bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Structure of HoAu2
Authors: Atoji Masao
Published: February 2004

Neutron-powder diffraction measurements reveal that HoAu2 (the tetragonal body-centered CaC2-type structure) becomes an antiferromagnet below TN(α) = 9.2°K with the onset of an incommensurate moment alignment (α) having a transverse wave modulation. The α magnetization wave with the wavelength, 6.373 Å = 1.229 a, propagates along the a axis and is polarized approximately in the direction of the b axis, all in the face-centered lattice description. At TN(β) = 7.8°K, a commensurate transverse magnetization wave (β) starts to grow. The β wave with the wavelength equal to the a spacing propagates along the a or b axis and is polarized in the direction of the c axis. The composite configuration of the α and β transverse waves may be described as an antiferromagnetic triangular-fan structure. In cooling, the α wave amplitude reaches rapidly to a maximum value of 6.7 μB at 6.3°K, then decreases monotonically, and diminishes near 0°K. The β wave moment follows the Brillouin curve and approaches 6.4 μB at 0°K. The composite ordered moment rises to a maximum value of 7.8 μB at around 5.5°K and declines toward 6.4 μB at 0°K. These moment values which are considerably smaller than 10 μB of the free Ho3+ ion indicate a strong crystal field effect. The phenomenum that the maximum composite moment occurs near the midpoint of the ordered phase is due likely to a strongly anisotropic, competing interaction between the RKKY exchange coupling and the crystal field effect.
Time-of-Flight Analysis of Neutral Products from Inelastic Ion-Molecule Collisions
Authors: Conrads R. J. , Pomerance W. , Moran T. F.
Published: February 2004

Cross sections for inelastic charge transfer reactions producing neutral excited atoms have been measured for the interactions of 500 to 1500 eV He+ ions with He. Time-of-flight methods coupled with post acceleration techniques have been used to separate the neutral from charged products of ion-molecule reaction. The position of inelastic peaks appearing in the neutral product energy loss spectra are consistent with the excitation of colliding particles to known spectroscopic excitation potentials with the relative importance of inelastic scattering decreasing as the reactant ion kinetic energy is lowered.
Raman Band Contours. Some Prolate Symmetric Top Molecules
Authors: Masri F. N.
Published: February 2004

New values of Coriolis ζ constants for some prolate symmetric top molecules are determined from observed gas-phase Raman band contours using a generalized Raman-infrared computer program. Using arguments based on the forms of the normal coordinates, it is shown that these values are supported by known ζ values for a number of related molecules. These values also give good agreement between predicted and observed gas-phase infrared band contours. The relative merits of Raman and infrared band contour calculations for these molecules are discussed.
Quantum Lattice Dynamics of Molecular Solids. I. General Theory
Authors: Jacobi Nathan
Published: February 2004

A quantum lattice dynamics formulation is presented for molecular solids, including translational and librational modes. The variational principle is used to construct ground and excited state wavefunctions obeying the translational symmetry of the crystal. For translational modes the formalism reduces to a form similar to previous quantum lattice dynamics treatments. The results for librational modes are new. General properties of the librational wavefunctions and matrix elements are derived for linear molecules interacting through arbitrary anisotropic pair potentials.
Quantum Lattice Dynamics of Molecular Solids. II. Application to the Librations of Solid CO2, α-N2, and o-H2
Authors: Jacobi Nathan , Schnepp O.
Published: February 2004

The quantum mechanical lattice dynamics formalism developed in the preceding paper for molecular solids is applied to the librational modes at k=0 in solid α-N2, CO2, and o-H2, interacting through a quadrupole-quadrupole potential. Librational wavefunctions are constructed for α-N2 and CO2, and free rotor wavefunctions were used for librons in solid o-H2. It is found that the quantum-mechanical lattice frequencies provide nonnegligible, though not dramatic, corrections to the frequencies calculated in the classical harmonic approximation. For α-N2 the quadrupole potential provides a satisfactory description of the anisotropic potential, with the quantum-mechanical frequencies significantly closer to experiment than the classical ones. For CO2 the quadrupole potential provides only part of the anisotropic potential.
Probabilistic Interpretation of Cluster Function Series Development of Many-Electron Wavefunctions
Authors: Hertia D. I. , Ivanov Al.
Published: February 2004

A probabilistic treatment of the polyfermionic systems is made. The idea of the particles localizability on bounded sets in the X-configuration space of the system is used. The decomposition of this space into a union of bounded sets permits a natural decomposition of the wavefunction into a cluster function series. Our purposes are (a) a physical interpretation of this type of expansion and (b) the establishment of a definition for the correlation phenomenon independently of a Hartree-Fock or other particular model.
Theoretical Studies of Collision-Induced Transitions between Molecular Rotational Energy States
Authors: Prakash Vinod , Boggs James E.
Published: February 2004

A method is presented to calculate the rates of collision-induced transitions on the basis of collision-broadening theory. The rates are calculated for important collisional transitions responsible for the change in intensity ΔI/I of the signal transition observed in double resonance experiments involving H2CO, HDCO, H2CCO, HCN, and DCN. The values of ΔI/I derived from the calculated transition rates agree satisfactorily with the measured ΔI/I.
Infrared Spectrum of Matrix-Isolated Nitrous Oxide
Authors: Hisatsune I. C.
Published: February 2004

Nitrous oxide, generated by the in situ thermal decomposition of hydroxylamine hydrochloride or ammonium nitrate, was isolated in some pressed alkali halide matrices. Its three infrared active fundamentals appeared at room temperature as single peaks and without the gas phase rotational structures. Cooling of the host matrix caused these bands to sharpen and to shift to higher frequencies. At any given temperature, however, the peak frequencies were essentially independent of the host matrix. The temperature dependence of the most intense ν3 fundamental was examined in detail, and the results indicated that there were two dominant trapping sites for N2O in pressed KCl, KBr, and KI matrices. Furthermore, the relative concentrations of N2O occupying these sites changed reversibly as the temperature was varied from about 90°K, our lower limit, to over 200°K. From these concentration changes, it was deduced that the transfer of a N2O molecule from the low temperature trapping site to the high temperature site was an endothermic process by 1.2 ± 0.2 kcal/mole and was accompanied by a large increase in entropy of 9.0 ± 1.0 eu in all three potassium halide matrices.
Correlation Effects and Molecular Tumbling in NMR Studies of Solid β-(CH3)4Si
Authors: Albert Shmuel , Ripmeester John A.
Published: February 2004

The β phase of high purity samples (99.9% min) of tetramethylsilane (TMS), (CH3)4Si, was investigated between 77°K and its melting point (174°K) employing static and rotating frame proton spin-lattice relaxation (T1 and T1p, respectively) measurements. Minima in the T1 curve near 90°K and in T1p at 171°K correspond to methyl group reorientation and over-all molecular tumbling, respectively. Activation energies and inverse frequency factors for both motions are derived and discussed. Deviations from exponential behavior in the longitudinal relaxation were noted below 140°K and are inferred to be due to a correlation in the relative motion of the protons within each methyl group. The exponentiality of the spin-lattice relaxation above ∼140°K is associated with the onset of over-all molecular tumbling motions. It is suggested that the presence of exponential proton magnetization decays in solids containing methyl groups may sometimes serve as an indication of the presence of reorientations of the molecular frame to which the methyl groups are attached. The possibility that the existence of exponential and nonexponential decays may be used by itself to gain information on interactions and motions in solids, has to be further investigated.
Quantum and Anharmonic Effects on the Temperature and Mass Dependence of Rate Processes in Solids
Authors: Franklin Wilbur M.
Published: February 2004

The contributions to the temperature and mass dependence by quantum statistical effects in the harmonic approximation are shown to give rise to terms proportional to T−2n and m−n, respectively, where n=1,2,· · ·. It is shown, explicitly, that anharmonic terms make no contribution to the mass dependence in the classical case, except in second order. An analysis of the temperature dependence of the pre-exponential part of the diffusivity, for one atomic mechanism, including anharmonic effects, reveals, for Cu, that deviations from a constant value occur only at high temperatures in the classical case. On the other hand, quantum effects cause a positive curvature at low temperatures. The very small variation of D0 with temperature provides a proof that Arrhenius-type behavior is nearly correct in the classical case despite anharmonic contributions to D0.
Electron Paramagnetic Resonance of Gd3+ in Single Crystals of Various Rare-Earth Ethyl Sulfates at Room Temperature and at 77°K
Authors: Gerkin Roger E. , Thorsell David L.
Published: February 2004

Electron paramagnetic resonance studies of Gd3+ in single crystals of Ln(C2H5SO4)3· 9 H2O (where Ln3+ denotes La3+, Pr3+, Nd3+, Sm3+, Tb3+, Dy3+, Ho3+, Er3+, Yb3+, and Lu3+) have been carried out at X band at room temperature and at 77°K. The spin Hamiltonian parameters b20, b40, and b60 and g‖ have been evaluated at both temperatures for each host except terbium ethyl sulfate at 77°K. The absorption linewidths for each transition have been measured at both temperatures. The present results are compared with previous results. A principal conclusion is that the magnitude of b20 for Gd3+ in the various rare-earth ethyl sulfates is more nearly a linear function of the ionic radius of the trivalent host ion than of its atomic number.
Existence of the Dielectric Constant in Rigid-Dipole Fluids: The Direct Correlation Function
Authors: Ramshaw John D.
Published: February 2004

The question of whether the dielectric constant ε exists (is well defined) for a finite fluid system of rigid dipolar molecules is reconsidered and reformulated. It is found that this question can most simply be expressed in terms of the behavior of the position- and orientation-dependent direct correlation function c(r1, ω1; r2, ω2). It is shown that ε exists if c satisfies the following two conditions: (a) c∼−φ/ kT for |r1−r2| > σ, where φ is the dipole-dipole potential and σ is a length which is large microscopically but small macroscopically. (b) c(r1, ω1; r2, ω2) is of the form c8(|r1− r2|)+ F(r1−r2):e(ω1) e(ω2) for |r1−r2| < σ, where e(ω) is the unit vector with orientation ω. An explicit (and new) expression for ε in terms of c is automatically obtained; its applicability is ensured if the above conditions are satisfied. These results lend new intuition and insight into the question of the existence of ε, and suggest a promising approach for future investigations of this question.
Hindered Rotor States for the Planar H + H2 Reaction
Authors: Walker Robert B. , Wyatt Robert E.
Published: February 2004

A numerical procedure for solving the rotational differential equation for the planar H + H2 reaction in natural difurcation coordinates is described. The procedure has the advantage that it may be applied uniformly over the entire range of the reaction coordinate. The symmetry of the differential equation is utilized to simplify the form of the wavefunctions, and their asymptotic behavior provides a state labeling criterion. The conditions under which any pair of energy levels may become either identically or nearly degenerate is investigated. It is shown that as the reactants approach the transition state (s=O), the rotational wavefunctions smoothly pass through forms characteristic of free rotation, hindered rotation, and finally of a bending vibration. At s=O, equal probability density is shown to be highly localized at the entrance of each rearrangement channel.
Many-Electron Wavefunctions Expanded in Spin-Adapted Antisymmetrized Products, and Their Expectation Values
Authors: Salmon William I. , Ruedenberg Klaus
Published: February 2004

Unrestricted configuration-interaction wavefunctions are constructed according to certain conventions which simplify the calculation of expectation values when S is a good quantum number. General wavefunctions are expressed in terms of antisymmetric space-spin functions that are eigenstates of S2 and Sz and form a complete orthonormal set. The building blocks, called ``spin-adapted antisymmetrized products'' or SAAP's, are designed to take advantage of double occupancy. It is shown that SAAP's, when constructed from orthonormal space orbitals, can be handled in multiconfigurational calculations more easily than Slater determinants. Simple formulas are derived for matrix elements of observable operators expressible in terms of one- and two-electron integrals.
Implementing the SAAP Formalism. I. Serber-Type Spin Eigenfunctions by Direct Diagonalization
Authors: Salmon W. I. , Ruedenberg K. , Cheung L. M.
Published: February 2004

A method is given for generating Serber-type spin eigenfunctions for use in expansions of general electronic wavefunctions in terms of spin-adapted antisymmetrized products (SAAP's). The procedure is efficient and avoids the large storage requirements of spin-coupling schemes using Wigner coefficients. Running times of computer programs are given.
Effect of Vibrational Anharmonicity on Hydrogen-Deuterium Exchange Equilibria Involving Ammonia Molecules
Authors: Bron J. , Wolfsberg Max
Published: February 2004

The anharmonicity correction to the zero-point energy of isotopic ammonias is theoretically evaluated. The G0 term, which is usually ignored, is found to make a significant contribution to this correction. The comparison of the corrections leads to the conclusion that the anharmonicity corrections to the isotopic self-exchange equilibria among the ammonias are negligible. Other correction factors to the self-exchange equilibrium constants calculated in the usual harmonic approximation are also considered and found to be quite negligible. The calculated self-exchange equilibrium constants are compared with experiment and good agreement is found. Agreement is also found between theory and experiment for the isotopic exchange equilibrium constant between ammonia and hydrogen.
Translational Absorption of HeH
Authors: Ulrich Bruce T. , Ford Lewis , Browne J. C.
Published: February 2004

There is reported here the calculation of the translational absorption spectrum of a system of a helium atom and a ground state hydrogen atom. We report also values of calculated potential curves for the ground state of the molecular system HeH and the dipole moment of the ground molecular state of HeH as a function of internuclear separation. The behavior of the dipole moment is of particular interest as it passes through zero at about R=7a0. This change of sign follows from and correlates with the known long range behavior of the dipole moment of this system.
Effusion. VIII. Orifice Transmission Probabilities as a Function of Pressure for a Near-Ideal and for Right-Circular Cylindrical Orifices
Authors: Wey Song Jey , Wahlbeck P. G.
Published: February 2004

Orifice transmission probabilities (defined as the ratio of the number of molecules leaving an orifice into vacuum to the number of molecules entering the orifice from a gas container according to the kinetic theory of gases) have been determined for 15 orifices with length to diameter ratios from 0.02 to 9.53, with a pressure of CsCl vapor from 3.7 × 10−3 to 1.826 torr corresponding to values of the Knudsen number (ratio of mean free path to orifice diameter) from 17.6 to 0.051. Total effusion measurements have been made using both a multiple cell effusion method and a vacuum balance apparatus. The data agree well with previous experimentally determined values, with Clausing orifice transmission probabilities for large K calculated by DeMarcus, and with values calculated from equations derived by Wahlbeck. It is now possible to calculate vapor pressures from transition region data provided the molecular diameter is known.
Effusion IX. Application of the Failure-of-Isotropy Theory for the Effusion of Gaseous Mixtures
Authors: Wey Song Jey , Wahlbeck P. G.
Published: February 2004

The kinetic theory of gases provides predictions of mean free paths for a gaseous species in a gaseous mixture. The failure-of-isotropy theory of Wahlbeck may be applied to each individual species for the calculation of angular number distributions and orifice transmission probabilities. Results from calculations for the ideal orifice are presented. Calculated angular distributions are compared with experimental angular number distribution data for a thin-edged orifice measured by Grimley and LaRue.
Quantum Mechanical Studies of the Vibrational Excitation of H2 by Li+
Authors: White R. Allen , Hayes Edward F.
Published: February 2004

The quantum mechanical equations of motion for the vibrational excitation of an harmonic are solved via the set of coupled Volterra equations describing that motion. The numerical techniques which allow accurate inclusion of closed channels are developed. The equations are solved for an ab initio interaction potential and for a model potential. The ab initio interaction potential gives results in poor agreement with experiments. A comparison with the results of a two-parameter model potential, which can give results close to the experimental results, provides some insight into features of the surface which are important for vibration excitation.
Complex and Unrestricted Hartree-Fock Wavefunctions
Authors: Ostlund Neil S.
Published: February 2004

The general conditions under which real, restricted Hartree-Fock wavefunctions become unstable with respect to variation of the orbitals are derived. It is shown that complex solutions to the Hartree-Fock equations are associated with a singlet instability in the usual real, restricted solution. A comment is made concerning the complex wavefunctions found by Harris and Pohl for hydrogen halides at short internuclear distances.
g=4.3 Isotropic EPR Line in Tourmaline
Authors: Ja Y. H.
Published: February 2004

An isotropic EPR line with g=4.302±0.006 was found in a natural single crystal of tourmaline. This line can be ascribed to the impurity Fe3+, occupying a host site with the axial field parameter D=0 and the rhombic field parameter E ≫ hν. After an inspection of the environments of different hostcation sites, it is believed that Fe3+ ion replacement of the B3+ host site is most likely responsible for this isotropic line.
Unified Treatment of Two-Center, Two-Electron Integrals. I. Electron-Repulsion, Spin-Spin, and Spin-Orbit Integrals Over Slater Functions
Authors: Milleur Mac B. , Matcha Robert L.
Published: February 2004

Utilizing the Neumann expansions of the electron-repulsion operator, all two-electron two-center spin-spin, spin-orbit, and electron-repulsion, hybrid, Coulomb, and exchange integrals arising in computations of expectation values of the respective operators over wavefunctions written as linear combinations of Slater functions are expressed in terms of a simple formula requiring, effectively, a one-dimensional numerical integration. A general formula for one-center integrals is also derived by utilizing the Laplace expansion of the electron-repulsion operator.
Coupling of Optical Phonons to the T1 ← S Transition in p-Dibromobenzene Crystals
Authors: Colson Steven D. , Gash Bruce W.
Published: February 2004

High resolution spectra of the T1 ← S0 transition in p-dibromobenzene crystals have revealed that the coupling of optical phonons to the transition is much weaker than believed previously. By accounting for phonon coupling, an upper limit of about 15 cm−1 has been established for the total electronic band width of the T1 state. The zero phonon lines are very sharp and are more intense than the phonon addition bands. In fact, the zero phonon line of the (0, 0) transition is so sharp (<1 cm−1 fw at hh) and intense that it can be observed in a crystal ∼ 0.1 mm thick. The major difference between this work and previous work is the spectroscopic resolution. At lower resolution where the spectral linewidth is narrower than the slit width, crystals of several millimeters thickness are required to observe the transition, and the spectrum is distorted in that the broad phonon lines are relatively enhanced. Also, the previously reported temperature dependence of the zero phonon lines can be ascribed to line broadening and not to intensity enhancement with increasing temperature. The order of magnitude increase in sensitivity obtained by going to high resolution may be a quite general phenomenon for triplet states of aromatic molecules making them much more accessible to spectroscopic study than believed previously.
Analysis of the Internal Rotation of the · CF2CONH2 Radical as Observed by ESR in Irradiated Trifluoroacetamide Single Crystals
Authors: Bogan C. M. , Kispert L. D.
Published: February 2004

The temperature-dependent ESR spectrum of the · CF2CONH2radical (found in x-irradiated single crystals of trifluoroacetamide) has been measured at both 9 and 35 GHz over the temperature range from 77 to 290°K. A model is proposed which explains the observed temperature dependence in terms of a torsional oscillatory motion about the C–C bond with a barrier height, V0=3100 cal. Nonadiabatic spin exchange is used to account for the doublet splitting of the central line at 77°K changing to a single sharp line at all angles at 290°K. The exchange rate is described by the empirical equation r−1=3.6 × 108 exp(−410 cal/RT).
Photoionization of N2, O2, NO, CO, and CO2 by Soft X Rays
Authors: Van Brunt R. J. , Powell F. W. , Hirsch R. G. , Whitehead W. D.
Published: February 2004

The total and relative abundances of thermal energy ions produced by absorption of 0.28, 1.25, and 1.5 keV x rays in N2, O2, NO, CO, and CO2 and the dissociative ionization cross sections at these energies were measured using a mass-spectrometric technique. The results demonstrate that there is a significant change in the character of the ionization at the K-absorption edges of the atomic constituents. At these energies dissociative ionization predominates for all the molecules accounting for over 95% of the ions formed at energies above the K edge. Quasistable doubly charged molecular ions make a significant contribution to the thermal energy ions at energies above the K edge. Our results for the total abundances of thermal singly and doubly charged molecular ions are compared with recent measurements by Carlson and Krause.
Photochemistry of Dimethyl Ether at 1470 Å
Authors: Meagher James F. , Timmons Richard B.
Published: February 2004

The room temperature vacuum uv photolysis of dimethyl ether at 1470 Å has been investigated. The main products were found to be H2, H2CO, C2H6, and CH4. In addition, some CH3OCH2CH2OCH3 and CH3CH2OCH3 were identified. The effects of free radical scavengers (C2D4 and H2S) and added inert gas (C2F6) were studied. Molecular elimination processes were found to account for a relatively small fraction of the total product yield. A mechanism has been proposed to account for the major experimental observations.
Photoelectron Spectroscopy of High-Temperature Vapors. II. Chemical Bonding in the Group III Monohalides
Authors: Berkowitz J. , Dehmer J. L.
Published: February 2004

The He(I) photoelectron spectra of InCl, InBr, and InI are presented. A general description of bonding in all Group III monohalides is given on the basis of these new data, earlier data on thallium monohalides, ab initio calculations on BF, AlCl, and GaCl, and semiempirical calculations on all of the Group III monohalides. It is found that a molecular orbital localized on the electronegative atom in an ionic diatomic molecule is appropriately classified as ``bonding''; whereas a molecular orbital localized on the positive ion has an ``antibonding'' character. This classification is qualitatively different from that used to discuss covalently bound molecules.
Carbon-13 Impurity Effect on the a2u Infrared Exciton Spectrum of the Benzene Crystal
Authors: Laufer J. C. , Kopelman R.
Published: February 2004

The C-13 shift for the a2u molecular benzene mode has been calculated to be −0.33 ± 0.04 cm−1. This confirms our previous assignment of the major pairwise molecular excitation exchange interactions for the a2u vibrational exciton and enables us to pick an exciton density-of-states for the pure crystal. We also calculate the natural-abundance isotopically mixed benzene crystal density-of-states and its spectrum. Predicted in-band spectral resonances are consistent with published experimental data and facilitate their interpretation in terms of Davydov components, density-of-states peaks, band center, site shift, and exciton interactions. The implications and applications of the C-13 presence in ``pure crystal'' spectra are discussed.
Kinetic Energy Release in the Dissociation of Some Simple Molecular Ions. Water and Hydrogen Sulfide
Authors: Jones E. G. , Beynon J. H. , Cooks R. G.
Published: February 2004

The technique of ion kinetic energy spectroscopy has been applied to a study of S+. formation from H2S+. and O+. formation from H2O+.. Unimolecular formation of S+. occurs by predissociation of the first excited state via the repulsive 4A2 state of H2S+.. Above the classical crossover region this reaction proceeds rapidly on the mass spectrometer time scale but tunneling through the barrier occurs slowly and gives rise to metastable ions which fragment with conversion of all the available potential energy to kinetic energy. Collisional excitation of ground state H2S+. yields excited ions which rapidly dissociate via the 4A2 repulsive surface to give substantially excited (v=2) H2. This reaction occurs with the partitioning of some 30% of the available energy into translational energy of the products. The heat of formation of S+., determined from the appearance potential, requires only slight correction for the excess energy term arising from the potential energy difference between the crossover region and the ground state of the products because the repulsive surface is unusually flat. Ground state H2O+. ions undergo collision-induced excitation with loss of 22± 4 eV of kinetic energy to give a high energy excited state which fragments directly to give O+. (2D or 2P) and vibrationally excited H2. Appearance potential measurements do not provide a reliable assignment of the products because of the excess energy terms. These results are in contrast to earlier conclusions that fragmentation upon electron impact yields two hydrogen atoms.
ESR Studies on Radical Conversions in Irradiated Single Crystals of Succinic Acid
Authors: Muto Hachizo , Inoue Tetsushi , Iwasaki Machio
Published: February 2004

The ESR studies on the radical conversions from primary to room temperature stable radicals in irradiated single crystals of succinic acid have been carried out with aid of fumaric acid-doped crystals. Since in the doped crystals the spectrum of succinic acid anion was replaced by that of furmaric acid anion, it was possible to identify the spectrum arising from ĊH2CH2COOH, which has been postulated for a long time as a precursor of the room temperature stable radical CH3ĊHCOOH. It has been further found that a part of ĊH2CH2COOH converts into HOOCĊHCH2COOH at − 100°C and then the radical isomerization from ĊH2CH2COOH to CH3CHCOOH takes place at − 100 − ∼ − 75° C following the conformational change which is favorable to the intramolecular hydrogen transfer. The freshly formed CH3CHCOOH radical has a different conformation from that of the room temperature stable species. The stable conformation is achieved by the 180° rotation around the C–C bond between the CH and carboxyl carbon atoms in the unstable species. Besides these, the conversion process from the succinic acid anion to HOOCĊHCH2COOH and HOOCCH2CH2C=O has been also studied. These results are based on the hyperfine and g tensors determined in the present work for CH2CH2COOH and unstable and stable CH3ĊHCOOH as well as the stable anion.
Crystal Field Energy Levels and Zeeman Spectra of Dy3+ Lanthanum Ethyl Sulfate, in the Near Infrared
Authors: Gourley J. T.
Published: February 2004

The theoretical energy level scheme and g∥ values for the 6H11/2 level of Dy3+ in La ethyl sulfate have been determined using both L–S and intermediate coupling. The corresponding experimental values have been found using fields up to 50 kG. These compare favorably with the theoretical predictions. Crystal field splittings and g∥ values have also been obtained for the ground state 6H15/2 and these also agree with previous results and calculations.
Magnetic Properties of Fe3+ Ion in Frozen Ferric Perchlorate Solutions
Authors: Ohya Toshie , Ôno Kazuo
Published: February 2004

Mössbauer effect of 57Fe has been used to study the magnetic properties of Fe3+ ions in frozen ferric perchlorate aqueous solutions. The Mössbauer data for solutions with pH higher than about 2.5 can be understood by a model in which Fe3+ ions form antiferromagnetic fine particles that show superparamagnetism above the blocking temperature. In applied magnetic fields, unambiguous ``anisotropic spin relaxation'' spectra in the superparamagnetic state are observed. The decrease in susceptibility at room temperature may be also explained by this model. The solutions with low pH show paramagnetic spectra even at low temperatures.
Solutions of the Nernst-Planck Equations for Ionic Diffusion for Conditions near Equilibrium
Authors: Malvadkar S. B. , Kostin M. D.
Published: February 2004

The time-dependent Nernst-Planck equations are used to derive analytical expressions for the ionic concentrations and electric potential as a function of position and time as equilibrium is approached. For sufficiently large values of time it is shown that the concentrations of cations and anions approach equilibrium with the same exponential decay constant, for which an explicit formula is derived. It is also shown that even for large times deviations from electroneutrality occur. A comparison of the analytical solutions is made with the numerical solutions, which are calculated by solving the time-dependent Nernst-Planck equations on a digital computer. Excellent agreement is obtained.
Core Polarization of NH4Br:Cu2+
Authors: Narayana P. A. , Sastry K. V. L. N.
Published: February 2004

Analysis of the EPR spectrum of NH4Br:Cu2+ single crystals has indicated that the unpaired electron is in d3z2−r2 orbital. Both isotropic and anisotropic parts of the hyperfine interaction with the ligand nucleus have been obtained by simulating the EPR spectrum. It is observed that covalency has a very significant effect on the core polarization. The calculations have indicated that 3% of 4s character is necessary to obtain a good value for the contact term.
Electron Paramagnetic Resonance of Cupric Ion Pairs in Zn1−x Cux 2,6-Pyridinedicarboxylate
Authors: McMillan J. A. , Cravens D. J.
Published: February 2004

Copper-doped zinc 2,6-pyridinedicarboxylate (dipicolinate) exhibits electron paramagnetic resonance absorption characteristic of a coupled pair of cupric ions in low symmetry, as attested by observed transitions at half-field. Intensity measurements performed at different temperatures indicate that the triplet state lies lower, and have permitted the determination of the coupling parameter J. A study of the main spectrum in polycrystalline samples has led to approximate values of the magnetic parameters characterizing Zeeman, hyperfine, and zero-field terms. From the Zeeman and hyperfine parameters, and a study of the optical absorption, electron wavefunctions in each ion have been derived. Approximate values for the electron localization in excited states are also proposed. Values for the distance between ions have been calculated after an analysis of the zero-field splitting parameter.
Catalytic Efficiencies of H2O, D2O, NO, and HCl in the Vibrational Relaxation of HF and DF
Authors: Blauer J. A. , Solomon W. C. , Sentman L. H. , Owens T. W.
Published: February 2004

The catalytic efficiencies of H2O, D2O, NO, and HCl in the vibrational relaxation of HF and of NO in the vibrational relaxation of DF were investigated over the temperature and total pressure ranges of 1000 to 4100°K and 0.1 to 0.3 atm, respectively. Measurements were made in an Ar diluent behind incident shock waves. The extent of vibrational excitation in HF was determined as a function of time by continuously monitoring the infrared emission intensity at 4150 ± 200 cm−1. Water appears to relax HF principally by means of a direct transfer of vibrational energy (V–V) between the collision partners. Furthermore, its collisional efficiency was found to be in fair agreement with the results reported by others for the analogous process of HCl relaxation by H2O. Nitric oxide was found to be at least an order-of-magnitude more efficient as a collision partner in the vibrational relaxation of HF than is known for either of the molecules N2 or O2. A small amount of data regarding the effect of HCl upon the vibrational relaxation of HF was collected. Within the temperature range considered, its catalytic efficiency was found to be comparable to that of HF itself.
Transport Properties of a Gas of Diatomic Molecules. V. GPS Calculation of the Rotational Relaxation Time of the Ar–N2 System
Authors: Olmsted Richard D. , Curtiss C. F.
Published: February 2004

The moments of the probability density function for rotationally inelastic scattering of the Ar–N2 system were computed, in Paper XVI of a series on molecular collisions, by both generalized phase shift (GPS) and classical trajectory (CT) methods. In the present paper, it is shown that inclusion of the term of zero order in h/ in a semiclassical expansion of the generalized phase shift modifies the classical limit expressions for the moments. The Ar–N2 system is reconsidered and the first and second moments calculated to the lowest nonzero order in the anisotropy of the interaction potential. The results of this calculation indicate a marked improvement of the first moment over the previous GPS results as compared with the CT results. The development is extended by integrating the moments over the impact parameter and the translational and rotational energies to obtain rotational collision numbers for the Ar–N2 system. These collision numbers are compared with those obtained by classical trajectory methods.
ESR of the BS Molecule in Inert Matrices at 4°K
Authors: Brom J. M. , Weltner W.
Published: February 2004

ESR spectra of 11BS and 10BS molecules in their ground 2Σ+ states were measured while isolated in solid neon and argon matrices at 4°K. g tensors and hyperfine structure constants for interaction with 11B and 10B were determined. In neon the magnetic parameters for BS are  g∥11=2.0016(1), g⊥=1.9942(1), A∥(11B)= 853.3(3) MHz, and A⊥ (11B)=766.7(3) MHz. Observation of weak ESR signals attributed to 33S hfs yields | A⊥ (33S)|=16 (2) MHz. The observed Δ g⊥ is in excellent accord with the magnitude and sign of the spin-doubling constant, γo, as derived from published gas phase optical data. A CNDO calculation of the ground state wavefunction for BS was made and used to compare calculated spin densities and g values with experimental values. A comparison of the chemical bonding in BS and BO is given.
Raman Spectra of Gases. III. 2,5-Dihydropyrrole, Trimethyleneimine, and 1-d-Trimethyleneimine
Authors: Carreira L. A. , Carter R. O. , Durig J. R.
Published: February 2004

The Raman spectra of 2,5-dihydropyrrole, trimethyleneimine, and 1-d-trimethyleneimine in the gas phase have been recorded. Both Δv=1 and Δv=2 transitions have been observed for the ring-puckering mode. The Δv=1 transitions were quite weak for trimethyleneimine which seems to be consistent with the asymmetry of the ring-puckering wavefunctions.
Rotational Relaxation in Dilute Gas Mixtures
Authors: Gelb Alan , Wilson C. Woodrow , Kapral Raymond , Burns George
Published: February 2004

The relaxation of rigid rotator molecules dilutely dispersed in a bath of inert gas molecules is investigated. The systems studied correspond to hydrogen and hydrogen deuteride molecules in an excess of helium and neon, and hydrogen fluoride in an excess of helium. Fairly accurate quantum mechanical estimates of the potential energy governing the translation to internal energy transfer process have been used in this investigation. In those cases where the interaction energy was not available from previous work (H2–Ne and HF–He systems) the appropriate calculations were carried out to determine this quantity. Approximate solutions to the Boltzmann equation which describes the relaxation process were obtained by expanding the distribution function in orthogonal polynomials and evaluating the necessary integrals by a Monte Carlo method. The properties of the rotational energy autocorrelation function and relaxation time are examined.
De-excitation of CO2(00°1) by Hydrogen Fluorides
Authors: Shin Hyung Kyu
Published: February 2004

Vibrational de-excitation of CO2(00°1) by HF and DF molecules is investigated on the basis of vibration-to-rotation energy transfer in the temperature range 300°–2000°K. The calculation shows that the vibrational relaxation is very fast in both CO2 (00°1) -HF and CO2(00°1)-DF collisions, and the results are in reasonable agreement with laser-excited fluorescence measurements around 350°K. For CO2 (0001) -HF, an inverse temperature dependence of the relaxation time is found between 300° and 400°K; the relaxation time at 360°K is about 30% longer than that at 300°K. For this system the relaxation times change from 0.023 μ sec·atm at 300°K to 0.0035 μsec· atm at 2000°K. No inverse temperature dependence is found for CO2 (0001) -DF. From a comparison with experimental data it is predicted that the deexcited-states of CO2 are (00°0) and (0110), respectively, for the CO2 (0001) -HF and CO2 (0001) -DF relaxation processes. The difference in the final states is explained in terms of the relative efficiency of HF and DF in de-exciting CO2(00°1). Throughout the calculation, the effects of translational motion and molecular attraction on relaxation processes are considered.
Kinetics and Mechanism of the Formation of Water Cluster Ions from O2+ and H2O
Authors: Howard Carleton J. , Bierbaum Veronica M. , Rundle Howard W. , Kaufman Frederick
Published: February 2004

The reaction sequence leading from O2+ to H3O+· H2O was examined in He, Ar, N2, and O2 carrier gases in a flowing afterglow system. The rate constants for the reactions were measured and the kinetic analysis for their determination is presented. For M=N2, two new steps involving the formation and reaction of O2+· N2 were proposed and examined. The rate constants are discussed and compared with other experimental values.
Instability of the Uniform Antiferromagnetic Chain. I. XY Model in the Adiabatic Approximation
Authors: Beni G. , Pincus P.
Published: February 2004

We investigate the thermodynamic properties of a linear chain of elastically coupled spins with an antiferromagnetic interaction between them in the XY model and the adiabatic approximation. This system exhibits a second order phase transition and a magnetic susceptibility which vanishes at absolute zero. The effects of magnetostriction are considered and shown to affect neither the order of the transition nor the qualitative behavior of the magnetic susceptibility.
Wavelength Effects in Fluorescence Quenching. Aromatic Hydrocarbons Quenched by Carbon Tetrachloride
Authors: Ware William R. , Lewis Colin
Published: February 2004

The origin of wavelength effects in the fluorescence quenching of aromatic hydrocarbons by chlorinated alkanes has been investigated using fluorescence lifetime and fluorescence steady-state techniques and absorption spectroscopy. Evidence was obtained for the presence of ground-state complexes between the aromatic hydrocarbon and the chlorinated alkane in both polar and nonpolar solvents. The kinetics of the fluorescence quenching are consistent with the hypothesis that these ground-state complexes are responsible for the variations of the quenching efficiency with wavelength.
Shock Tube Calorimeter for the Dissociation Energy of Fluorine
Authors: Blauer Jay , Solomon Wayne
Published: February 2004

The shock tube was used as a calorimeter to determine the dissociation energy of molecular fluorine. Mixtures of F2, HF, and Ar were shock heated to temperatures between 1400 and 3200°K and allowed to approach dissociative equilibrium. The equilibrium temperature was determined by monitoring the HF equilibrium radiant intensity at 2.5 μ. The resultant value of D0oKo of 37.1± 1.2 kcal/mole was compared with the recent results of other authors.
Cascade Deactivation and Pressure Dependent Nonequilibrium Kinetic Isotope Effects for Chemically Activated Dichloroethane-d and -d4 Molecules
Authors: Setser D. W. , Siefert E. E.
Published: February 2004

The competition between unimolecular dehydrohalogenation and collisional deactivation of chemically activated 1,2-C2H4Cl2, =88.3 kcal mol−1, and 1,2-C2D4Cl2, =89.3 kcal mol−1, formed by combination of CH2Cl and CD2Cl radicals at 300°K has been investigated in CH3Cl(CD3Cl), CO, Ne, and He bath gases. For each gas, the kinetic isotope effect, ka (H) /ka (D), was measured over a wide pressure range. Within experimental error, all gases gave the same isotope effect at high pressure; ka∞(H)/ka∞(D=3.2± 0.2. At lower pressures the isotope effect markedly increased and for the lowest pressures the rate constant ratio was ∼8. Cascade vibration deactivation is shown to be the source of the pressure dependence of the kinetic isotope effect. The cascade deactivation of C2H4Cl2 and C2D4Cl2 by CH3Cl(CD3Cl) and CO was adequately described by a stepladder model with average energy losses per collision of 6 and 4 kcal mol−1. For Ne and He bath gases, an exponential model with average energy losses of 2.9 and 1.4 kcal mol−1 was satisfactory. There was no specific isotope effect on the collisional transition probabilities for C2H4Cl2 and C2D4Cl2.
Vibrational Energy Transfer Probabilities of Highly Vibrationally Excited Dichloroethane with Argon, Krypton, Xenon, and Sulfur Hexafluoride
Authors: Setser D. W. , Siefert E. E.
Published: February 2004

The competition between unimolecular reaction and collisional deactivation of chemically activated 1,2-C2H4Cl2, 〈 E〉 = 88 kcal mol−1, was studied using Ar, Kr, Xe, and SF6 as bath gases. Sufficient data were collected to establish the high pressure rate constant and the increase in the rate constant with declining pressure for each gas. The results were fitted to a cascade deactivation scheme using gas kinetic collision diameters to define the collision frequency. Exponential transition probability models were assigned to argon and krypton with average down transition probabilities per collision of 3.5–4.5 kcal mol−1, which is substantially larger than the average energy removed by He and Ne. Xenon could be fitted by this model, or by a stepladder model with 〈Δ E〉 = 5 kcal mol−1. A stepladder model with an average down transition probability of 7 kcal mol−1 was assigned to SF6. The experimental results that have been accumulated (12 gases) for collisional deactivation of 1,2-C2H4Cl2 are summarized.
Determination of the Heats of Atomization of the Molecules RhC2, RhC, and TiC2 by High Temperature Mass Spectrometry
Authors: Cocke D. L. , Gingerich K. A.
Published: February 2004

The mass spectrometric Knudsen effusion technique has been used in the determination of the thermodynamic properties of the gaseous molecules RhC, TiC2, and RhC2 over a TiP–Rh–C system. The third law enthalpies, ΔH0o, in kcal of the reactions (1) Rh(g)+C(graph)=RhC(g), (2) Ti(g)+2C(graph)=TiC2(g), (3) Rh(g)+2C(graph)=RhC2(g), (4) RhC2(g)+Rh(g)=2RhC(g), (5) TiC2(g)+Rh(g)=RhC2(g)+Ti(g), and (6) RhC(g)=Rh(g)+C(g) have been determined as 33.1± 0.5, 62.0± 0.8, 93.6± 1.1, −26.0± 0.7, 32.2± 1.3, and 137.4± 0.9, respectively. The second law value of ΔH0o corresponding to Reaction (1) is 29.7±0.6 kcal. These reaction enthalpies have been combined with appropriated literature data to yield the dissociation energy D0o(RhC)=138.0± 2.0 kcal mole−1 and the heats of atomization, Δ Hatm,0o[RhC2(g)]=247± 5.0 kcal mole−1 and Δ Hatm,0o[TiC2(g)]=277± 2.0 kcal mole−1. The bond dissociation energies, D0o, for Rh–C2 and Ti–C2, have been determined as 105± 5 and 135± 4 kcal mole−1, respectively. The standard heats of formation, Hf,298o, of gaseous RhC, TiC2, and RhC2 have been derived as 164.1± 2.3, 174.4± 2.1, and 225± 5 kcal mole−1, respectively.
Sequence Dependence of DNA Hypochromism
Authors: Pysh E. S. , Richards John L.
Published: February 2004

We report time dependent Hartree calculations of the hypochromism of mixed sequence DNA segments. Self-consistent field nucleotide wavefunctions are accurate enough to show some of the observed sequence dependence of DNA hypochromism. The results of time dependent Hartree theory are shown to be consistent with empirical sequence analyses that have been reported. On the basis of this consistency we can say that conclusions based on the empirical analyses are also well founded in theory. Specifically, (a) DNA hypochromism is not expected to have a simple linear dependence on AT content; (b) DNA's that have a random nearest neighbor frequency distribution will show a quadratic dependence of hypochromism on AT content which is approximately linear over any fairly large range of AT content; (c) past observations of near linearity for some DNA's were a direct consequence of those DNA's having a nearly random nearest neighbor frequency distribution; and (d) DNA's which deviate from the expected dependency have nonrandom nearest neighbor frequency distributions.
Paramagnetic Hyperfine Interactions in a t2g4 Configuration of 57Fe
Authors: Paez E. A. , Weaver D. L. , Oosterhuis W. T.
Published: February 2004

Mössbauer effect experiments have been done on trans-[Fe(diars)2Cl2]·(BF4)2 in the presence of magnetic fields up to 53 kOe and in temperatures ranging from 4.2 to 348°K. The data have been interpreted in terms of spin Hamiltonian parameters with an effective spin S=1. These parameters in turn have led to a determination of the ligand field which acts on the t2g4 configuration as well as the spin-orbit coupling.
Dissociation Energy of CuCl and Cu2Cl2 Gaseous Molecules
Authors: Guido M. , Gigli G. , Balducci G.
Published: February 2004

Using the mass spectrometric and double oven technique, the molecules CuCl(g) and Cu2Cl2(g) have been observed in the superheated vapors of cuprous chloride. From the study of the various gaseous equilibria, the atomization energies of CuCl(g) and Cu2Cl2(g), D0o(CuCl)=90.6± 1.1 and D0o(Cu2Cl2=225.8± 1.1 kcal/mole, were derived. Polymerization energies of CuCl to dimer, trimer and tetramer, and the energy of formation of Cu2Cl2(g) from trimer and tetramer were also determined.