bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Formal Results in a Theory of Molecular Rearrangements: Photoisomerism
Authors: Gelbart William M. , Rice Stuart A.
Published: February 2004

Photoisomerism in the stilbene molecule is considered as a prototype of the general rearrangement reactions induced by absorption of light. The relevant experimental background is briefly reviewed, and the molecule is idealized in terms of a model describing a singlet vibronic level interacting (through the spin–orbit perturbation) with a nearly degenerate triplet state, which is in turn coupled (by vibronic interactions) to an isoenergetic set of closely spaced vibrational levels belonging to a lower triplet. A Green's function formalism is used to determine the time development of the system after it has been prepared in the initial state reached directly by optical excitation. The radiative and nonradiative processes are shown to proceed independently of one another in the statistical limit, and the over-all decay of the excited state is found to be exponential. The fluorescence quantum yield and radiative lifetime depend explicitly on the (solvent-specific) energy difference between the discrete singlet and triplet, and they are parameterized by the level density and coupling matrix elements of the zero-order states. Finally, our formal treatment is reconciled with simple kinetic descriptions, and it is suggested how this approach can be applied to still more general photochemical reactions.
Quenching of Cesium Resonance Radiation by Helium
Authors: Dodd J. N. , Enemark E. , Gallagher Alan
Published: February 2004

Using the phase-shift technique to measure excited-state lifetimes, upper limits of 1.5 × 10−14 cm3/sec and 3 × 10−14 cm3/sec have been established for the Cs(62P1/2re3/2) + He → Cs(62S1/2) + He quenching rate constants at 350° and 820°K. (In “cross-section” units these are equivalent to 10−19 cm2 upper limits.) The natural lifetimes were measured to be 30.8 ± 1.5 × 10−9 sec and 35.2 ± 1.5 × 10−9 sec for the Cs 62P3/2 and 62P1/2 states.
Metastable Peaks in the Mass Spectra of N2 and NO
Authors: Newton Amos S. , Sciamanna A. F.
Published: February 2004

Metastable ions dissociating by unimolecular transitions have been observed in the mass spectra of N2 and NO at (M / q)* = 7.00 and (M / q)* = 8.53, respectively. In N2 the transition of N2+ to N+ is shown to occur from a state with an A.P. of 24.9 ± 0.3 eV. The kinetic-energy release is 0.55 ± 0.10 eV; hence the dissociation is to the limit N+(3P) + N(4S0) at 24.30 eV. In NO the dissociation is to the limit O+(4S0) + N(4S0) at 20.101 eV. The observed A.P. and kinetic-energy release are 20.2 ± 0.2 and 0.04 ± 0.02 eV, respectively. Possible mechanisms of metastable dissociation by tunneling or predissociation are suggested.
Vibronic Interactions between nπ* and ππ* States of Polycyclic Azines and Aromatic Aldehydes: A Study of Perturbing Vibrations from Phosphorescence Spectra
Authors: Lim E. C. , Li R. , Li Y. H.
Published: February 2004

It has been shown that out-of-plane hydrogen wagging vibrations of CH groups, adjacent to the heteroatoms, are responsible for the appearance of relatively strong, in-plane polarized bands in π*→π phosphorescence of p-methoxybenzaldehyde and dibenzo[f, h]quinoxaline. In dibenzo[f, h]quinoxaline, these hydrogen vibrations are more effective than the out-of-plane ring vibrations in inducing the in-plane polarized phosphorescence intensity through vibronic spin–orbit coupling. In dibenzo[a, c]phenazine, where there is no CH group adjacent to the nitrogen atoms, the vibrational modes which give rise to the more intense in-plane polarized bands are out-of-plane ring modes. These results indicate that the nπ* state(s) is involved as an intermediate state(s) in vibronic spin–orbit coupling.
Slow Neutron Inelastic Scattering Study of Light Water and Ice
Authors: Harling O. K.
Published: February 2004

The results of an extensive slow neutron inelastic scattering study of H2O at 268° and 299°K are reported. A high-energy resolution spectrometer was used to obtain the double differential scattering cross sections over a wide range of energy and momentum transfers. Energy transfers to 0.6 eV and momentum wavevector transfers (k = ΔP / ℏ) to 32 Å−1 were measured for the liquid and solid phases of H2O. The differential cross sections exhibit considerable structure corresponding to hindered rotational motions of the H2O molecule as well as the intramolecular bending and stretching modes of vibration. In the case of ice the angular dependence of the scattering under the hindered rotation band is in good first-order agreement with the distribution calculated for a proton assumed to be bound in an isotropic elastic force field. The scattering properties of water and ice are presented in terms of the scattering law. In the latter form the results are compared to the calculated scattering using the McMurry–Russell modification of the Nelkin model, and the Egelstaff–Schofield theory for an incoherent scatterer with a Gaussian self-correlation function. Spectral densities for the modes of H2O, in water and ice, have been obtained and used with program leap to regenerate scattering functions, which are in good agreement with the experimental results. The rms amplitude of the proton motions has been obtained from the spectral density.
High-Temperature Phase Transition in RbH2PO4
Authors: Blinc R. , O'Reilly D. E. , Peterson E. M. , Williams Jack M.
Published: February 2004

The high-temperature phase change in tetragonal RbH2PO4 at 86°C is found to result in a quasi-irreversible transition to a monoclinic modification which seems to be isomorphous with monoclinic RbD2PO4 and KD2PO4. The transition is accompanied by a distortion of the PO4 groups and an ordering of the protons. From the analogy with monoclinic KD2PO4 it seems probable that the protons attach to one upper and one lower corner of a PO4 group giving rise to pyroelectric behavior along the b axis. The similarity of the infrared spectra of the high-temperature forms of RbH2PO4 and KH2PO4 demonstrates that the above statements are valid for KH2PO4 as well.
Isotropic Hyperfine Splittings and Molecular Structure in the PF4 Radical
Authors: Higuchi Jiro
Published: February 2004

The PF4 radical, as an example of a radical containing both fluorine and second-row atoms, is treated using simple quantum-chemical methods. It is possible to estimate the structure from only the isotropic hyperfine splittings. In the present work, the molecular structure of the PF4 radical is assumed to belong the symmetry C2υ with all the P–F internuclear distances equal to 1.57 Å. The calculations are performed by using the self-consistent field atomic orbitals. The bond angles are obtained from both the electron pair bond and the extended Hückel molecular orbital treatment by comparing the calculated hyperfine splittings with the observed values and are in fair agreement with each other. The most probable values are ∠F1PF1 = 174° ± 5° and ∠F2PF2′ = 109° ± 9°, which are fairly close to those of the SF4 molecule. The isotropic hyperfine coupling constant of the two fluorine nuclei making the larger bond angle, ∠F1PF1′, is larger than that of the other pair making the smaller angle, ∠F2PF2′.
Nonlocal Hydrodynamic Equations and the Spectrum of Critical Opalescence
Authors: Mistura L. , Sette D.
Published: February 2004

Both the thermodynamic theory of fluctuations and the linearized hydrodynamics equations are modified in order to take into account nonlocal effects. The description is based on the assumption that the entropy of the system is a functional of the energy and number density which can be expanded in a functional Taylor series about the homogeneous equilibrium state. In this way the well-known difficulties which arise with the “local functional expansion” of the semithermodynamic method are avoided. The modifications to be expected in the Landau–Placzek theory for the spectrum of critical opalescence are investigated. In particular, the angle or k dependence of the sound velocity, the Landau–Placzek ratio, and the width of the central component are discussed.
Coexistence Curve for 3-Methylpentane–Nitroethane near the Critical Point
Authors: Wims Andrew M. , McIntyre Donald , Hynne Finn
Published: February 2004

The coexistence curve for the liquid mixture 3-methylpentane–nitroethane has been obtained using a visual and a float technique. A detailed analysis of the data shows that the composition differences of the coexisting liquid phases are proportional to (tc — rpar;β, where β = 0.340 with a standard deviation of 0.010. As a result of this analysis and an analysis of the earlier work of Rice and Zimm it is shown that the value of β for binary liquids is not significantly different from the value for gas–liquid systems.
Analysis of the Pure Rotational Absorption Spectra of Hydrogen Sulfide and Deuterium Sulfide
Authors: Miller R. E. , Leroi G. E. , Hard T. M.
Published: February 2004

The far-infrared spectra of H2S, D2S, and H2S−D2S mixtures at low pressures have been obtained under high resolution. The analysis of H2S in the pure rotation region has shown that the rotational and distortion parameters established from the vibration–rotation measurements by Edwards are appropriate to account for the observed spectrum. For D2S, comparison of the observed and theoretical spectra suggests that the previously established parameters should be modified slightly. New values for the rotational and distortion parameters for D2S have been derived from far-infrared and microwave information by the combination–difference method. They are as follows: A0 = 5.4918, B0 = 4.5113, C0 = 2.4445 , τzzzz = − 0.00213, τxxxx = − 0.00117, τxxzz = 0.00113, τxxxz = − 0.00036 cm−1.
Thermal and Magnetic Study of Bonding in CsCuCl3
Authors: Rioux F. J. , Gerstein B. C.
Published: February 2004

The heat capacity and magnetic susceptibility of CsCuCl3 powder have been measured in the ranges 5°–300° and 2°–230°K, respectively. The susceptibility deviates from Curie–Weiss behavior below 55°K and the heat capacity exhibits a sharp peak, characteristic of cooperative behavior, in the neighborhood of 10.4°K. The behavior of this system is interpreted using a molecular orbital picture in which square planar coordinated copper atoms interact via a linear antiferromagnetic exchange above 10.4°K and order three dimensionally below this temperature. The following values are found for the thermodynamic functions: S°298.15 = 213.401 J (gfw·deg)−1), − (G°298.15 − H0°) / T = 120.544 J (gfw·deg)−1. A least-squares analysis of χMvs 1 / (T + θ) for all data above 77°K was performed. It was found that C = 0.458 ± 0.003, emu·deg/mole, (χD + χTIP = − 0.000058 ± 0.00003, emu/mole and θ = − 3.50°K. The quoted limits of accuracy are the standard deviations.
Simultaneous and Induced Electronic Transitions in Oxygen. I
Authors: Krishna V. G.
Published: February 2004

A fairly general theory of the relative intensities of the transitions Δ1gΔ1g←Σ3gΣ−3g− and Σ2gΔ−1g←Σ2gΣ−2g− in oxygen is given. The theory rests on the posulate that the terms in the above transitions mix with other bimolecular terms due to the intermolecular forces. Intermolecular exchange is shown to be essential for a successful interpretation of these transitions. Calculations are done neglecting the intermolecular overlap, but including all the electrons in the theory. All the allowed interactions, in the absence of intermolecular overlap, are considered in the theory. No assumption regarding the geometry of the O2···O2 pair is made. The theory predicts that relative oscillator strengths of the above two transitions (former to latter) should be 1.20. This is in excellent agreement with the experimental results. Theoretical predictions are shown to be unaffected when the intermoledular overlap is included in the calculations. The above results are derived from the ratios of interactions and thus are independent of approximations commonly used in the evaluation of integrals.
Competitive Unimolecular Decomposition in Chemically Activated Radical Systems. Isopropyl Radical Rupture
Authors: Larson C. W. , Rabinovitch B. S.
Published: February 2004

The competitive unimolecular decomposition of vibrationally excited 5-methyl-hexyl-3· (5MH3·*) and 3,4-dimethyl-pentyl-2· (34DMP2·*) radicals was studied in chemical activation systems in which H atoms were added to suitable olefins. The relative rate of isopropyl versus methyl-radical rupture from each radical yields D0°(iPr–H) = 92.8 kcal mole−1. Absolute rates of decomposition of 5MH3·*, 2MH3·*, and 34DMP2·* are compared to values obtained from the theoretical model and show good agreement The reactions of isopropyl radicals with 5MH3·, 2MH3·, and 34DMP2· radicals are discussed briefly; disproportionation-recombination ratios are obtained and compare favorably with values calculated according to an empirical prescription given previously. The measurement of the relative rates of decomposition of 5MH3·* and of 2MH3·* in the pseudocompetitive reaction system, H+trans-2-methylhexene-3, provides a relation between the energetics of the 5MH3· radical and the 2MH3· radical and supports D0°(5MH3·–H) = D0°(2MH3·–H). A summary of bond dissociation energies determined by the present method is given.
Experiments on Er3+ in SrF2. II. Concentration Dependence of Site Symmetry
Authors: Brown M. R. , Roots K. G. , Williams J. M. , Shand W. A. , Groter C. , Kay H. F.
Published: February 2004

Electron spin resonance has been used to follow the changes of site symmetry that occur in rare-earth-doped SrF2. The main conclusions that may be drawn are that the variation of site from tetragonal to trigonal as one goes through the rare-earth series Ce3+ to Er3+ can be explained by a calculation of the relative energies of interstitial fluorine ions and that the concentration dependence of the trigonal and cubic sites of Er3+-doped SrF2 can be explained by the sweeping action of dislocations for both the charge compensating and erbium ions.
Bare-Nucleus and Screened-Nucleus Perturbation Theory for He2
Authors: Goodisman Jerry
Published: February 2004

In the bare-nucleus perturbation theory, where the full interelectronic repulsion is taken as the perturbing part of the Hamiltonian, determination of the first-order wavefunction for a closed-shell system reduces to a set of two-electron problems. Only in the evaluation of the energy do three-electron integrals appear. One can thus produce a correlated wavefunction (containing interelectronic distances explicitly) without evaluation of three-electron integrals as arise in the variational method. After a review of the necessary formulas, we present calculations for He2. The convergence of the energy series is disappointing. However, the same formalism can be used when any one-electron local operator is taken as zero-order Hamiltonian. In particular we present screened-nucleus calculations, the zero-order Hamiltonian corresponding to noninteracting electrons moving in the field of nuclei of charge 1.5. Here, our energy through second order is as good as the best variational calculations.
Electronic Structure of Luminescence Centers of ZnS Phosphors Activated with Impurity Ions of s2 Configuration (I) ZnS:Bi Phosphors
Authors: Uehara Yasuo
Published: February 2004

The excitation, reflection, and fluorescence spectra and glow curves of various ZnS:Bi phosphors were measured accurately. A, B, and C bands with peaks at 6200, 4350, and 4060 Å (room-temperature values), respectively, were found in the visible region of excitation or reflection spectra. These bands were analyzed by using Sugano's molecular orbital theory. The position of A, B, and C bands and the calculated ratio of the diple strength of C band to that of A band are consistent with each other. Thus, it is possible to conclude unambiguously that the resonance transitions between the ground (A1(1S0) and excited states (T2(1P1), T1(3P2), and T2(3P1)) of the localized Bi3+ center produce the A, B, and C bands or the observed red (7600 Å), orange (6200 Å), and green (5100 Å) emission bands. Furthermore, the excitation lines or bands in the uv region of spectrum were analyzed. The interpretation for the glow characteristics was also given.
Projected Hartree Product Wavefunctions. III. Comparison with the CI Method for H2
Authors: Morrison R. C. , Gallup G. A.
Published: February 2004

Calculations of the energy of H2 have been performed using both the projected Hartree–Fock (PHF) method and a full CI method in the same basis for comparison of the two methods. It is discovered that PHF can account for 86% of the correlation energy, whereas CI will account for 88% of the correlation energy.
Cadmium-Photosensitized Interconversion of cis-, trans-, and geminal-Ethylene-d2
Authors: Hunziker Heinrich E.
Published: February 2004

Quantum yields of the reactions following quenching of Cd(53P1) atoms by cis-, trans-, and geminal-ethylene-d2 have been determined at 325°C and ethylene pressures of 3 and 13.5 torr. Cis–trans isomerization and intramolecular hydrogen scrambling, the latter decreasing with pressure, were observed. The sum of the quantum yields of the two processes is unity. Acetylene was formed with quantum yields of (5.6 ± 0.5) × 10−3 at 3 torr and (1.5 ± 0.1) × 10−3 at 13.5 torr. Isomerization and decomposition reactions are interpreted as consequences of the formation of triplet ethylene molecules in the quenching process. A modified mechanism for these reactions initiated by mercury, cadmium, and organic photosensitizers is proposed.
Gaussian-Type Functions for Polyatomic Systems. II
Authors: Huzinaga Sigeru , Sakai Yoshiko
Published: February 2004

The use of a linear combination of Gaussian-type orbitals (CGTO), instead of an individual Gaussian-type orbital (GTO), as a unit of basis functions for large-scale molecular calculations, is discussed. A systematic construction of the CGTO basis functions is attempted and the results for the atoms from Li through Ar are reported.
NMR Study of Molecular Configuration and Order in a Fluorinated-Liquid–Crystalline Schiff Base
Authors: Bravo N. , Doane J. W. , Arora S. L. , Fergason J. L.
Published: February 2004

The fluorine and proton spin resonances in the nematic–liquid–crystal state of terephthalbis (amino-fluorobenzene) are studied using the method of moments. The second moment of the proton line has a large dependence on the molecular configuration as well as on the degree of molecular order. The fluorine second moment, on the other hand, has a negligible dependence on the configuration and is used to obtain a measure of the order. With the degree of order known, the second moment of the proton resonance is used to examine possible configurations the molecule may follow. The results rule out the possibility of a planar molecule as well as a molecule in which the aromatic rings and the –N=CH– linkage groups are allowed to rotate around their bonds in an unhindered fashion. Best agreement with the data is found for the case where the plane containing the linkage group makes a preferred angle near 20° relative to the plane of the terminal aromatic rings. The temperature dependence of the proton spectrum is also interpreted in terms of the molecular order.
Infrared and Raman Spectra of Substituted Hydrazines. I. Methylhydrazine
Authors: Durig J. R. , Harris W. C. , Wertz D. W.
Published: February 2004

The infrared gas phase spectra of methylhydrazine (NH2NHCH3), methylhydrazine-d3 (ND2NDCH3), and methylhydrazine-d6(ND2NDCD3), have been measured from 33 to 4000 cm−1. The infrared and Raman spectra of the corresponding compounds in the liquid state have also been recorded. A complete vibrational analysis based on band intensity, position, and isotopic shift is presented. A series of sharp Q branches in the far-infrared region facilitated calculations of the torsional barriers. By assuming that a symmetrical threefold cosine potential governs both rotors in NH2NHCH3 we calculate barriers of 3.67 and 3.72 kcal/mole for the methyl and amino torsions, respectively. The intensity of the 3182-cm−1 line of NH2NHCH3 has been studied as a function of temperature. The ΔH° for H-bond formation is found to be − 418 cal/mole. Thermodynamic functions for NH2NHCH3 have been calculated for the temperature range 200°–3000°K on the basis of a rigid rotator, harmonic oscillator model.
Quantum Transition Probabilities for Atom–Triatomic-Molecule Collisions
Authors: Grimaldi John J. , Endres Paul F. , Wilson David J.
Published: February 2004

The method of Shuler and Zwanzig is extended to permit the calculation of collisional transition probabilities for triatomic molecules having harmonic intramolecular potentials and interacting impulsively with the bombarding atoms. Only colinear systems are considered. The results are qualitatively similar to those obtained for atom–diatomic systems. Excitation of the symmetric mode of oscillation is favored over the antisymmetric mode in the systems considered.
Floating Spherical Gaussian Orbital Model of Molecular Structure. VI. Double-Gaussian Modification
Authors: Rouse Robert A. , Frost Arthur A.
Published: February 2004

The floating spherical gaussian orbital model is modified to improve molecular energies and geometry by using a linear combination of two concentric spherical Gaussian orbitals (a double Gaussian) as the localized orbital. The double-Gaussian model was applied to hydrogen, the first-row atom hydrides, and a series of hydrocarbons. Bond lengths are predicted within 5.8% and bond angles within 6.6% for all the cases investigated. Molecular energies are generally 96% of Hartree–Fock values, and bond angles are improved.
Molecular g Values, Magnetic Susceptibility Anisotropies, and Molecular Quadrupole Moments in Ketene
Authors: Hüttner W. , Foster P. D. , Flygare W. H.
Published: February 2004

The high-field molecular Zeeman effect for ketene has been observed yielding accurate molecular g values and the magnetic susceptibility anisotropies. The results are gaa = − (0.4182±0.0009), gbb = − (0.356 ± 0.0013), gcc = − (0.0238 ± 0.0006), 2χaa–χbb–χcc = − (5.04 ± 0.65) × 10−6erg / G2·mole, and 2χbb–χaa–χcc = –(0.19 ± 0.55) × 10−6erg / G2·mole. The a axis is along the CCO bond, and the c axis is perpendicular to the molecular plane. A combination of arguments shows that the molecular g values are all negative, leading to the molecular quadrupole moments of Qaa = − (0. ± 0.3) × 10−26esu·cm2, Qbb = + (3.8 ± 0.4) × 10−26esu·cm2, and Qcc = − (3.1 ± 0.4) × 10−26esu·cm2. The paramagnetic susceptibility tensor elements are χaap = (10.9 ± 0.1) × 10−6, χbb = (125.3 ± 0.5) × 10−6, and χccp = (130.8 ± 0.4) × 10−6, all in units of erg/G2·mole. The ground-state electronic density is discussed and compared with formaldehyde. The differences in the average value of the squared electronic coordinates are 〈b2〉 − 〈c2〉 = (0.8 ± 0.4) × 10−16cm2, 〈a2〉 − 〈b2〉 = (26.6 ± 0.4) × 10−16cm2, and 〈a2〉 − 〈c2〉 = (27.4 ± 0.4) × 10−16cm2.
Xenon-Photosensitized Decomposition of Methane at 1470 Å
Authors: Sieck L. Wayne
Published: February 2004

The xenon-sensitized decomposition of methane and methane–ethylene mixtures has been investigated in the vapor phase at 1470 Å. Quantum yield determinations and analyses of the isotopic composition of the hydrogens and ethanes obtained from CH4–CD4(1:1) mixtures under various conditions indicate that sensitization occurs by at least two concurrent mechanisms. The role of internal photolysis by resonating 1470-Å radiation was found to be negligible in all mixtures, and the existence of XeH as an important intermediate was inferred by chemical methods.
Generalized Oscillator Strength for 11S→21P Transition of Helium. Theory of Limiting Oscillator Strengths
Authors: Lassettre Edwin N. , Skerbele Ausma , Dillon Michael A.
Published: February 2004

Relative generalized oscillator strengths have been determined for the 11S→21P transition in helium as a function of momentum change of the colliding electron and normalized to the theoretical oscillator strength {calculated by Schiff and Pekeris [Phys. Rev. 134, A638 (1964) ]} at zero momentum change. The validity of the normalizing procedure is investigated theoretically and it is shown that the limit of the generalized oscillator strength at zero momentum change is equal to the optical oscillator strength for any atom or molecule at any incident energy regardless of whether the first Born approximation holds. The normalizing procedure is therefore justified. The results are compared with the experimental and theoretical oscillator strengths obtained by other investigators. The limiting relation for oscillator strengths is established under much more general conditions than in any previous research.
Studies in Configuration Interaction. III. General Analysis of the Two-Body Density Function
Authors: Cooper Ian L.
Published: February 2004

Rules are presented for the determination of two-body transition density functions for pairs of spin-coupled functions corresponding to the same spin quantum numbers. The results are expressible in a number of alternative forms, in particular with respect to a basis of “Heitler–London-like” geminals.
Charge-Overlap Effects. Dispersion and Induction Forces
Authors: Kreek H. , Meath William J.
Published: February 2004

For nondegenerate atom–atom and atom–ion interactions the long-range interaction energy is expressed as a sum of “nonexpanded” angular components. If charge overlap is neglected each of the nonexpanded energies goes to a well-defined limit; namely to one of the usual R−1-expanded induction or dispersion energies or else to zero (R is the internuclear separation). The R−1 expansions appear to be asymptotic expansions of the nonexpanded results and are valid only for large R. As specific examples the H–H+ and H–H interactions are considered as model systems for studying charge overlap effects in induction and dispersion forces. The calculations are carried out variationally using the complete discrete Laguerre functions of degree (2l + 2) as a radial basis set. The asymptotic nature of the R−1 expansions for these interactions is discussed by comparing the various expanded and nonexpanded results. The importance of the nonexpanded interaction energies is also discussed briefly in general.
Examination of the Adequacy of the 12–6 Potential for Liquid Argon by Means of Monte Carlo Calculations
Authors: McDonald I. R. , Singer K.
Published: February 2004

Monte Carlo calculations of thermodynamic properties of argon are reported for the temperature range between the triple point and the critical temperature at pressures up to 700 atm. It is shown that the Lennard-Jones 12–6 potential with the parameters proposed by Michels et al., viz., ε / k = 119.8°K and σ = 3.405 Å, leads to internal energies and pressures which are in fair agreement with the experimental values. The over-all agreement with experiment may be substantially improved by reducing the depth of the potential well to ε / k = 117.2°K. The use of other potentials, the importance of nonadditivity corrections, and the agreement between the Monte Carlo results and those obtained by the method of molecular dynamics are briefly discussed.
Rotational Properties Associated with the Heitler–London Model of H2
Authors: Beckel Charles L.
Published: February 2004

The first-order WBK approximation has been used to determine rotational constants Bυ and Dυ for the Heitler–London (HL) model of the H2 ground electronic state. Near-equilibrium characteristics of Bυ and Dυ are discussed briefly in terms of the potential expansion about re. Over-all, the HL and experimental Bυ curves have nearly the same shape. The HL Bυ curve has negative curvature at all υ converging at a slightly slower rate than the experimental curve at high υ. This slower convergence is associated with the 1 / r2 factor used in defining Bυ. The HL Dυ curve, like the corresponding experimental curve, rises rapidly in the vicinity of dissociation. Both increases are attributed to a breakdown in the approximation that treats the centrifugal reaction term as a perturbation of the rotationless problem. The reliability of the first-order WBK approximation is checked and found to lead to only slight errors in the Bυ and Dυ values.
Rice–Allnatt Theory of Transport for Rough Spheres
Authors: McCoy Benjamin J. , Dahler John S.
Published: February 2004

The Rice–Allnatt theory for liquids of monoatomic molecules is extended to rotating hard cores surrounded by symmetrical soft potentials. The kinetic equation is solved by the Chapman–Enskog method. Numerical values for the thermal conductivity, the shear viscosity, and the bulk viscosity coefficients are evaluated and tabulated to show the dependence on molecular moment of inertia.
Molecular Force Constants. I. Planar XY3 Molecules
Authors: Thirugnanasambandam P. , Srinivasan G. J.
Published: February 2004

An attempt has been made to evaluate afresh all the quadratic potential constants of planar XY3-type molecules and ions by Wilson's F − G matrix method using the spectral frequencies and certain simplifying considerations.
Two-Center Exchange Integrals between Slater-Type Atomic Orbitals
Authors: Mehler Ernest L. , Ruedenberg Klaus
Published: February 2004

A novel general formula is developed which expresses two-center charge distributions over Slater-type atomic orbitals as expansions over terms of the form (ξ − 1)k(ξ2 − 1)M/2ex(− αξ)Ylm(η,φ), where (ξ, η, φ) are elliptic coordinates. The formula is applied to derive compact expressions for the calculation of two-center exchange integrals arising from large basis sets. The program structure is discussed and computing times are quoted for these type integrals.
Dielectric Studies. XXIV. Considerations on the Cole–Cole Equations for Systems Undergoing Relaxation According to Budó's Equations
Authors: Magee M. D. , Walker S.
Published: February 2004

The accuracy of the determination of ε∞ from the Cole–Cole equations for systems which really relax by two Debye mechanisms is considered. The estimated value of ε∞ is shown to be too low but an empirical equation helps to formulate limits within which the true value is likely to lie. Errors incurred in ε∞ obtained by this method probably do not seriously influence relaxation time parameters obtained by a subsequent Budó analysis but approximations to ε∞ (such as nD2) which are likely to be low may give very misleading results. Relationships between the Cole–Cole distribution parameter (α) and mean relaxation time (τ0) and the Budó parameters (τ1, τ2, and C1) are presented and discussed.
Destruction of Metastable Helium Atoms in Binary Collisions
Authors: LoDato Vincent A. , Katsuura Kanji
Published: February 2004

A theoretical calculation of the total cross section of the destruction of metastable helium atoms He(23S) by ionization has been performed by means of the impact parameter method with a number of suitable approximations. The cross section obtained is of the order of 102 a02, which is in good agreement with the experimental order of magnitude of Phelps and Molnar, and shows the error in the theoretical calculation of von Roos.
Double Perturbation Theory for He-like Systems
Authors: Tuan Debbie Fu-tai
Published: February 2004

The He-like system is considered to be a spherical Harmonic oscillator with the electrons attracted to the nucleus by a Hooke's-law force, under two perturbations: (1) electronic repulsion, H(1,0), and (2) the difference between the harmonic oscillator potential and the actual nuclear Coulomb attraction, H(0,1). For the ground state, the first-order wavefunctions with respect to both perturbations are found in closed form. Exact expressions for both of the single perturbation energies through third order and the mixed perturbation energy ε(1,1) are derived. Calculations have been carried out on H−, He, Li+, and Be2+ for different choices of f, the Gaussian parameter of the zeroth-order harmonic oscillator wavefunction ψ(0,0). The choice f = (4 / 3π1/2) [Z − (1 / 2√2)] corresponding to the variational one-term Gaussian orbital of a He-like system gives the best total calculated energy, − 2.88210 a.u. for helium compared to the experimental and “exact” value of − 2.90372 a.u. From the study of the convergence of the perturbation energies, it is concluded that as far as correlation is concerned the first-order perturbation with respect to H(1,0) is accurate enough. Higher order perturbations with respect to the one-electron operator H(0,1) will be needed for highly accurate results. However, even at the first-order level the Gaussian character of ψ(0,0) is improved tremendously by the perturbation H(0,1). This is shown by the values of ε(0,2) + ε(0,3), of the order of − 0.4 to − 0.6 a.u.
Molecular g Values, Magnetic Susceptibility Anisotropies, and Molecular Quadrupole Moments in Ethylene Oxide
Authors: Sutter D. H. , Hüttner W. , Flygare W. H.
Published: February 2004

The first- and second-order molecular Zeeman effect has been recorded in ethylene oxide to yield the molecular g values and magnetic susceptibility anisotropies in the molecule. The magnetic susceptibility anisotropies are 2χaa − χbb − χcc = + (18.06 ± 0.58) × 10−6 and 2χbb − χaa − χcc = + (0.78 ± 0.97) × 10−6erg/G2·mole. The b axis bisects the COC angle and the a axis is also in the COC plane. Only the relative signs of the g values are experimentally determined. Arguments are presented which favor one of the two sets of signs giving gaa = − (0.0946 ± 0.0003), gbb = + (0.0189 ± 0.0004), and gcc = +(0.0318 ± 0.0006. The molecular quadrupole moments, with this choice of signs, are Qaa = + (2.5 ± 0.4) × 10−26, Qbb = − (4.3 ± 0.5) × 10−26, and Qcc = + (1.8 ± 0.8) × 10−26esu·cm2. The diagonal elements in the paramagnetic susceptibility tensor are χaap = (60.6 ± 0.3) × 10−6, χbbp = (67.3 ± 0.5) × 10−6, and χccp = (88.3 ± 0.5) × 10−6erg/G2·mole. The known value of the average magnetic susceptibility is combined with our values for the paramagnetic susceptibilities and anisotropies of the total susceptibility to yield the diagonal elements in the total and diamagnetic susceptibility tensors. The total susceptibilities are χaa = − (24.7 ± 0.7) × 10−6, χbb = − (30.4 ± 0.7) × 10−6, and χcc = − (37.0 ± 0.8) × 10−6erg/G2·mole and the diamagnetic susceptibilities are χaad = − (85.4 ± 0.9) × 10−6, χbbd = − (97.7 ± 1.1) × 10−6, and χccd = − (125.4 ± 2.0) × 10−6erg/G2·mole. The second moment of the ground-state electronic charge distribution is 〈a2〉 = (16.3 ± 0.4) × 10−16, 〈b2〉 = (13.3 ± 0.4) × 10−16, and 〈c2〉 = (6.8 ± 0.4) × 10−16cm2.
Radical Formation in X-Irradiated Glycine HCl
Authors: Box Harold C. , Budzinski Edwin E. , Freund Harold G.
Published: February 2004

Electron spin resonance spectroscopy was used to identify the electron and hole traps in single crystals of glycine HCl x irradiated at 4.2°K. Holes are trapped by the formation of Cl2− ions and electrons by the formation of O−/Cl−(NH3)+—CH2—C\OH Upon warming, the neutral radical CH2–COOH is formed, which is identical with the radical produced in irradiated crystals of the free amino acid. The advantage of using the hydrochloride salt in this investigation is that the Cl2− ions are very stable and it is possible to observe unequivocally that the neutral radical is formed concomitantly with the decay of the glycine HCl negative ion.
Approximate Higher Ionization Potentials for the Heavier Elements
Authors: Kastner S. O.
Published: February 2004

Approximate ionization potentials for the higher stages of ionization of elements Z = 31–92 are computed using the limiting screening constants of Froese. They are compared with available values for lower Z.
ESR Spectra of Oriented Polytetrafluoroethylene Subjected to 20-nsec Pulses of Electrons
Authors: Lerner N. R.
Published: February 2004

Samples of oriented polytetrafluoroethylene have been subjected to irradiation from a pulsed electron beam generator. The duration of the pulses was 20 nsec, and doses ranging from 0.8–14 Mrad were delivered to the samples. Working with oriented samples makes it possible to distinguish and identify two distinct species in the samples irradiated in air. The relative concentration of the two species varies as a function of the dose. In samples receiving larger doses of radiation the species –CF2–(CF–O–O)–CF2– dominates the ESR spectrum. At lower doses the species –CF2–O–O· makes a larger relative contribution to the ESR spectrum. Samples were also subjected to irradiation in vacuum. The ESR spectra obtained from the vacuum-irradiated samples before and after the admission of air is discussed. Samples were subjected (in air) to radiation from a 60Co source, ranging from 5–30 Mrad, at a dose rate of 0.43 Mrad/h. The species –CF2–O–O· dominates the ESR spectrum of 60Co irradiated samples. The details of the line shapes of the ESR spectra of samples irradiated in air are discussed.
Measurement and Correlation of Some Interaction Second Virial Coefficients from − 125° to 50°C. I
Authors: Brewer Jerome , Vaughn George W.
Published: February 2004

Interaction second virial coefficients have been measured from − 125° to 50°C in 25° increments for the following systems: N2–Ar, Ar–H2, Ar–He, Ne–Ar, N2–H2, N2–He, Ne–N2, H2–He, Ne–H2, and Ne–He. The excess second virial coefficients were reproduced usually within 0.1 cc/mole by measuring the pressure change of mixing two pure gases at constant temperature and volume. With these excess quantities and literature values of B11, the interaction second virial coefficients were calculated. The comparison between experimental interaction second virial coefficients and those calculated by the Kihara potential was considered good at the higher temperatures and fair to poor at the lower temperatures where the deviation was sometimes as much as 8 cc/mole. This deviation is probably mainly due to the assumption of the geometric-mean mixing rule for the characteristic energy between the dissimilar molecules. In the temperature range of − 125°–50°C, the excess quantity E was empirically correlated to the absolute temperature by the relation, E = αTβ where the value of β was essentially the same for most of the binary mixtures studied.
Beam Studies of the Energy Dependence of Hot-Hydrogen-Atom Reactions with Cyclohexane
Authors: Menzinger Michael , Wolfgang Richard
Published: February 2004

Beam studies of the energy dependence of hydrogen-atom-molecule reactions having appreciable thresholds are reported. Such investigations spanning the entire chemical range promise to be of importance in understanding the dynamics of reactive collisions. This work examines the interactions with solid cyclohexane of tritium ion beams, both T+ and T2+, having controlled energy between 1–200 eV. These ions undergo efficient charge transfer at the surface of the target to form hot tritium atoms of similar velocity. Labeled products are formed by hot-atom reactions, and their yields are measured by radio–gas chromatography. At high energies (≥ 30 eV), absolute yields for T+ beams are close to those found by the nuclear recoil technique. With T2+, high-energy yields are about 20% lower; this apparently corresponding to the fraction of ions forming unreactive T2 upon charge exchange. At lower energies, yields decline. The threshold for the T for H replacement is at 1.5 ± 0.5 eV. Hexenes and hexanes appear to result from processes in which a C–C as well as a C–H bond is ruptured. The threshold for such double displacement is at 4.5 ± 0.5 eV. Provided certain rather drastic assumptions are made, the energy dependence of the yields can be used to derive approximate excitation functions.
Temperature and Volume: The Independent Variables of State for Viscosity
Authors: Rudich S. W. , Lind John E.
Published: February 2004

The viscosity coefficients of molten tetrapropylammonium tetrafluoroborate and its phosphonium and arsonium analogs at 1 atm pressure show an anomalous relation to each other. When temperature and volume are used to define the state of the system, the relations between the viscosity coefficients become consonant with theory. Differences in molecular size and potential energy, so small that the viscosity is insensitive to them, can cause differences of several hundred atmospheres in the pressure of different fluids confined at the same volume and temperature. It is this sensitivity of the pressure to molecular parameters which exhibits itself in slight differences in molar volume at 1 atm pressure. These volume differences cause the “anomalous” behavior of the viscosity. A modified hard-sphere equation of a state with a Coulomb term based on a pseudolattice adequately describes the PVT isotherms at high pressure and predicts the thermal expansion coefficient and Coulomb energy.
Maximum Ionization Cross Section of Atoms
Authors: Tiwari Prabhakar , Rai D. K. , Rustgi M. L.
Published: February 2004

Various theoretical approaches for estimation of maximum ionization cross sections have been discussed and three new relations have been developed and used to evaluate maximum cross sections. Mann's calculations have been critically examined, and the present results have been compared with available experimental results.
Pulse Radiolysis of NO : Production of NO2 and N2O3 and the Production and Relaxation of Vibrationally Excited NO
Authors: Hochanadel C. J. , Ghormley J. A. , Ogren Paul J.
Published: February 2004

Radiolysis of NO with a 30-nsec pulse of 2-MV electrons produces absorption bands attributed to NO2, N2O3, and vibrationally excited NO. In pure NO at 1 atm, most of the NO2 forms during the pulse, but the formation of N2O3 is slower (τ = 0.3 μsec). The NO2 is produced by the reaction of O atoms with NO, and the pseudo-first-order rate constant for formation of NO2 in an 11% NO–Ar mixture is slightly lower than that calculated from published values. The N2O3 comes from the equilibrium NO2 + NO⇆N2O3, which is achieved in <1 μsec, orders of magnitude faster than the previously estimated lower limit. The sum of yields of the two products (10.6 ± 0.5 molecules/100 eV) was independent of the pulse dose, but the ratio G(NO2) / G(N2O3) increased with dose. This can be explained by a shift in the above equilibrium caused by the temperature increase produced by the pulse. Superimposed on the broad N2O3 band in the ultraviolet was a sharp band at 2362 Å, indicating population of the first vibrational level of NO. The relaxation lifetime was 5.8 μsec for 13% NO in Ar and 1.6 μsec for 41% NO, giving a quenching probability by NO of 2.1 ± 0.2 × 10−4 compared with 3.6 ± 0.4 × 10−4 reported by Basco, Callear, and Norrish. A small amount of absorption in the (0, 2) band at 2472 Å decayed with a lifetime ∼1.4 μsec, giving a probability for resonant vibration–vibration exchange of only ∼10−3.
Electron Spin Resonance of Gamma-Irradiated Single Crystal of Cytosine Monohydrate at 77°K
Authors: Herak J. N. , Galogaža V.
Published: February 2004

Single crystals of cytosine monohydrate have been irradiated and analyzed with electron spin resonance spectroscopy at 77°K. Two types of radicals have been observed and identified as the cytosine cation and anion radicals. The hyperfine splittings of the 14N and 1H nuclei for the cation radical are found to be in fairly good agreement with the predictions of the molecular orbital theory. The anion-radical hyperfine splittings could not be resolved in all crystal orientations. Both types of radicals rapidly disappear upon heating, probably via mutual recombination.
Dynamics of a Long Polymer Backbone
Authors: Bugl Paul , Fujita Shigeji
Published: February 2004

For the study of the dynamics of a polymer molecule in dilute solution a continuous wire model is proposed and investigated. This model is a refinement of the wormlike chain model introduced by Kratky and Porod such that the configurational energy depends not only on the curvature κ but also on the torsion τ, both of which may be considered as functions of the arc lengths measured from one end. The physical basis of considering such energy dependence is given from a general differential–geometrical viewpoint, and also by the explicit calculation of the elastic energy of an ideally thin wire, which is found to be ∫ 0lds18πR4[E(κ − κ0)2 + 2μ(τ − τ0)2], where E and μ are Young's modulus and the modulus of rigidity of the wire material; R is the radius of the circular cross section of the wire; κ0(s) and τ0(s) are the curvature and torsion of the space curve characterizing the wire of minimum energy. The dynamics of the model is formulated with the aid of Hamilton's principle of least action. In particular the wave propagation along the axis of a helical coil is investigated in detail. It is shown that the measurement of the propagation speed of a longitudinal wave along a polymer chain can lead to the quantitative estimate of the bending and twisting characteristics of the chain.
Neutralization of Isolated Ion Pair in Polar Media. II. Evolution of the Neutralization Process
Authors: Mozumder A.
Published: February 2004

In this paper we discuss the neutralization rate of an isolated ion pair in a polar medium as obtained from the prescribed diffusion solution of the Smoluchowski equation. Specifically, we consider the cases of water, methanol, and ammonia. A specific model with two diffusion constants and a time-dependent dielectric constant has been employed. The time dependence of the dielectric constant is taken, as in the previous paper, for the situation of fixed charge rather than for fixed external field. Numerical results have been obtained for the probability that the ion pair remains unneutralized at a given time and for the rate of change of this probability with time. A critical review is presented for the time–distance relationship.
Characterization of Ground-State Wavefunctions by Measured Electronic Properties. III. A Gaussian Basis Self-Consistent-Field Calculation for Nitrogen Trifluoride
Authors: Unland Mark L. , Letcher John H. , Van Wazer John R.
Published: February 2004

An LCAO MO SCF calculation has been carried out for nitrogen trifluoride using an uncontracted (73 / 73) Gaussian basis set. Energy parameters, dipole moment, field gradient, molecular quadrupole moment, second moments of charge, and population analysis are reported. The calculation is used to evaluate earlier wavefunctions obtained by more empirical methods. Combining experimental quadrupole-coupling-constant data with the calculated field gradient gives a nitrogen nuclear quadrupole moment of + 0.018 ± 0.003 × 10−24 cm2 which is in good agreement with earlier, less precise, estimates of this parameter.
Broad-Line NMR Study of H2O and D2O in Collagen Fibers
Authors: Dehl R. E. , Hoeve C. A. J.
Published: February 2004

The deuterium NMR spectra of D2O absorbed in parallel collagen fibers have been recorded for samples containing four different percentages of D2O. In all cases, the spectra consisted of a pair of lines, the separation of which is given by K(3 cos2θ − 1), where K is small compared to the rigid-lattice value and decreases with increasing moisture content of the fibers, and θ is the angle between the fiber axis and the magnetic field. The splitting is ascribed to quadrupole perturbation of the Zeeman levels of deuterium caused by slightly anisotropic but rapid reorientation of D2O molecules in the fiber lattice. Contrary to the interpretation by others, we have concluded from a comparison of the spectra of D2O and H2O in collagen: (1) that the center line in the H2O spectra is not due to water, and (2) that line broadening in the H2O spectra, both at high temperatures and in the presence of added salts, is due to proton exchange between the water molecules. Molecular motion causes both H2O and D2O splittings to be reduced to approximately the same fraction of their respective rigid-lattice splittings.