capacity at constant crystal structure due to a volume change) and to step (b) (the change in heat capacity due to disordering at constant volume) for a one-dimensional model of a glass and crystal. These suggest that step (a) contributes more to the heat-capacity difference than does step (b). Contributions to step (a) from a three-dimensional Debye model show reasonable agreement with experiment.
Calculation of Rotational and Vibrational Transitions for the Collision of an Atom with a Rotating Vibrating Diatomic Oscillator
Authors: Eastes Walter , Secrest Don
Published: February 2004

A practical method is presented for computing the T-matrix elements for a rotating, vibrating oscillator. A simple model is used which approximates the features of the He–H2 system. It is found that the rigidrotor approximation is in error even at energies well below the threshold for vibrational excitation. For computation of rotational transitions from the ground to the first accessible excited rotational state, many of the excited rotational transitions may be neglected but some of the excited vibrational transitions must be included. At high energies, it is shown that for any particular transition many of the states not strongly coupled to the states involved in the transition may be neglected. It is found that the computation of T-matrix elements for vibrational transitions in the presence of rotational transitions is not prohibitively time consuming. In computing the total cross section, it is shown that a calculation including only the ground state gives remarkably good results.
Analytic Description of the Condensation Phenomenon Near the Limit of Infinite Dilution Based on the Poisson—Boltzmann Equation
Authors: MacGillivray A. D.
Published: February 2004

Upper bounds of exact solutions of the nonlinear Poisson—Boltzmann equation are used to show rigorously that there is a quasicondensation of counterions about an infinite cylinder carrying a surface charge that |exceeds a certain critical value. These results give some justification for the condensation assumption of Manning in his theory of the behavior of polyelectrolyte solutions near the limit of infinite dilution.
Vibrational Relaxation in Gases—Some Constraints on the Use of Master Equations
Authors: Davis Paul K. , Oppenheim Irwin
Published: February 2004

The master equation for vibrational relaxation of diatomic dilute gases is derived. The derivation begins with the quantum Liouville equation and uses projection operator techniques; it can be extended to dense fluids under certain conditions. A careful discussion of the master equation's range of validity reveals restrictions on the experimental initial conditions and the relevant scattering cross sections.
Magnetic Susceptibility of Tetraamminelithium(Zero) in the Range 1.5–194°K
Authors: Glaunsinger W. S. , Zolotov S. , Sienko M. J.
Published: February 2004

The magnetic susceptibility of the compound tetraamminelithium (zero), Li(NH3)4, has been measured by the Faraday method from 1.5 to 194°K. In the liquid the susceptibility is paramagnetic and shows a small positive temperature coefficient that can be attributed to variation of bandwidth with temperature. At the freezing point, 88.8°K, the susceptibility undergoes a 6% decrease, also attributable to a change in bandwidth. At 82.2°K, where there is a change from cubic to hexagonal structure, the susceptibility shows an abrupt 25% drop and Curie-Weiss behavior down to about 15°K. Below 15°K, the susceptibility flattens out. Two models are presented to account for the observed behavior. In one, Li(NH3)4 is considered to be an antiferromagnetic metal with a Néel temperature of about 10°K; in the other, a nearly degenerate electron gas. Hysteresis at the 88.8°K and 82.2°K phase transitions has also been investigated. Fermi-surface topologies for the cubic and hexagonal phases are discussed on the basis of the magnetic susceptibility measurements and existing x-ray and optical data. The magnetic susceptibilities of pure lithium and pure ammonia have also been measured from 1.5 to 296°K. The lithium susceptibility is small, paramagnetic, and temperature independent both above and below the martensitic transformation. The ammonia susceptibility, which is negative, shows, in absolute value, a small decrease at the freezing point and a temperature-dependent increase below 20°K.
Angular Time-Correlation Functions from Spectra for Some Molecular Liquids
Authors: van Konynenburg P. , Steele William A.
Published: February 2004

Depolarized Rayleigh wing scattering data are reported for liquid chloroform, methyl iodide and methylene chloride. The calculation of orientation correlation functions from these results and from infrared vibration-rotation bands is discussed. Fourier transforms of the infrared bands are corrected for shape changes due to variable refractive index, isotope splitting and hot bands. The resulting correlation functions are primarily a measure of orientational and collision-induced changes in polarizability or dipole moment. It is argued that the collision-induced contributions are important only at short times. The long-time behavior of the correlation functions is then compared with several models for molecular reorientation in liquids, and it is concluded that the motion of these molecules is probably best characterized by models involving random walks in angular momentum space.
Structural Relaxation and Ultrasonic Absorption in Aqueous Solutions of Alkali Halides
Authors: Breitschwerdt K. G. , Kistenmacher H.
Published: February 2004

The ultrasonic absorption in aqueous solutions of a number of alkali halides has been measured in the frequency range 5–100 MHz. Lower as well as higher ultrasonic absorption than in pure water has been found depending on type and concentration of the ions present. A kinetic model of the structural relaxation processes in ionic solutions is presented with which the absolute values of the structural absorption as a function of ion concentration and temperature for different types of ions can be described quantitatively. The analysis of the ultrasonic absorption data of the alkali halide solutions with this model yields information concerning the kinetic properties as well as the number of solvent molecules at different distances from the ions. The relaxational parameters obtained are consistent with other experimental data of water and of the solutions.
Vibrational Relaxation of Laser-Excited CO2-Polyatomic Mixtures
Authors: Stephenson John C. , Wood Robert E. , Moore C. Bradley
Published: February 2004

Laser-excited vibrational fluorescence measurements have given rates for vibrational energy transfer from the asymmetric stretch of CO2 to several polyatomic molecules. Rate constants for energy transfer to the nearly resonant CD stretching vibrations in the deuterated species CD4, CD2H2, CD3Cl, CD3I, C2D2, CD2CH2, and C2D4 are compared to the corresponding normal hydrogen isotopes, and to the alkanes C2H6, C3H8, C5H12, and C6H14. The deuterated molecules are between 2 and 90 times more effective than the hydrogen isotopes at vibrationally deactivating CO2. Cross sections for energy transfer from CO2 to (CN)2, HCN, CH3CN, H2Se, CS2, and OCS are given, and rates for intermolecular and intramolecular energy transfer in several of the collision partners are deduced.
Complete Polarization Study of the Two-Photon Absorption of Liquid 1-Chloronaphthalene
Authors: Monson P. R. , McClain W. M.
Published: February 2004

An apparatus is described which permits the measurement of all three of the parameters governing the polarized two-photon absorption of a fluid. The measurement is performed by using suitable combinations of linear and circular polarized photons. The apparatus permits an experimental check on the basic theory of two-photon absorptions. We find that predictions based on second-order p·A interactions are quantitatively obeyed. Knowledge of all three absorption parameters allows the use of exact symmetry rules to assign the symmetry of the excited state. In 1-chloronaphthalene, we find that the region of greatest absorption (38 000–42 000 cm−1) is governed by a nearly symmetric absorption tensor with nonzero trace, indicating a naphthalenelike Ag−1←1Ag− transition of the molecule. In the weaker region (32 000–36 000 cm−1) the tensor is assymetric with nonzero trace. This means that the weaker band cannot be due to any two-photon allowed naphthalenelike transition. Structure is seen in the spectrum of the parameter (δG− δH)/δF, indicating that it is probably the vibronically induced B2u+1←1Ag−, which is well known, lie close to this energy from one-photon studies. We find that δF and δH are very similar throughout the spectrum, leaving open the possibility that in the theoretical expressions for the two-photon absorption, the sum over states is dominated by a single most important virtual state.
Theory of Reactive Scattering. II. Application of the τ Operator Formalism to a Linear Model for Three Body Rearrangements
Authors: Baer Michael , Kouri Donald J.
Published: February 2004

Coupled operator equations for the rearrangement channel operators ταα and τβα are employed in considering a simple collinear model for three body rearrangement collisions. The model is sufficiently general to permit dissociation of the bound atoms and in a certain limit the model becomes identical with that considered by Hulburt and Hirschfelder. We have been able to obtain analytical solutions for the coupled equations which may be used to calculate reactive and nonreactive scattering probabilities for both, when dissociation can occur and for the model of Hulburt and Hirschfelder. The numerical results for the Hulburt and Hirschfelder nondissociative model agree exactly with the results of Tang, Kleinman, and Karplus, and additional new numerical results are given for the more general model also. The present coupled equations may be generalized to three dimensional reactive collisions in a straightforward fashion.
Absolute Rate Constants for the Reaction of Atomic Oxygen with Ethylene over the Temperature Range 232–500°K
Authors: Davis Douglas D. , Huie Robert E. , Herron John T. , Kurylo Michael J. , Braun Walter
Published: February 2004

Rate constants for the reaction of atomic oxygen with ethylene were measured over a temperature range of 232–500°K using the flash photolysis-resonance fluorescence technique. The rate constant at room temperature was also determined using a flash photolysis-kinetic absorption spectroscopy system and a discharge-flow system coupled to a mass spectrometer. Within the experimental errors of the three techniques, good agreement was found for the rate constant at 298°K. The bimolecular rate constant was also found invariant to changes in both total pressure and reactant concentration. Over the temperature range of the experiments, the rate data could be fitted by a simple Arrhenius expression of the form, k=5.42± 0.30× 10−12 exp[(−1130± 32 cal mole−1)/RT]cm3molecule−1· sec−1.
Upper Limit of Electron Effective Mass in Organic Semiconductors
Authors: Fleming R. J.
Published: February 2004

A model of electrical conductivity in solid-state organic semiconductors developed in an earlier paper (Fleming, 1970) is used to estimate an upper limit of 25 times its rest mass for the effective mass of an electron moving in the paraffinic hydrocarbon octacosane (C28H58) under the influence of an external electric field. This value, based on drift mobility calculations, is one-quarter of that deduced by Kemeny and Rosenberg from their analysis of the pre-exponential factor and compensation rule in certain organic semiconductors. In the present model, impurity electrons are considered to move within one-dimensional wells of width comparable to the length of the paraffin molecule (35.6 Å) and of depth slightly less than its ionization potential (the range 5 eV-8 eV is considered). The electrons tunnel through one-dimensional potential barriers between neighbouring molecules. In agreement with Kemeny and Rosenberg, their effective masses for tunneling and for intramolecular motion are equated. The quoted upper limit of effective mass (25m0) is expected to be valid for most organic semiconductors.
Molecular Orbital Theory of the Hydrogen Bond. II. Dimers Containing H2O2 and H2O
Authors: Del Bene Janet E.
Published: February 2004

Ab initio minimal basis LCAOSCF molecular orbital calculations have been performed on (H2O2)2 and on the mixed H2O–H2O2 dimers. The equilibrium structures and energies of these dimers are presented and analyzed. A cyclic structure is predicted to be most stable for (H2O2)2, while open chain structures are predicted for the mixed dimers. The effect of dimerization on the trans barrier to internal rotation in H2O2 is also discussed.
Pressure Effect on the Coupling Between Rotational and Translational Motions of Monosubstituted Benzenes in the Liquid State
Authors: Assink R. A. , DeZwaan J. , Jonas J.
Published: February 2004

The pressure dependence of the deuteron spin-lattice relaxation times has been measured at 30°C in liquid pyridine-4-d1, fluorobenzene-4-d1, toluene-4-d1, chlorobenzene-4-d1, bromobenzene-4-d1, and benzylcyanide-4-d1. Viscosities at high pressures have also been measured at 30°C. In order to obtain information about the anisotropy of the intermolecular potential energy, the relaxation data were interpreted in terms of the parameter κ introduced originally by Kivelson. There is a correlation between the magnitude of κ and the van der Waals volume of the substituent on the benzene ring. From the results obtained it follows that molecular shape plays a decisive role in determining the degree of coupling between the rotational and translational motions in the molecular liquids investigated. Since the pressure dependence of the deuteron T1 has also been determined for fully deuterated pyridine, fluorobenzene, chlorobenzene, bromobenzene, and nitrobenzene, comparison of these data with those obtained for the monodeuterated compounds allowed us to estimate the anisotropy of the reorientational motions. In agreement with our previous results, we have found that the pressure dependence of the intermolecular proton T1 followed closely the viscosity changes in pyridine and fluorobenzene. Theoretical and experimental activation volumes have been determined both for the rotational and translational motions of the molecules investigated. A comparison of dielectric relaxation data with the NMR data indicates that the molecules reorient by small-step diffusion.
Perturbation Theory for Repulsive Forces in Classical Fluids: Selected Applications
Authors: Sung Stephen , Chandler David
Published: February 2004

The ``blip function'' expansion is a method for describing the equilibrium structure and thermodynamics of repulsive force systems in terms of properties of a hard sphere fluid. In this paper, the expansion is generalized to apply to multicomponent systems in which the intermolecular forces are angular dependent. Several applications are presented which illustrate the usefulness and the limitations of the theory.
Steady State and Transient Phosphorescence Microwave Double Resonance (PMDR) Studies of Aromatic Carbonyl Molecules; Studies of Experimental Conditions and Properties of π-π* Triplet States
Authors: Cheng T. H. , Hirota N.
Published: February 2004

Steady state and transient PMDR studies of several π-π* type aromatic carbonyl molecules were made. The conditions influencing the steady state PMDR signals were investigated and ways of enhancing the steady state signal intensities were discussed using 4-chlorobenzaldehyde (CBA) in 1,4-dibrombenzene host as an example. We studied the effects of microwave sweep width, sweep rates and power levels on the PMDR signals. The experimental conditions to optimize the steady state signals were discussed. The zero field splittings (ZFS) of four π-π* type aromatic carbonyl molecules were determined and compared. It was observed that ZFS are quite different amongst the individual systems. Possible explanations for these large differences are given. The transient PMDR studies were made on CBA in DBB and trimethylbenzaldehyde (TMBA) in durene. The populating and decay rates of CBA in DBB and TMBA in durene were compared. Various cases of nearly complete and partial inversion, partial and near saturation of spin sub-levels were reported. Methods of determining the degree of inversion in different cases were discussed. The roles of local electronic symmetry, triplet state energy transfer and external heavy atom effects in determining these rates are discussed briefly.
Spectral Observations on Molecular XeF6: Raman Scattering and Infrared, Visible and Ultraviolet Absorption in the Vapor and in Matrix Isolation
Authors: Claassen Howard H. , Goodman Gordon L. , Kim Hyunyong
Published: February 2004

Raman spectra and visible and ultraviolet absorption spectra of XeF6 vapor have been studied as functions of temperature. The changes that occur in the observed spectra are interpreted as due to relative population changes of the three electronic isomers postulated in the preceding paper. Evidence is presented that, even at temperatures as high as 100°C, it may take tens of minutes to reach equilibrium among the isomers. Infrared spectra of both XeF6 vapor at 25°C and of XeF6 molecules isolated in a low temperature argon matrix have been studied for a variety of previous thermal treatments of the XeF6 samples. In the spectra of the matrix, large differences in the relative intensities of absorption bands were found, depending on the thermal history of the XeF6 used in the deposition. All the spectra observed are interpreted in terms of the three electronic isomers, and the assignments appear quite plausible.
Distorted Wave Calculation of Vibrational Excitation and Transfer in H2 and D2
Authors: Calvert J. B.
Published: February 2004

A numerical three-dimensional distorted wave calculation has been made for V-T and V-V vibrational excitation cross sections in H2, D2, and their mixtures, for energies within 1.5 eV of threshold. The corresponding relaxation times have been calculated for temperatures between 300 and 1000°K and the results compared with shock-tube and stimulated Raman emission data.
Triplet-State ESR of Cyanine Dyes
Authors: Pierce Richard A. , Berg Robert A.
Published: February 2004

ESR spectra have been obtained for four symmetric cyanine dyes in alcoholic solution at 77°K. Zero-field-splitting parameters show a regular dependence on chain length of the conjugated π-electron system. Molecular-orbital calculations of these parameters show that in some cases, at least, the triplet state is localized in the region of the polyene chains; the experimentally observed splittings and the variations with chain length are reproduced in the calculations. The correlation between properties in the singlet and triplet states is discussed.
Hydrogen Atom Scrambling in Ion-Molecule Reactions of Methane and Ethylene
Authors: Huntress Wesley T.
Published: February 2004

The product distribution for the reactions CH4++CD4, CH3+ + CD4, C2H4++C2D4, and their isotopic complements are determined as a function of reactant ion kinetic energy over the range from thermal energies to 10 eV. The reaction of CH4+ with the parent neutral proceeds both via proton transfer and hydrogen atom abstraction accompanied by approximately 10% hydrogen atom exchange during reaction. The reactions CH3++CD4 and C2H4++C2D4 are shown to proceed with isotopic scrambling of the hydrogen atoms over the entire kinetic energy range from thermal energies to 10 eV. Several endothermic channels are observed at high kinetic energies for the reaction C2H4++C2D4 including the production of C2H2+, C2H3+, C2H5+, and C3H3+ ions.
Resonance Fluorescence of s-Tetrazine and Its Quenching
Authors: Vemulapalli G. Krishna , Cassen T.
Published: February 2004

Fluorescence of s-tetrazine in the collision-free region resulting from excitation into (0′, 0″) and three sequence bands has been investigated. The quantum efficiency of emission from the four corresponding vibronic levels has been determined. A marked variation in the quantum efficiency from level to level and within the envelopes of vibrational bands is found. The quantum yields do not show a systematic decrease or increase with the energy of the vibronic levels. Quenching of the resonance fluorescence by 3-methylpentane and argon has been studied. Bimolecular processes—vibrational deactivation and quenching of total fluorescence—are found to be very inefficient. The number of hard-sphere collisions needed for these processes ranged from 50 to several hundred depending on the vibronic level.
Emission from Dyes in the Vapor Phase and the Possibility of Vapor-Phase Dye Lasers
Authors: Pappalardo R. , Ahmed S.
Published: February 2004

Emission from vapor-phase Rhodamine B and Rubrene has been studied, using for excitation the line emission from argon and krypton ion lasers. Broad emission bands have been found for both vapors. The study suggests that in the temperature range 300–400°C rapid relaxation processes occur within the excited electronic level of Rubrene vapor, while these processes are slower for Rhodamine B. The emissivity per unit length of Rhodamine B and Rubrene were found to be approximately five times smaller than the corresponding emissivity of Rhodamine B solution, in the concentration range known to lase even under flashlamp excitation. From the study it is inferred that laser action should occur in these vapors.
Measurement and Analysis of the ν3 Band of Methane
Authors: Barnes W. L. , Susskind J. , Hunt R. H. , Plyler E. K.
Published: February 2004

The ν3 band of CH4 has been recorded with a spectral resolution of 0.016–0.019 cm−1 in the region from 2884 to 3139 cm−1. The manifolds containing the allowed lines were subsequently deconvoluted and 198 allowed and 86 forbidden lines were measured and tabulated. Line frequencies and intensities were calculated using the Hamiltonian as extended by Susskind and are listed for the 284 experimental lines which have been assigned. The rms difference in the measured and calculated frequencies for the 211 allowed transitions with upper state J ≤ 12 is 0.0078 cm−1. The 18 molecular constants used to culate the rotation-vibration fine structure frequencies are compared with previous values and found to have uncertainties which are generally at least an order of magnitude smaller than those given previously.
Site Assignment of Fe3+ in Low Symmetry Crystals. Application to NaAlSi3O8
Authors: Michoulier J. , Gaite J. M.
Published: February 2004

A new method of site assignment of Fe3+ in low symmetry crystals is presented. This method is based on the fact that the fourth order spin-Hamiltonian constants of Fe3+ are sensitive mainly to the immediate surroundings of the Fe3+. It is shown how it is possible to find the pseudosymmetry of the fourth order term of the spin Hamiltonian, while from the pseudosymmetry it is possible to define the orientation of the Fe–On complex in the structure and to localize Fe3+ in the crystal. To use this method the spin-Hamiltionian constants must be well known. The determination of the 20 constants of a general spin Hamiltonian is described. To apply our method in a low symmetry case, we studied Fe3+ in NaAlSi3O8, which has a triclinic lattice. Experiments were done on a single crystal at Q band frequency. The spin-Hamiltonian constants are given. It is shown that Fe3+ is in a T1(0) site and substitutes for Al3+.
Vibration
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Vibration
Energy Transfer in CO2-Hydrogen Halide Mixtures
Authors: Stephenson John C. , Finzi Jack , Moore C. Bradley
Published: February 2004

The relaxation of the asymmetric stretching vibration of CO2 was observed in mixtures with HCl, DCl, HBr, DBr, HI, and DI. The observed cross sections were relatively large for vibration-vibration exchange between CO2(0001) and HX (v=1). For HCl and DCl the cross sections were about 0.5 Å2 and decreased slightly with increasing temperature in the range 298–510°K. The cross sections decrease more rapidly with increasing energy difference between the vibrations for the deuterium halides than for the hydrogen halides. Energy transfer to the HX or DX rotational degree of freedom may be responsible for this difference. Existing approximate theories of vibrational energy transfer due to long range multipolar forces do not quantitatively explain the data. However, for CO2–HBr, CO2–DCl, and CO2–HI, calculations show that it is possible that multipolar interactions could make significant contributions. The rate at which vibrational energy is removed from the CO2(0001) and HX (v=1) levels is usually much slower than the exchange between them. The deactivation rates due to CO2-hydrogen halide collisions could usually only be determined as a weighted sum of the deactivation of CO2(0001) by HX and HX (v=1) by CO2. Rates for deactivation of CO2(0001) by HCl and of DBr (v=1) by CO2 were established at room temperature within 25% ranges. The deactivation rates are much faster than for CO2(0001) with rare gases and molecules such as N2. The data suggest the hypothesis that energy transfer among the vibrations of CO2 is aided by attractive forces and transfer to rotation in CO2(0001)-hydrogen halide collisions.
Hydrogen Bonding in Acetic Acid/Acetone Mixtures
Authors: Rassing Jo/rgen
Published: February 2004

It is shown that the ultrasonic relaxation caused by hydrogen bond formation in acetic acid/acetone mixtures cannot be explained in terms of a self-association of acetic acid. The interaction of acetone, which is a strong hydrogen bond acceptor, must be introduced. The simplest way of introducing the solvent interaction is to assume that the hydrogen bonds present are established between acetic acid and acetone molecules only. However, this consideration leads to disagreement with the experimental data. It is demonstrated that a two state model which describes the kinetics of the system in terms of a transition between two states of different energy, a hydrogen bonded state, and a non-hydrogen-bonded state leads to a complete agreement with all the experimental data. Closed dimers of acetic acid, open dimers of acetic acid linked to acetone by a hydrogen bond, and monomers of acetic acid linked to acetone by a hydrogen bond contribute to the bonded state, while monomers of acetic acid and acetone contribute to the nonbonded state. The equilibrium constant and the rate constants for the transition between the two states are calculated.
Zero-Phonon Transition and Fine Structure in the Phosphorescence of Fe3+ Ions in Ordered and Disordered LiAl5O8
Authors: Pott G. T. , McNicol B. D.
Published: February 2004

Phosphorescence and excitation spectra have been measured in Fe3+-doped ordered and disordered LiAl5O8. A good fit with the Tanabe-Sugano diagram for a high spin d5 configuration with B=644 cm−1 and C=2960 cm−1 has been obtained. From the calculated 10 Dq value of 8000 cm−1 and a comparison with the excitation spectra of Fe3+ in β-NaAlO2 it has been shown that the spectra are due to Fe3+ ions in tetrahedral interstices. A sharp zero-phonon transition has been observed in the low-temperature phosphorescence and excitation spectra of the ordered phase of LiAl5O8 and its occurrence was found to be correlated with an anomalously small Stokes shift of 500 cm−1. X-ray powder diffraction, phosphorescence, and ESR spectra show that there exist only two phases of LiAl5O8, an ordered and a disordered phase. Evidence is given that the previously postulated metastable phase is a phase with incomplete ordering.
Self-Consistent Molecular Orbital Methods. XIV. An Extended Gaussian-Type Basis for Molecular Orbital Studies of Organic Molecules. Inclusion of Second Row Elements
Authors: Hehre Warren J. , Lathan William A.
Published: February 2004

We have recently proposed an extended basis of atomic functions expressed as fixed linear combinations of Gaussian functions for hydrogen and the first row atoms [Ditchfield, Hehre, and Pople, J. Chem. Phys. 54, 724 (1971); Hehre and Pople, J. Chem. Phys., 56, 4233 (1972)]. We now extend our treatment to consider atoms of the second row. This basis set is close to minimal in that each inner shell atomic orbital is represented by a single function and only valence shell orbitals (3s, 3p) are extended, these being split into inner and outer parts. No functions of higher quantum number than are necessary in the ground state atom are included. We have considered the effect of molecular environment on the size of the valence shell orbitals and have proposed a ``standard set'' of scaling factors.
Intravalence and Extravalence Excitations of the Ethylene Molecule in Liquid and Solid Rare Gas Matrices
Authors: Miron Eli , Raz Baruch , Jortner Joshua
Published: February 2004

In this paper we present the results of a spectroscopic study of the absorption spectra of ethylene and ethylene-d4 in liquid argon, liquid krypton, and solid krypton in the spectral region 2000–1400 Å. The samples involved 1 cm thick doped liquids and 1 cm thick doped krypton crystal (doping level 1–10 ppm). The intravalence nature of the N→V transition was confirmed. On the basis of some general criteria based on vibrational structure, vibrational isotope effects, matrix shifts, and line broadening we were able to provide a definite identification of the lowest Rydberg state of ethylene and of ethylene-d4 in solid krypton. The effect of the liquid-solid phase transition on the line broadening in the lowest Rydberg state was elucidated. We were also able to provide the first experimental observation of the n=2 impurity Wannier state originating from the molecular positive ion in liquid argon.
ESR Studies of Some Manganese(III) Dithiocarbamates Diluted in Cobalt Analogs
Authors: Golding R. M. , Sinn E. , Tennant W. C.
Published: February 2004

Electron spin resonance results at 77°K are presented for a series of manganese(III) dithiocarbamates diluted in the cobalt(III) analogs using both single crystal and powder techniques. The observed spectra are shown to arise only from the addition of manganic dithiocarbamates to the cobalt salt. No fine or hyperfine structure was observed and the paramagnetic species seems unlikely to be due simply to a d4 Mn3+ ion.
Negative Ion Formation and Negative Ion-Molecule Reactions in Cyclopentadiene
Authors: di Domenico A. , Harland P. W. , Franklin J. L.
Published: February 2004

The low pressure source of a Bendix time-of-flight mass spectrometer has been employed for a study of positive and negative ion formation in cyclopentadiene (C5H6). Six negative ions in the mass spectrum of C5H6 have been investigated and particular attention has been paid to the cyclopentadienyl negative ion (C5H5-). The appearance potential data for C5H5+ and C5H5- ion formation were used to estimate the following previously unknown thermochemical parameters: Δ Hf(C5H5-) = 19 ± 2 kcal mole-1, Δ Hf(C5H5) ≤ 70 ± 5 kcal mole-1, Δ Hf (C5H5+) ≤ 273 ± 4 kcal mole-1, E.A.(C5H5) ≤ 2.2 ± 0.3 eV, and D(C5H5–H) ≤ 3.9 ± 0.2 eV. A high pressure source was employed to carry out negative ion-molecule proton transfer and proton plus hydrogen transfer reactions between C5H5 and a variety of reactant ions. An evaluation of the energetics for these processes provided a second approach for the estimation of a value for Δ Hf(C5H5-) and also gave an upper limit of 58 kcal mole-1 for Δ Hf(C5H4-).
Variational Approach to the Prediction of Excess Thermodynamic Properties of Binary Liquid Mixtures. IV
Authors: Mansoori G. Ali
Published: February 2004

The variational technique which is proposed earlier [J. Chem. Phys. 53, 1931 (1970)] is applied for the prediction of the excess thermodynamic properties of binary liquid mixtures. The results are compared with the experimental and machine-calculated, Monte Carlo, data. Also comparisons are made with the results of the other theories of mixtures. It is shown that the variational technique is a stronger tool for quantitative predictions of the excess thermodynamic properties of liquid mixtures than the other existing theories of mixtures.
Detection of Argon Cluster Fragmentation in a Time-of-Flight Mass Spectrometer
Authors: Milne Thomas A. , Greene Frank T. , Beachey Jacob E.
Published: February 2004

The method developed by Franklin et al. to deduce information about the kinetic energy of fragment ions from the ion peak shape in the Bendix time-of-flight mass spectrometer has been applied to molecular beams of argon clusters. The particular simplicity of analysis with molecular beam species is shown. Results of peak shape studies on free jets of argon indicate substantial contributions to Ar2+ from higher clusters at 50 eV when extensive nucleation has occurred.
Dipole Moment of ICI
Authors: Herbst Eric , Steinmetz Wayne
Published: February 2004

The J = 2 ← 1 microwave spectra of I35Cl and I37Cl are measured for the v=0 and v=1 vibrational levels. The dipole moment μ (v = 0) = 1.24 ± 0.02 D is determined by Stark effect measurements. Improved values of the rotational and quadrupole coupling constants are obtained and the iodine nuclear spin—rotation constant is determined.
Density Gradient Measurements of HCl Dissociation in Shock Waves
Authors: Breshears W. D. , Bird P. F.
Published: February 2004

The dissociation of HCl in mixtures of 5%, 10%, and 20% HCl in Ar in the temperature range 3500–7000°K and in pure HCl in the range 3000–4000°K has been studied behind incident shock waves. Dissociation rates were determined by measurement of postshock density gradients using a laser-beam deflection technique. The postshock density gradient profiles exhibit the same highly characteristic ``dip'' observed previously with O2-rare gas mixtures [J. Chem. Phys. 55, 4017 (1971)], and the magnitude of the gradient at this point is again interpreted as a measure of the initial dissociation rate. The rate coefficients thus obtained for the mixtures of 5%, 10%, and 20% HCl exhibit a high degree of precision and yield the result kHCl–Ar = 4.78 × 1013 exp(-82 700 / RT) cc/mole· sec, with R in calories/mole·degree, for the rate coefficient due to HCl–Ar collisions, in good agreement with other reported values. These same data yield an apparent rate coefficient due to HCl–HCl collisions, kHCl–HCl, which satisfactorily describes the data obtained for pure HCl, with kHCl–HCl ≅ 10 kHCl–Ar. The temperature dependence of kHCl–HCl departs from Arrhenius form, with the apparent activation energy increasing at lower temperatures.
Boltzmann's Equation for a Generalization of Rigid Ovaloid Molecules
Authors: Hoffman D. K.
Published: February 2004

A form for the collision integrals of the linearized Boltzmann collision operator for a gas of rigid ovaloid molecules which also interact through a soft potential is derived which explicitly separates the effects of core collisions from those of the soft interactions. The computation of these integrals using methods previously developed for rigid ovaloid molecules is discussed for the case where the soft potential is spherically symmetric or is very weak.
Lattice Dynamics of Rhombohedral Sodium Azide
Authors: Rafizadeh Hamid A. , Yip Sidney , Prask Henry
Published: February 2004

The external vibrational modes of rhombohedral NaN3 have been studied by means of normal mode calculations and inelastic neutron scattering measurements on powder samples. Phonon dispersion curves and displacement weighted frequency distributions have been computed using force-constant models in which the coupling parameters are determined by fitting the long-wavelength optical frequencies and through the use of interatomic pair potentials. The azide ion is treated in two ways, with and without internal distortions. In both cases short-range interactions involving nearest and next-nearest neighbors are considered in carrying out the lattice calculations. Electrostatic interactions are treated using the standard method of Kellermann and the effective ionic charge is taken to be a parameter. The present method of specifying the model force field enables us to undertake a parameter-free comparison between the calculated and observed spectra of neutrons inelastically scattered from polycrystalline samples of NaN3. Theoretical cross sections have been obtained in the incoherent approximation, but the good agreement between calculations and measurements over an appreciable range of momentum transfers suggests that specifically coherent effects are probably small in the present experiment. Since the neutron data provide a reasonably detailed and quite independent test of the lattice dynamical models, we conclude that the present descriptions of vibrational properties of NaN3 should be adequate for most applications.
Electric Deflection of Molecular Beams of the Lanthanide Di- and Trifluorides, ScF3 and YF3
Authors: Kaiser E. W. , Falconer W. E. , Klemperer W.
Published: February 2004

Electric-deflection studies on molecular beams of the lanthanide trifluorides have been carried out in the temperature range 1000–1200°C. Substantial refocussing, indicative of polar distortions, has been observed for LaF3, GdF3, and LuF3. Weaker refocussing was present in TmF3. CeF3 and ErF3 showed refocussing barely above the noise level. Defocussing was observed in PrF3, NdF3, TbF3, DyF3, and HoF3. Observations on SmF3, EuF3, and YbF3 were inconclusive due to sample reduction in the oven but showed no refocussing attributable to the respective trifluorides. ScF3 and YF3 showed refocussing of a magnitude similar to the trifluorides of La, Gd, and Lu. Deflection studies on the three known lanthanide difluorides revealed that SmF2, EuF2, and YbF2 are strongly polar molecules in the vapor phase and must, therefore, have highly bent structures.
Theory of NMR Line Shape of Alternate Linear Chains of Inequivalent Nuclei Coupled by Indirect Exchange Interaction
Authors: Ayant Y. , Belorizky E. , Gagnaire D. , Taieb M.
Published: February 2004

The NMR spectrum of a linear chain containing two types of spin 12 nuclei, with slightly different chemical shifts, and coupled by a scalar exchange interaction between nearest neighbors, is examined theoretically. Analytical expressions for the first even moments of the spectrum are given and the dependence of the moments on the number of spins in the chain is analyzed. After a brief review of the Liouville representation, a Green's function theory in this representation is developed allowing the study of the line shape. It is shown that in the central region of the spectrum, one obtains an approximately Lorentzian shape whose width is calculated for a weak field experiment. The theory also provides an approximate value for the line intensity at the center of the spectrum for an arbitrary resonance frequency.
Adsorption of Rare Gas Atoms on Xenon
Authors: Hagen Donald E.
Published: February 2004

The problem of adsorption of rare gas atoms on solids is treated for the case of submonolayer films. An energy spectrum calculation method which is suitable for band structure or heat capacity calculations is discussed. It is particularly useful for adsorbate-substrate systems in the region intermediate between ``tight binding'' and ``plane wave'' behavior. The method employs a technique introduced by Kohn and Luttinger of using the eigenfunctions corresponding to a particular point in the Brillouin zone as a basis set. The cases of He and Ne adsorbed on Xe are discussed.
Laplace Transform Method in the Theory of Ion Neutralization. Application to Scavenging Probability in the γ Radiolysis of Dielectric Liquids
Authors: Abell G. C. , Mozumder A. , Magee J. L.
Published: February 2004

A numerical method is presented for the solution of the Smoluchowski equation describing the diffusion and reaction of an isolated ion pair in a dielectric medium in the presence of a scavenger. The method provides upper and lower bounds to the exact solution and a practical means for improving these bounds. A quantitative understanding of the neutralization and scavenging processes associated with isolated charge pairs is now demonstrated to be possible. This holds for all times and for all scavenger concentrations. Calculations are performed for various initial separations of the ion pair, and the results are compared with the scavenging experiments of Schuler et al. A comparison is also made with the results obtained by the method of ``prescribed diffusion.''
Statistical Mechanics of the Parallel Hard Squares in Canonical Ensemble
Authors: Ree Francis H. , Ree Taikyue
Published: February 2004

The Monte Carlo method was used to generate canonical-ensemble isotherms for N=25, 64, 100, and 400 parallel hard squares in a two-dimensional periodic box. The Monte Carlo realizations with their chain lengths ranging up to ∼ 8× 105 trials per particle were employed to ascertain statistical accuracy of the calculated pressures. The resulting isotherms are monotone increasing functions of the density with a possibility of a higher-order transition but without showing any sign of a first-order phase transition, with a density increment greater than 0.005ρ0 (ρ0 is the close-packed density). This departs remarkably from the behavior of the hard-disk isotherm, which displayed a van der Waals-like loop for N ≳ 72. Instead, it resembles isotherms of the lattice-gas systems (e.g., a square-lattice system with the first and second nearest-neighbor exclusion, or a system of dimers) which, like the present case, contain a residual degree of freedom at close packing. By numerically integrating the Monte Carlo isotherms, the constant which corrects the entropy expression of the self-consistent free-volume theory at close packing was evaluated. The resulting value (2 ln2+0.268± 0.004) for the N=400 case agrees satisfactorily with the corresponding value (2 ln2+0.26042) predicted from the cell-cluster theory for the checkerboard structure. The N dependence of the Monte Carlo isotherms was examined in both the low- and the high-density regions. In the low-density region, the Monte Carlo data are in satisfactory agreement with theoretically predicted values, whereas, in the high-density region, the MC data revealed existence of the N -dependent contribution to the pressure attributable to the correlated slidings of rows or columns of particles. This can occur even at 95% of the close-packed density for N≤ 100.