bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical study of the electronic structure of ferrocene and ferricinium: Application to Mössbauer isomer shifts, ionization potentials, and conformation
Authors: Bagus P. S. , Walgren U. I. , Almlof J.
Published: February 2003

Self-consistent field wavefunctions have been obtained for ferrocene and several low-lying states of the ferricinium ion using extended basis sets of contracted Gaussian functions. In agreement with the near minimal basis set results of Coutière et al., the electronic structure is found to change very considerably when ferricinium is formed by removing an electron from an Fe d molecular orbital of ferrocene. The ionicity of Fe, as determined by a Mulliken gross population analysis, is found to be +1.47 for the ion and +1.39 for ferrocene. The difference is less than 0.1 electrons, while a value close to one would have been expected. The major contribution to the change in structure comes from a greatly increased covalency of the ligand orbitals of e1g symmetry in the ion. The change is shown to be responsible for the small differences found between the isomer shifts, and thus electron densities at the Fe nucleus, in ferrocene and ferricinium salts. Direct contributions from Fe 4s electrons are found to account for about half of the 0.93a−30 difference in the electron density. A value of the change in nuclear radius, δR/R=−4.4×10−4, is estimated from the computed densities. Computed values of the six lowest ionization potentials of ferrocene are compared with photoelectron spectra, and symmetry assignments of the ionic levels are made. The average error of the computed ionization potentials is 0.5 eV, giving confidence to these assignments. For the states considered, wavefunctions have been obtained for both the eclipsed and staggered conformations of the C5H5 rings. Both absolute and relative total energies are found to be essentially the same for either conformation.
The determination of optical absorption intensities using the Xα scattered wave method
Authors: Noodleman L.
Published: February 2003

A density matrix formulation for optical absorption is developed within the Xα scattered wave theory using the transition state concept. Oscillator strengths for optical excitations in H+2, H2, and FeCl4−1 are given for the f (∇V) form. In H+2, oscillator strengths accurate to about 10% are found for R?2.0 a0 (the equilibrium nuclear separation). In H2, the intensity of the X 1Σg→B 1Σu transition at equilibrium is very accurately described (error ? 10%), but the X 1Σg→C 1Πu transition intensity is not satisfactory due to the diffuse character of the 1Πu state. The errors in the H2 and H+2 intensities are associated with specific defects in the scattered wave model. These defects should not, however, cause significant errors in many systems of chemical interest. Consistent with this viewpoint, semiquantitative agreement is found between the theoretical and experimental intensities in FeCl4−1.
Studies in fluctuation analysis: I. On relations between rate constants and relaxation times in chemical systems and the multivariate power spectrum of noise and fluctuations
Authors: Romine William O.
Published: February 2003

An investigation of the stochastic fluctuations that occur in chemically reactive solutions is presented in terms of irreversible chemical thermodynamics. The approach considers in some detail the properties of the fluctuations in the frequency domain (e.g., the power spectrum) and it is found that (1) the kinetic rate constants of the reaction process can be obtained directly from the inverse of the normalized power spectrum extrapolated to the zero frequency point, (2) the Onsager flow coefficients are derived from the second moments and the inverse of the power spectrum at the zero frequency extrapolation, and (3) the eigenvalues of the normalized spectrum are the chemical relaxation times. It is suggested that the approach outlined in this article may prove useful in studies of chemical kinetics without the necessity of resorting to macroscopic relaxation methods.
Raman spectrum of ice VIII
Authors: Wong P. T. T. , Whalley E.
Published: February 2003

The Raman spectra of H2O and D2O ice VIII recovered at ∼100 K and zero pressure have been measured in the range 4000–50 cm−1. The three stretching, three rotational, and four translational bands expected from the symmetry of the crystal have been identified. Two bending bands are expected and have been tentatively identified among some weak bands. The relative intensity of the rotational and stretching bands is much smaller than in the vapor, and so if the intensity of the stretching bands is not greatly changed, the anisotropy of the polarizability is appreciably smaller in ice VIII than in the vapor.
The criterion of minimum state density in unimolecular rate theory. An application to ethane dissociation
Authors: Hase William L.
Published: February 2003

The application of the criterion of minimum state density is described and a model potential energy function is determined for ethane dissociation. Comparisons are made between thermal rate constants calculated using the RRKM and activated complex theories. Activated complex structures are chosen by a Boltzmann average of the minimum state density criterion.
Calculation of adiabatic radial and angular-momentum matrix elements using variational wavefunctions for H2+
Authors: Schinke R. , Krüger H.
Published: February 2003

Several adiabatic energy curves and wavefunctions for H2+ are calculated using a variational treatment. The agreement with exact adiabatic energies is excellent. Further, these variational wavefunctions are used to evaluate the radial matrix elements 〈α‖d/dR‖β〉 and the angular-momentum matrix elements 〈α‖iLy‖β〉 which are needed for treating atom–atom collisions by use of expansions in molecular states.
Spectroscopy of the CsH (X 1Σ+) state by laser-excited fluorescence
Authors: Tam A. C. , Happer W.
Published: February 2003

Using the technique of laser-excited fluorescence, the ground state vibrational levels of CsH molecules are observed up to v″=14, corresponding to 60% of the dissociation energy from the lowest vibrational level. The highest vibrational levels previously observed (Almy and Rassweiler) have v″=2. A polynomial fit to the Birge–Sponer plot of the present data yields the following parameters for the ground state term values (in cm−1): ωe=891.0(4), xeωe=12.93(11), yeωe= 0.105(13) and zeωe=−0.00178(45). The extrapolation of the fit gives the ground state dissociation energy D0 as 2.08(6) eV.
Quantum theory of angular momentum coupling in reactive collisions
Authors: Schulten Klaus , Gordon Roy G.
Published: February 2003

Quantum scattering theories of chemical reaction usually require, at some stage, a transformation from the quantum states of reactants to those of the products. We show that it is useful to separate this transformation into angular momentum coefficients and translational–vibrational integrals. The angular momentum coefficients thus defined are general kinematic factors, depending only on the masses of the atoms and the product vibrational and translational distances, but not on the particular potential surface. Analytic formulas are derived for these angular momentum coefficients, both for reactions confined to a plane and for three-dimensional motion. Various selection rules, symmetry properties, orthogonality conditions, normalization rules, and recursion relations are derived from these formulas. An efficient and numerically stable method is derived for numerical evaluation of the angular momentum coefficients. Examples are given for several specific reactions and the trends with varying mass combinations are rationalized in terms of limiting cases. These results display the kinematic aspects of angular momentum transfer in chemical reactions. Comparison with classical trajectories, which include both dynamic and kinematic effects, shows the extent to which dynamic effects alter the distributions of rotational and orbital angular momenta from those given by the kinematic effects alone. Finally, the integral for the transformation of the vibrational and radial dependence of the scattering wavefunction is discussed qualitatively.
Transition moments for the B 3Σ−u–X 3Σ−g and 3Πu–X 3Σ−g transitions in O2
Authors: Julienne P. S. , Neumann D. , Krauss M.
Published: February 2003

Multiconfiguration self-consistent field wavefunctions are used to calculate the transition moments for the two lowest dipole allowed transitions in O2. The transition matrix element for the B–X transition calculated at Re of the ground state corresponds to an oscillator strength of 0.18, in good agreement with the experimental integrated oscillator strength 0.16 of the Schumann–Runge continuum. The B–X transition moment is calculated as a function of internuclear separation. The transition matrix element to the repulsive valence 3Πu state calculated at Re of the ground state corresponds to an oscillator strength of 0.003. Although the weak 3Πu absorption continuum is masked by the strong Schumann–Runge continuum below 1750 Å, this 3Πu absorption may contribute to the background continuum in the Schumann–Runge band region at low temperature.
Vibronic symmetry correlation in molecular combination and dissociation
Authors: Chiu Ying-Nan
Published: February 2003

The principle of conservation of vibronic symmetry in molecular combination and dissociation is discussed. It leads to the aufbau of the vibronic (vs purely electronic) states of polyatomic molecules. Methods to construct composite vibrational (and vibronic) wavefunctions from those of molecular fragments (reactants or products or transition complexes) are described. These vibronic functions, constructed from local site symmetry, will have the overall symmetry of the point group that is preserved throughout the reaction and will possess the correct dissociation limit. The construction of a composite vibrational wavefunction is illustrated by using a symmetrically and collinearly dissociating X2Y2 molecule. The theory of vibronic correlation is applied to the recently observed production of excited formaldehyde (and its chemiluminescence) from the reaction of O2(1Δg) with olefins. This theory promises one a qualitative way to conceive the possible vibronic excitation of reactants and products in a chemical reaction.
Translational energy distribution of the unimolecular HX(X=F,Cl) elimination reactions
Authors: Kim K. C.
Published: February 2003

The translational energy distribution from the metastable of the C2H3F+ ion has been obtained using a new model of metastable peak shape simulation. This transition represents a class of the unimolecular HX(X=F,Cl) elimination reactions in terms of the energy partitioning pattern. However, it is unique in that the fractional translational energy release is 0.69±10% based on an estimate of the total available energy. The energy distribution is characterized by an average energy of 0.95 eV (±5%) with a half-width of ∼0.2 eV. The origin of the translational energy is discussed in terms of a four-centered transition model on a repulsive potential surface in the exit channel. Comparisons are made between the metastable reaction of the C2H3F+ ion and similar neutral reactions.
The FS correlation and a systematic analysis of the stretching absorptions of water in the condensed state
Authors: Schiffer J. , Intenzo M. , Hayward P. , Calabrese C.
Published: February 2003

The separation between uncoupled ν3 and ν1 frequencies of water symmetrically bound in both nonaqueous solvents and hydrates has been shown to vary linearly with the HOD stretching frequency of water, for both H2O and D2O. This relation, the FS correlation, has been explored theoretically and it has been shown to be useful for estimating geometry changes of water in hydrates, upon deuteration. It is also useful in determining the effect of cation coordination on the stretching frequencies of water molecules. A method is also developed, using this relation, for systematically analyzing the origin of the stretching bands of water in condensed systems.
Sulfur LII,III emission spectra and molecular orbital studies of sulfur compounds
Authors: Taniguchi Kazuo , Henke Burton L.
Published: February 2003

The fluorescent sulfur LII,III emission spectra have been quantitatively measured and analyzed for the relative strengths (radiative yields) of the allowed transitions, and for the corresponding emission linewidths. These were investigated for the sulfur compounds in the solid, vapor, and gas states—Na2SO4, K2SO4, CdSO4, Na2SO3, K2SO3, C4H4S, H2S, SO2, and SF6. The S LII,III spectra for the solid compounds (all strongly ionic) revealed essentially the same localized molecular orbital character about a central sulfur atom as for the molecular compounds—showing no significant influence of the cations and no evidence of crystal band structure. The measured molecular orbital energies and radiative yields were found to be generally consistent with the eigenvalue and eigenvector calculations based upon current CNDO and ab initio molecular orbital approximation methods. The measured sulfur LII,III spectra for the compounds reported in this paper have been interpreted according to the valence orbital configuration as obtained from the CNDO/2 method. This is done while recognizing that other reported molecular orbital calculations on these molecules often indicate different orderings. The molecular orbital energies as derived from the LII,III spectra have also been compared with those obtained from photoelectron spectroscopy, demonstrating, generally, very good agreement between these two methods. Because the LII,III spectra for second row elements probe the 3s and the 3d character of the valence band and the Kβ spectra probe the 3p character of the valence band, it has been found very useful to combine the results of these x-ray emission techniques in order to gain a complete analysis of valence band electronic populations and symmetries. It has been shown that the LII,III emission analysis can be a uniquely powerful tool for the determination of the role of the 3d atomic orbital in the chemical bonding of the second-row elements.
Dipole moment derivatives and infrared intensities. II. Polar tensors in methyl halide molecules
Authors: Newton James H. , Person Willis B.
Published: February 2003

Atomic polar tensors have been determined for H, C, and X atoms of the methyl halide molecules (CH3X), using infrared intensity data reported by Russell, Needham, and Overend. The signs for the ∂p/∂Qi’s have been chosen by considering Coriolis coupling constants, agreement between intensity parameter values for CH3X and CD3X, and by considering the values of the atomic polar tensors calculated by CNDO methods for CH3F and CH3Cl. The resulting atomic polar tensors show systematic trends for the CH3X molecules as X change from F to I. The possibility that atomic polar tensors can be transferred from one molecule to another (with some allowance for expected trends) cannot be ignored. Atomic effective charges for each atom have been calculated, and ξH is found to be nearly constant for the four molecules. Additional properties of the atomic polar tensor are examined, including the anisotropy. A ''modified bond moment hypothesis'' appears to be reasonably successful in modeling the infrared intensities of the methyl halides.
On the use of high energy approximations to calculate intensities and angular distributions in atomic or molecular photoelectron spectroscopy
Authors: Ritchie Burke
Published: February 2003

We examine the forms asymptotic in the energy for the differential and integral cross sections for ejection of photoelectrons from atomic or molecular targets. We find the plane wave, length form to be in disagreement with the plane wave, velocity form and the Coulombic, length form at all energies, and the plane wave, velocity form to be in disagreement with the Coulombic, length form at all energies except in the case of photoejection from the 1s orbital. Agreement of the plane wave, velocity form with the Coulombic, length form for initial orbitals of higher angular momentum can be produced by use of the first Born correction to the plane wave due to the presence of the Coulomb potential. It is demonstrated that orthogonalization of the plane wave to other bound orbitals of the system gives a result which will agree with the Coulombic, length and corrected plane wave, velocity forms only for particular values of the screening parameters of these orbitals, demonstrating that orthogonalization of the plane wave cannot lead to correct asymptotic forms except by accident. We discuss the method used to eliminate the divergences in the first Born correction to the electric-dipole amplitude due to the infinite range of the Coulomb potential by interchange of the order of integration over coordinate space in the amplitude with the integration over momentum space in the Fourier representation of the wavefunction.
Upper and lower bounds of two- and three-body dipole, quadrupole, and octupole van der Waals coefficients for hydrogen, noble gas, and alkali atom interactions
Authors: Tang K. T. , Norbeck J. M. , Certain P. R.
Published: February 2003

Upper and lower bounds of the multipole van der Waals coefficients C6, C8, and C10 for hydrogen, noble gas, and alkali atoms are established. Nonadditive three-body coefficients involving dipole, quadrupole, and octupole interactions are also determined. For the dipole polarizabilities a three-term, two-point Padé approximant is used to obtain the upper bound and a two-term Padé approximant is used to obtain the lower bound. For the quadrupole and octupole polarizabilities a one-term approximation of the dynamic polarizability is used, except for the helium quadrupole polarizability, where extended approximations are possible.
An exact quantum mechanical treatment of charge transfer at low energies for the H++H2 reactive collinear system
Authors: Top Z. H. , Baer M.
Published: February 2003

Quantum mechanical calculations for the reactive charge transfer collinear system H++H2(v) are reported. (AIP)
Beryllium borohydride: C3v or D3d ?
Authors: Marynick Dennis S.
Published: February 2003

A b initio self-consistent field calculations with a double zeta basis set have been performed on two previously suggested structures for gas phase beryllium borohydride. It is demonstrated that one of the structures (of C3v symmetry) does not represent a minimum on the SCF energy surface. The implications of this result are briefly discussed.
Vibrational spectroscopy of matrix-isolated UF6 and UF5
Authors: Paine Robert T. , McDowell Robin S. , Asprey Larned B. , Jones Llewellyn H.
Published: February 2003

The vibrational spectrum of UF6 molecules isolated in Ar, Xe, and CO matrices is reported. Also, the ir spectrum of monomeric UF5 molecules produced in these matrices by photolysics with uv radiation is reported. (AIP)
A new approach to time-dependent perturbation theory
Authors: Mehrotra Suresh C. , Boggs James E.
Published: February 2003

A time-dependent perturbation theory for the solution of the time-dependent Schrödinger equation is developed and is applied to systems having two states with pulse and Lorentzian types of perturbations. It is shown in the case of the pulse perturbation that the expression corresponding to the Nth order of the perturbation theory converges to the exact solution when N tends to infinity. The results obtained from this perturbation theory, the Magnus approximation, and the time-dependent perturbation theory developed by Dirac are compared with the exact results. This theory is found to be good for larger values of the perturbations and for larger intervals of time.
Large perturbations and nonexponential decays in spin relaxation. Applications of the memory function theory
Authors: Anderson Charles F. , Hwang Lian-Pin , Friedman Harold L.
Published: February 2003

Our memory function theory of time correlation functions [J. Chem. Phys. 62, 2098 (1975)] is applied to two problems which are met in the theory of proton relaxation in aqueous solutions of Ni++. In this system the modulation of the zero-field splitting (zfs) which drives the electron spin relaxation is neither small enough nor fast enough for the usual second-order perturbation calculation to be accurate or for the relaxation to obey Bloch’s equations. Here the perturbation series for the memory function is rearranged to give a new series which converges rapidly even when the perturbation is large. This result is exact for a particular model for the modulation process and for vanishing external magnetic field. It is applicable as an approximation method more generally. When the Solomon–Bloembergen equations are used to calculate the relaxation rates of the protons due to interaction with the electron spins, and the latter do not obey Bloch’s equations, then we show how the electron spin relaxation times and Larmor frequency are to be replaced by ’’effective’’ parameters which now depend upon the modulation of the proton–electron spin interaction as well as on the field and the parameters of the zfs interaction. Finally, calculations for proton relaxation rates based on the new theory are compared with those done in a standard way for the case of interest.
Chemical pumping of the water vapor laser. I
Authors: Downey Gale D. , Robinson Dean W.
Published: February 2003

Flash photolysis of mixtures of O2/H2O/O3 leads to lasing at 357.53 cm−1. Emission at this wavenumber coincides with that of the strongest line that is observed from both the pulsed and cw water vapor discharge laser. Accordingly it is assigned to the (001)633– (020)550 transition in water. The pumping scheme O3→hνO(1D)+O2(1Δg), (1); O(1D)+O2(3Σ−g) →O2(1Σ+g)+O(3P), (2); O2(1Σ+g)+H2O→O2(1Δg)+H2O†, (3), where H2O† subsequently lases, is consistent with all the experimental observations. Computer modeling of this sequence of reactions reproduces both the observed pulse’s profile and its onset delay after flash initiation.
Hydrostatic equilibrium in fluid interfaces
Authors: Toxvaerd So/ren
Published: February 2003

The statistical mechanical expression for the pressure tensor is used to determine the density distribution in a fluid interface in hydrostatic equilibrium. The two principal assumptions in the model are, firstly, that an expansion of the pair distribution function in the interfacial gradient converges so rapidly that only the zero and first order terms are necessary to determine the density profile, and, secondly, that the radial distribution function for particles in an isochore plane can be obtained from the continuation of the bulk radial distribution function into interfacial densities. The resulting monotonic density functions agree well with otherwise obtained functions. It is tested whether the equation for hydrostatic equilibrium, in the present formulation gives, as it should do, the same interfacial density profiles as the first integrodifferential equation in the Born–Green–Yvon–Bogolyubov hierarchy.
Intensities of vibrational difference bands
Authors: Overend John
Published: February 2003

It is shown that the intensity of a binary difference band in the vibrational spectrum of a polyatomic molecule is not necessarily related in any simple way to the intensity of the corresponding binary combination band. The effects of mechanical anharmonicity on the matrix elements 〈vs,vs′‖P‖vs+1,vs′+1 〉 and 〈vs,vs′+1‖P‖vs+1,vs′ 〉 are quite different and hence the relative intensities of the difference and combination bands are complex functions of the anharmonic force constants and the dipole-moment derivatives. For this reason it is possible to find extraordinary resonance enhancements of the transition probability in difference transitions which have no counterpart in the combination transitions.
Studies on the charge transfer spectrum of Co++ in KCl
Authors: Trutia Ath. , Vodă M.
Published: February 2003

Systematic experimental measurements have been carried out on the crystal field and charge transfer spectra for divalent cobalt ions in a series of alkali halide crystals. The influence of divalent lead ions on these spectra has also been investigated. Additionally, the spectrum of Co++ in acetone with LiCl has been studied and the charge transfer band is found to be absent. The analysis of these measurements and earlier data indicate that the interstitial model for the cobalt complex in KCl proposed in the literature is unsatisfactory. An alternate model involving regions in which double salts (such as M2CoCl4) are present is shown to successfully explain the available data.
The interaction of ions with nonpolar neutrals: The collision broadening of ion cyclotron resonance lines of ions in hydrogen and methane
Authors: Ridge D. P. , Beauchamp J. L.
Published: February 2003

The motion of ions in an ion cyclotron resonance cell is considered, and measurements of ion cyclotron resonance linewidths are described. The connection between cyclotron resonance linewidths and kinetic parameters is developed. Mobilities and collision frequencies of CH5+, C2H5+, C3H7+, C4H9+, and Na+ in methane and H+, H3+, H30+, CH5+, C2H5+, C3H7+, and Na+ in hydrogen are determined from the linewidth measurements. Resulting mobilities of H+, H3+, and Na+ in H2 are found to agree well with drift tube measurements, in contrast to previous cyclotron resonance linewidth determinations. The mobilities are interpreted in terms of three model ion molecule interaction potentials. The mobilities are found to be in general consistent with both a three term 12–6–4 potential and an acentric potential but not with the simple polarization potential. Potential parameters consistent with binding energies from the literature and the present mobility measurements are reported for H3+–H2, CH5+–CH4, and C2H5+–CH4.
Nonrandomization of energy at high pressures in photochemical systems
Authors: Oref I.
Published: February 2003

A general mechanism which explains the effects of high pressures on photochemically induced unimolecular reactions is proposed. As an example, the photochemically induced unimolecular decomposition of cycloheptatriene is discussed in great detail. It is shown that if both random and nonrandom channels for decomposition are postulated, the caluclated results show the leveling off behavior found in the experimental Stern–Volmer plot.
Theoretical study of the binding of an electron to a molecular dipole: LiCl−
Authors: Jordan K. D. , Luken W.
Published: February 2003

Ab initio calculations are carried out to determine the nature of the binding of the LiCl anion. The extra electron.is found to be in a predominantly nonbonding orbital on the lithium end of the molecule and the calculations predict an electron affinityu of LiCl of 0.54 eV. This is in good agreement with the experimental value of 0.61 eV, which has been recently determined by Carlsten, Peterson, and Lineberger. The ab initio results are discussed in light of the finite dipole model.
An eigenfunction expansion method for the analysis of exponential decay curves
Authors: Provencher S. W.
Published: February 2003

A method is developed for the analysis of data composed of random noise, plus an unknown constant ’’baseline,’’ plus a sum (or an integral over a continuous distribution) of exponential decay functions. It is based on the expansion of the solution of a Fredholm integral equation of the first kind in the eigenfunctions of the kernel. In contrast to the Fourier transform solution [Gardner et al., J. Chem. Phys. 31, 978 (1959)], the finite time range of the data is exactly accounted for, and no extrapolation or iteration is necessary. A computer program is available for the analysis of sums of exponentials. It is completely automatic in that the only input are the data (not necessarily in equal intervals of time); no potentially biased initial estimates of either the number or values of the amplitudes and decay constants are needed. These parameters and their standard deviations are decided with a linear hypothesis test corrected approximately for nonlinearity. Tests with simulated two-, three-, and four-component data containing pseudorandom errors indicate that the method has a wide range of applicability.
A note on semiclassical bound states and correspondence principles
Authors: McLafferty Francis J. , George Thomas F.
Published: February 2003

Semiclassical bound state theory is considered from the viewpoint of the phase space representations of quantum mechanics. In the small h/ limit, within a representation defined by the ordering chosen for the noncommuting position and momentum operators, we obtain: (1) equations of motion, which need not be classical and (2) correspondence principles in action-angle variables, regarded as those initial conditions on the equations of motion which dominate in the small h/ limit. The Weyl ordering is seen to generate the classical equations of motion and the normal correspondence result. Possible evaluation of semiclassical bound state energies is discussed by means of the eigenvalue approach to classical mechanics used by Prigogine and co-workers.
The magnetic hyperfine interaction of iron monomers and dimers isolated in an argon matrix
Authors: Montano P. A. , Barrett P. H. , Shanfield Z.
Published: February 2003

The Mössbauer effect has been used to measure the magnetic hyperfine interaction of isolated iron monomers and dimers in solid argon with an applied external magnetic field. For an applied external field of 30 kOe an internal magnetic field at the 57Fe nucleus for the iron monomer of 830±15 kOe was observed (external field included). The internal field at the 57Fe nucleus in the iron dimer is 660±5 kOe with a negative Vzz(eQVzz<0). The large internal field at the 57Fe nucleus in the iron dimer indicates that the ground state of the Fe2 molecule has a large angular momentum. Also observed was a six-line spectrum with an internal field of 442±8 kOe and isomer shift of 0.50±0.06 mm/sec. This spectrum is attributed to the presence of molecules or clusters of FeO.
Dynamics of stiff polymer chains. IV. High frequency viscosity limit
Authors: Fixman M. , Evans G. T.
Published: February 2003

The limiting high frequency intrinsic viscosity [η]∞ has been calculated for several models of a freely rotating chain, with and without hydrodynamic interaction. The calculated values of [η]∞ lie far below the experimental values. This indicates that the dominant contribution to [η]∞ does not originate in bond tensions.
Nuclear magnetic resonance of ferroelectric NaNH4C4H4O6⋅4H2O and NaND4C4H2D2O6⋅4D2O
Authors: El Saffar Z. M. , Peterson E. M.
Published: February 2003

Deuteron NMR spectra, and proton and deuteron spin–lattice relaxation times have been studied on both sides of the paraelectric–ferroelectric transition in ammonium Rochelle salt, NaNH4C4H4O6⋅4H2O. Complete rotation patterns obtained near 300 K for the deuteron resonance of D2O are successfully interpreted in terms of the crystal structure of ordinary Rochelle salt with the assumption that all four D2O molecules are undergoing 180° flip motion. The deuteron resonance spectra of ND+4 are attributed to rapidly reorienting and distorted ND+4 tetrahedra which undergo a radical change at the Curie temperature (122 K) indicating the onset of a first order phase transition. The spontaneous polarization computed from the distortion of ND+4 determined by NMR accounts for 52% of the total polarization of ARS. Proton and deuteron relaxation times are interpreted in terms of a relatively fast reorientation of the NH+4 tetrahedra about their twofold axes accompanied by a relatively slow reorientation about their threefold axes. Below about 130 K the threefold motion becomes ineffective in producing relaxation, but the deuteron resonance line splittings remain relatively small down to 77 K, the lowest temperature of measurement. No deuteron resonance spectra typical of ND+4 tetrahedra rotating about their twofold axes were observed, probably because of the presence of quantum mechanical tunneling.
Isotope chemistry and molecular structure. Carbon and oxygen isotope chemistry
Authors: Bigeleisen Jacob , Hom Richard C. , Ishida Takanobu
Published: February 2003

The relationships between force constants and the isotope chemistry of carbon and oxygen are calculated for H2O, CO2, CH2O, CH4, C2H4, C2H6, and C6H6. Significant differences are found from the general features of protium–deuterium isotope chemistry. These are shown to be associated with a structural effect. Hydrogen is always an end atom except for hydrogen bonded moleules. Carbon is generally tetrahedrally bonded and its isotope chemistry shows significant contributions from the interaction between stretching and bending modes. These interactions lead to deviations in additivity of the total isotope effect from the contributions of the individual force constants. Stretching forces dominate the isotope chemistry of carbon and oxygen as they do in hydrogen. They account for 70%–90% of the reduced partition function ratios. Correlations are made between the stretching force contributions and molecular structure. It is shown that while significant differences exist between the specific contributions calculated from different force fields for methane, ethane, and benzene, the absolute value of ln(s/s′) f is rather insensitive to the detailed structures of the F matrices studied.
An experimental and theoretical study of the Auger spectrum of nitrous oxide
Authors: Connor J. A. , Hillier I. H. , Kendrick J. , Barber M. , Barrie A.
Published: February 2003

The oxygen and nitrogen K–LL Auger spectra of N2O are reported and interpreted by means of configuration interaction calculations of the various states of N2O2+. The charge distributions in the three core hole states of N2O have been calculated by the restricted Hartree–Fock method and used in estimates of the relative intensities of the Auger transitions. Such estimates, together with the calculated energies of the different states of N2O2+, allow an assignment of the reported Auger spectra to be made.
Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. I. Heat capacity, entropy, magnetic moment from 0.5 to 4.2 °K with fields to 90 kG along the c crystal axis
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2003

The heat capacity of a 3.920 cm diam spherical single crystal of neodymium ethyl sulfate hydrate has been measured with stabilized fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the c crystal axis, from 0.5 to 4.2 °K. The zero of electronic entropy was reached at 90, 65, and 40 kG and the lower temperatures. Corrections were applied for the nuclear polarization of the protons and the neodymium isotopes 143 and 145. The isoerstedic entropy changes derived from the heat capacity series were interconnected by 29 series of temperatures on ’’adiabatics,’’ corrected to isentropes. The lattice heat capacity in the liquid helium range can be represented by Clat= (1.44±0.01) ×10−3 T3 gibbs/mole NES. The magnetic moment was measured over the same field and temperature ranges used for the heat capacities plus magnetic moments at 500 and 1500 G. The saturation limit of the temperature-dependent magnetic system was 10 036 G⋅cm3/mole NES, corresponding to gc=3.594. A temperature-independent magnetic susceptibility was found to be 0.00341 cm3/mole NES. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5–4.2 °K. These data will be used as a starting reference for investigating the properties of NES in the region below 0.5 °K. Comparison of the magnetic moment and heat capacity data with an ionic crystal field model plus a dipolar molecular field, using derived parameters, leads to general good agreement.
The thermal diffusion factor and interatomic potential for xenon
Authors: Taylor W. L.
Published: February 2003

The isotopic thermal diffusion factor of xenon was measured from 187 to 850 K in a 20-tube trennschaukel. The results are consistently about 40% lower than the data of Paul, Howard, and Watson. A comprehensive comparison of proposed interatomic potentials for xenon was made with the experimental data obtained. The ’’extended’’ corresponding states reduced thermal diffusion factors were calculated and compared to a composite of the present data and reduced thermal diffusion factors for Ne, Ar, and Kr obtained in previous work. The composite data were found to be consistent with second virial coefficients and other transport properties for the noble gases. A method is given for improving the order of approximation of the reduced thermal diffusion factors obtained from the ’’extended’’ corresponding states theory.
Electron paramagnetic resonance in nickel fluotitanate
Authors: Rubins R. S. , Griffin Bobby C. , Burris Rick
Published: February 2003

EPR in single crystals of NiTiF6⋅6H2O has been studied in the frequency ranges 12–18 GHz and 23–25 GHz. A phase transition from the room temperature trigonal structure to a lower symmetry structure takes place at a temperature between 134 and 137 °K for a slowly cooled sample. The reverse transition occurs at approximately 141 °K. As the phase transition takes of the order of 10 min for completion, the trigonal phase may be retained at low temperatures by rapidly cooling the sample below about 100 °K. In the trigonal phase above 4.2 °K, both g∥ and g⊥ are approximately 2.27 and the crystal field parameter D has the magnitude (1.30±0.01) cm−1 at 4.2 °K, (1.337±0.005) cm−1 at 77 °K, and (1.31±0.01) cm−1 at 298 °K. The data for the trigonal phase below 4.2 °K may be represented by divergent g values, with g∥?2.50 and g⊥?2.20 at 1.3 °K. In the low symmetry phase, with g∥ assumed to be 2.25, the crystal field parameters at 77 °K are ‖D‖?2.0 cm−1 and ‖E‖?0.20 cm−1.
Adsorption of Ar on a nonuniform MgO surface
Authors: Hinman David C. , Halsey G. D.
Published: February 2003

Data are presented for the adsorption of Ar and N2 on a strongly heterogeneous MgO surface at 84 °K and for Ar at a range of temperatures between 130 and 250 °K. The high-temperature data are analyzed according to a model which separates the contributions to the potential into bulk and surface terms, providing a method for the determination of the surface area from parameters characteristic of the bulk material. A solid–gas energy parameter and parameters indicating the strength of the impurity sites are also evaluated.
A new Monte Carlo method for calculating surface tension
Authors: Miyazaki J. , Barker J. A. , Pound G. M.
Published: February 2003

A new Monte Carlo method for calculating the surface tension of a liquid is described. The method is based on a direct evaluation of the free energy required to create a surface, unlike earlier Monte Carlo calculations which evaluated the surface stress. It is applied to the 6:12 fluid in conditions close to the triple point for argon. The calculated surface tension agrees within statistical uncertainty with previous Monte Carlo estimates, but the statistical uncertainty of the present method is much lower. Agreement with experimental data for argon is not good, as should be expected; estimates of the effects of using a correct pair potential and particularly of including three-body interactions indicate that they would lead to good agreement.
Relaxation of polar cylinders in strong electric fields
Authors: Oh Byung K. , Labes M. M. , Salomon R. E.
Published: February 2003

The problem of rotational diffusion of a polar cylinder about its long axis in an electric field has been solved. The solutions apply to the high as well as the low field limits. The results are presented as a function of a reduced time and the variable κ, which is a measure of the ratio of mean electrical energy to thermal energy. Asymptotic expansions are obtained for the distribution function and the fractional polarization. The eigenvalues and even solution of a Whittaker–Hill–Ince differential equation have been calculated as functions of κ. Asymptotic expansions of the eigenvalue and solution of this equation are given.
Electron spin resonance of electron irradiated Ni(CN)4K2 in KCl
Authors: Zanette S. I. , Caride A. O. , Danon J.
Published: February 2003

Single crystals of KCl doped with Ni(CN)4K2 0.02M were irradiated with 2 MeV electrons. ESR studies of the samples with 70% of 13C reveal the existence of four species assigned to be [Ni(CN)4Cl2]3− and [Ni(CN)4Cl2]5− in the isomeric states cis and trans. The form of the g and A tensors is discussed, and it indicates that the great anisotropies observed in the cis species are due to the influence of the vacancy created by charge compensation.
Electronic states and molecular constants of Bi2
Authors: Gerber G. , Broida H. P.
Published: February 2003

Potential energy curves of several electronic states of Bi2 have been calculated by the Rydberg–Klein–Rees method using molecular constants obtained from laser-excited photoluminescence of Bi2. These potential curves are used to compute Franck–Condon factors. Franck–Condon factors for the A–X system are compared with measured intensities of photoluminescence series extending over 50 vibrational levels (v″= 0–49) and including both Franck–Condon maxima. It is shown that more accurate molecular constants can be derived by using the information contained in these intensity data. Another important result is achieved by deriving previously unknown vibrational and rotational constants of the upper electronic state of the E–B doublet photoluminescence series using only line intensity measurements. Relative energy positions of the electronic states have been obtained by perturbation considerations and by measuring the temperature dependent changes of relative intensities of photoluminescence lines belonging to different electronic transitions. These experiments suggest that there is an electronic state X ′, which is lower in energy than the X state. A potential energy diagram for Bi2 is derived including the re-evaluated published spectroscopic data of Bi2.
Two approaches to the description of solvent effects upon some NMR properties observed on highly concentrated polymer systems
Authors: Cohen-Addad J. P.
Published: February 2003

Two approaches are proposed to calculate the nonzero average dipolar spin coupling strength observed on highly concentrated polymer solutions. One is based on the current particle path picture. The model of polymerized solids of Edwards and Kerr is used to predict the approximate dependence of the nonzero average dipolar spin coupling upon entanglements and cross links. The other approach is based on the effect of the probability distribution of monomer unit pairs. The lattice treatment of solvent polymer mixtures proposed by Guggenheim is used to predict the dependence of the dipolar coupling strength upon the temperature and the solvent concentration. This dependence is compared with recent experimental results obtained from high resolution proton spectra of polyisobutylene chains. It is shown to be in good agreement with the observed dependence. Accordingly, the free energy of mixing of the solvent–monomer unit is considered as available from proton high resolution spectra of highly concentrated polymer solutions. The two approaches are supposed to hold only when polymer chains are completely mixed with each other.
Hydrogen abstraction reactions by atomic fluorine. V. Time-independent nonthermal rate constants for the 18F+H2 and 18F+D2 reactions
Authors: Feng Da-Fei , Grant Edward R. , Root John W.
Published: February 2003

The general time-independent collision theory formulation for the bimolecular rate constant has been adapted for the description of hot atom systems. Two types of hot atom energy distribution functions have been considered in an application to the 18F+H2 reaction system: (i) a δ-function distribution, and (ii) a steady-state Maxwellian distribution characterized by a hot atom temperature TA. From the time-independent solution of the Boltzmann equation together with microscopic reactive cross sections determined from quasiclassical trajectory computations, nonthermal 18F+D2 processes. The results showed little sensitivity to the assumed shape of the hot atom energy distribution or to the magnitude of the barrier height along the reaction coordinate. The intermolecular kinetic isotope effect κH2/κD2 provided a sensitive probe of the average energy of hot reaction, suggesting an average 18F laboratory kinetic energy of 50±10 eV for the 18F+H2 process under nuclear recoil conditions.
A study of electronically excited nitrogen dioxide in its first predissociation region: Fluorescence emission, lifetimes, and electronic quenching
Authors: Uselman William M. , Lee Edward K. C.
Published: February 2003

Fluorescence behavior of NO2 in the first predissociation region (3979 to 4200 Å) was studied in great detail with fluorescence excitation spectroscopy (FEX) and the phase-shift technique. The fluorescence quantum yield decreases with increasing pressure due to self-quenching but the shape of the excitation spectrum is insensitive to pressure variation. The observed fluorescence decay time is independent of exciting wavelength from 3979 to 4200 Å, although it becomes shorter at higher pressures. These observations imply the presence of a fluorescing species with a constant intrinsic lifetime of ∼7×10−5 sec and a predissociating species with a very short lifetime (<10−7 sec) which does not show collisional fluorescence stabilization at ordinary pressures. Bimolecular electronic self-quenching constants have been determined in the predissociation region to be ∼4×10−11 cm3 molecule−1⋅sec−1. Rotationally hot molecules can predissociate, although their photon energy contents are less than the dissociation threshold energy of 25 105 cm−1, by releasing the original rotational energy to the ’’bond-breaking’’ vibration. The predissociation limit determined by fluorescence excitation spectroscopy is ∼3980 Å, very close to the previously determined value of 3979 Å by absorption line diffuseness [A. E. Douglas and K. P. Huber, Can. J. Phys. 43, 74 (1965)].
ESR line shape studies of trapped electrons in γ-irradiated 17O enriched 10M NaOH alkaline ice glass: Model for the geometrical structure of the trapped electron
Authors: Schlick S. , Narayana P. A. , Kevan Larry
Published: February 2003

The ESR line shape and width of a trapped electron (et−) has been measured in 34% 17O enriched 10M NaOH alkaline ice glass at 77 K. The second moment of et− due to 17O coupling is 134 G2. Analysis of the second moment contributions from 17O coupling together with the constraint from electron spin echo studies that the et−–O distance is greater than 2 Å show that the et−–17O hyperfine coupling is mainly isotropic. Simulation of the et− ESR line under these constraints on 17O coupling and previous ones determined for H or D coupling for various numbers n of equivalent water molecules in the first solvation shell of et− give a best fit to the experimental line shape for n=6. For n?4 definite structure would be expected in the et− line shape which is not seen experimentally. The n=6 result together with previous data allows a rather complete geometrical description of the trapped, hydrated electron to be defined.
Interaction potentials for He–HF and Ar–HF using the Gordon–Kim method
Authors: Detrich John , Conn Robert W.
Published: February 2003

Interaction potentials computed by the method of Gordon and Kim are presented for the He–HF and Ar–HF systems. Results are given at five angles and five HF distances for 12 He–HF separations and 14 Ar–HF separations, spanning both the shallow attractive well and part of the repulsive core in each case. Agreement with variationally determined results for He–HF reported previously is very good and similar accuracy is expected for the Ar–HF results. These potentials should therefore be suitable for scattering calculations.