bluuebunny/crossref_metadata_2025 huggingface dataset:
Radio-Frequency Spectroscopy and Perturbation Analysis in CS A 1Π(υ = 0)
Authors: Field Robert W. , Bergeman Thomas H.
Published: February 2004

Electric dipole rf resonances are observed in levels J = 1 through 9 of A 1Π(υ = 0) of CS. A CS molecular discharge lamp is the source of the pumping ultraviolet radiation. Lambda doubling intervals ranging from 13 to 1787 MHz (100 kHz accuracy) and effective dipole moments of 0.6699 to 0.6786 D (0.0005 D relative error) for 3 ≤ J ≤ 9 are obtained. These data are combined with measurements from the optical spectrum to extend the analysis of perturbations affecting A 1Π(0). Parameters for the off-diagonal spin–orbit interaction between this and several triplet states, perturbation corrections to the empirical term value T0 and rotational constant B0, and intermixing coefficients for the Stark effect are obtained. The observed variation of the Stark effect with rotational level is analyzed to give two dipole moments: A 1Π(υ = 0), μ = 0.63(4) D; a′ 3Σ+(υ = 10), μ = 1.7(4) D. Error limits include probable effects from neglected minor components. The factors contributing to state selectively in optical pumping of excited electronic states by the molecular discharge lamp or by white light are discussed.
Experimental Test of the Reaction O(1D)t+CO2→CO+O2
Authors: Felder W. , Morrow W. , Young R. A.
Published: February 2004

The rate of evolution of CO from the 1470-Å photolysis of CO2–O2 mixtures was compared with the rate of evolution of CO from the 1470-Å photolysis of pure CO2 using the fluorescence of the CO4+ to follow CO. It had been suggested that the translationally “hot” O(1D) formed in the mixture (from the 1470-Å photolysis of O2) could react with CO2 to yield CO+O2 (or O+O). It was concluded from these comparisons that the “hot” O(1D) apparently does not ultimately yield CO by reaction with CO2.
Approximate Single-Center Perturbation Calculations. I. Ground States of H2+, HeH2+, H2, HeH+, He22+, and Linear Symmetric H3+
Authors: Mackrodt W. C.
Published: February 2004

Using the “molecular puff” equations as a starting point, first-order perturbation equations are solved for H2, HeH+, He22, and linear symmetric H3+, and first- and second-order equations for H2+ and HeH2+. The perturbation wavefunctions are expanded in partial waves and the resulting equations solved by numerical integration for the 1sσ ground states. The errors in the calculated energies are in the range 0.5–10.0 kcal/mol and represent a considerable improvement on similar calculations reported by Hauck, Kim, Parr, and Hameka [J. Chem. Phys. 47, 2677 (1967)].
Calculation of the Hyperfine Splittings of CH. Cusp Constraint of a Wavefunction
Authors: Poling S. M. , Davidson E. R. , Vincow G.
Published: February 2004

It is shown that applying an electron–nuclear cusp constraint to a CI wavefunction is equivalent to omitting from the basis set a particular linear combination of atomic orbitals. This result is exploited in constructing cusp-constrained wavefunctions for CH. Several small STO basis sets, a double-zeta basis, Cade and Huo's basis, and a subset of their basis were used to calculate hyperfine couplings for CH. The last two sets were also used with cusp constraints. Reasonable results are obtained for the proton splitting using either the free atom 1sH orbital or the 1sH orbitals from Cade and Huo's basis. Any attempt to use optimum orbital exponents with a small basis gave unreasonable results. The cusp constraint produced little change in the results for the largest basis. Our best theoretical estimate for aH is − 18 ± 3 G. Carbon-13 splittings are much more sensitive to the basis set. Even for the largest basis the results were still strongly affected by the cusp constraint. Our best estimate for aC is + 10 ± 15 G.
Composition Dependence of the Thermal Diffusion Factor for the H2–He System
Authors: Taylor W. L. , Weissman Stanley
Published: February 2004

Ghosh et al. and Mathur and Watson have reported maxima and minima in the curves obtained when the thermal diffusion factor, αT, of H2–4He mixtures is measured as a function of composition. These workers have interpreted their results as due to inelastic collisions in the thermal diffusion process but as yet no theoretical treatment has predicted these anomalies. Previous experimental data have also given no such indication. We have measured αT in a 20-tube trennschaukel at 215, 273, and 373°K at approximately 5% composition increments and find no evidence of the aforementioned behavior. We have fitted 1 / αT, which theory predicts to be a linear function of composition, to a straight line function by the method of least squares and obtained an average deviation of ∼ 2%–3% in all cases which is less than the estimated experimental uncertainty. The data of Mathur and Watson were analyzed in the same fashion with similar results for all but the lowest temperature. We have concluded that the data of Ghosh et al. are in error and, furthermore, that while we agree essentially with the experimental results obtained by Mathur and Watson between 200 and 375°K, we cannot accept their interpretation of the data. Theoretical calculations were performed for the third Chapman–Enskog approximation to the thermal diffusion factor, [αT]3, using both the (12–6) and (exp-6) potentials. The values obtained using the (exp-6) potential with the Mason–Rice parameters agreed excellently with our experimental results.
Rotational Spin–Lattice and Spin–Spin Quadrupole Relaxation in Perdeuterated Glycerol
Authors: Drake P. W. , Meister R.
Published: February 2004

The deuteron spin–lattice and spin–spin relaxation times have been measured in glycerol-d8 at the resonance frequency of 5 MHz and over the temperature range from − 25 to + 70°C using “spin–echo” techniques. The spin–lattice relaxation times exhibit a minimum at − 13°C and this minimum value is employed in directly determining the value of the deuteron quadrupole coupling constant (DQCC) in glycerol. Values of the DQCC obtained lie between 139 and 158 kHz. These values of the DQCC and the measured relaxation times were employed to determine the average correlation times (τ̄Q) for the molecular motions responsible for the quadrupolar relaxation. These correlation times are associated with the rotational reorientation of the molecules. A comparison of τ̄Q with the average dielectric relaxation times indicates that the rotational reorientation of glycerol is best described as large-angle jump diffusion.
Crystal Reflection Spectrum of Dibenzoselenophene
Authors: Gerhold George A. , Clark L. B.
Published: February 2004

Dibenzoselenophene forms orthorhombic crystals based on a dimeric unit. The geometry of the dimer pair makes this crystal an ideal case for the appearance of charge-transfer bands. All bands below 50 kK can be assigned to single-molecule transitions; no charge-transfer bands appear. The polarization directions for the transitions are assigned.
Thermal Diffusion Columns and Intermolecular Potential. II The Noble Gases Ne, Ar, Kr, and Xe
Authors: Hidalgo M. A. , Yarza J. C. , Alvarez D. González , Savirón J. M.
Published: February 2004

One glass concentric-tube- and two hot-wire-type thermal diffusion columns are used to study column operation for inert gases. It seems that the relation, pexptl* = p̄ptheoret*, holds for all inert gases, in the concentric-tube-type column, p̄ being a geometric constant independent of temperatures and gases. The aforesaid relation, as well as ln Q̄0 exptl* = m̄ ln Q̄0 theoret*, are extended to krypton in hot-wire-type columns. An excellent proportionality between FJO theory and experiment is found. On this basis, a study of the influence of ε / k on the relation for the separation factor is carried out. Application is made to gas krypton, using the Lennard-Jones (12–6) potential model.
Photoionization of Europium and Thulium: Threshold to 1350 Å
Authors: Parr Albert C.
Published: February 2004

Photoionization spectra of europium and thulium are reported from threshold to 1350 Å. The ionization efficiency in this region is found to be dominated by autoionization. Autoionization structure, believed to be due to 4fN6s2 → 4fN5dnp transitions, is interpreted and other strong resonances listed. The ionization potential of europium is determined to be 5.664 ± 0.008 eV and that of thulium to be 6.180 + 0.008 eV.
One and Two Photon Electron Ejection from TMPD in Fluids Supporting Large Electron Mobilities
Authors: Takeda S. S. , Houser Nathan E. , Jarnagin R. C.
Published: February 2004

The photoejection of electrons from tetramethylparaphenylenediamine in fluid solution has been examined by pulsed and steady light excitation. In addition to the previously documented tandem two quantum ejection of a quasifree electron in fluids, a one quantum ejection has been found and a kinetic interpretation given. The quasifree electron was observed through transient photocurrent measurement and the electron mobility in several silane and hydrocarbon fluids was estimated. The values found range from 93 cm2 V−1·sec−1 to 2 × 10−2 cm2 V−1·sec−1 in tetramethylsilane to hexane, respectively, and appear to be limited by features of solvent molecular structure. A continuum state of TMPD appears to lie at about 4.5 eV and higher. This state is accessible by a monophotonic process from the ground state of TMPD and by a biphotonic process via the triplet state of TMPD.
Classical Trajectory Calculations of the Scattering of TlF on Ar in Thermal Beams
Authors: van de Ree J.
Published: February 2004

With the method of classical mechanics a statistical number of trajectories is calculated for thermal collisions of TlF on Ar. Two potential models developed in a previous paper have been used. Because of the absence of out-of-plane scattering the calculations are restricted to two-dimensional collisions. Total and differential cross sections are evaluated for initial rotational states j = 1 and j = 30 in the range of relative velocities between 150 m/sec and 800 m/sec. Because of the high frequency of inelastic collisions and the important part played by orbiting collisions measurements of the cross sections are incompatible with the determination of potential parameters in the manner customary for atomic scattering. The effects of the various dynamical processes which dominate in the collisions can be followed in differential measurements. Two types of orbiting can be distinguished, one with weak and one with strong coupling between rotational and orbital angular momenta. In both types the attraction by permanent induction forces prevails, because the asymmetric potential favors an approach of argon from the fluorine side of the molecule.
Group Theoretical Analysis of Vibronic Interactions in Molecules
Authors: Alper Joseph S.
Published: February 2004

The canonical transformation methods previously developed for the solution of problems involving dynamical vibronic interactions in molecules are examined by means of group theory. It is found that SU2 and the quantum mechanical group (the group generated by the position and momentum operators) afford physical insight into the reasons for the success of the transformation methods. In each method, the Hamiltonian is closely related to and can be written in terms of the elements of the groups. In these methods we use the fact that the basis functions of the representations of the quantum mechanical group are the harmonic oscillator functions, the natural functions for the problem. Products of representation matrices are in fact the matrix elements of the Hamiltonian. We also make use of the fact that the representation matrices are themselves the wavefunctions of the two-dimensional isotropic harmonic oscillator. In addition to the physical insight, the group theoretic methods simplify the calculations.
Exciton Self-Trapping in Rare-Gas Crystals
Authors: Martin Marlo
Published: February 2004

The problem of exciton self-trapping in rare-gas solids is investigated from a dynamical point of view. Experimental ultraviolet emission spectra from rare-gas solids and liquids have been interpreted as arising from the radiative decay of an excited-state dimer which becomes localized in the substance. This embedded dimer can arise from electron capture by a self-trapped hole (R2+), or by the dynamical trapping of an exciton into an excimer state (R2*). A study of the vibrational relaxation of a molecule embedded in a solid leads to a fast trapping process in which an exciton becomes localized for all the heavy rare-gas substances. This localization is achieved within 6 × 10−12 sec by means of a resonant transfer relaxation process in which two neighboring atoms lose sufficient energy (∼ 0.5 eV) to become stabilized in a lower vibrational state of the excimer.
Energy Distribution in Field Emission from Krypton Covered Tungsten
Authors: Lea Colin , Gomer R.
Published: February 2004

Work functions and energy distributions as functions of relative coverage have been obtained for Kr adsorbed on the (110), (100), (111), and (112) planes of a tungsten field emitter, from zero coverage to several monolayers. Work function results agree with previous measurements where overlap exists. The data could be fitted by the Topping equation for depolarization, yielding polarizabilities in reasonable agreement with the atomic value if HCP monolayer densities were used, on all but the (110) plane where a higher value resulted. Energy distribution in the submonolayer range show no deviations from free-electron-like behavior, except possibly on the (110) plane where a strong antiresonance seems to occur. On the (100) surface the Swanson anomaly found in the distribution from the clean surface decreases monotonically with Kr coverage, indicating that it is probably due to surface states. Work function values in the multilayer range can be interpreted to mean that the conduction band of Kr lies ∼ 1.4 eV below the vacuum. Energy distributions for multilayers deviate from free-electron-like behavior; both electric and inelastic scattering processes could explain this result.
Quenching of Naphthalene Luminescence by Oxygen and Nitric Oxide
Authors: Jones Peter F. , Siegel Seymour
Published: February 2004

The quenching of naphthalene-h8 and naphthalene-d8 luminescence by O2 and NO in the absence of molecular diffusion is investigated. By measurement of the dependence of fluorescence and phosphorescence yields and lifetimes on quencher concentration, it is possible to separate the effects of singlet and triplet electronic state quenching and to determine the critical quenching radii R0. No static quenching of naphthalene fluorescence is observed for O2 concentrations of up to 0.25M. Thus, the corresponding R0 value in the Perrin formula is less than or equal to 7.1 Å. Conversely, the concentration dependence of naphthalene-h8 and naphthalene-d8 triplet state quenching by O2 is in excellent agreement with the Perrin formula, and the corresponding R0 values are 9.9 ± 0.3 and 9.8 ± 0.3 Å, respectively. Contrary to the Perrin model, but in agreement with the theory for quenching by an exchange interaction, the quenching process is competitive with the normal decay rate, and the phosphorescence decay curves become nonexponential with increasing O2 concentration. The rate constant for naphthalene triplet-state quenching by O2 decreases upon the deuteration of naphthalene. This suggests that enhanced intersystem crossing, and not energy transfer, is the dominant triplet-state quenching mechanism, at least for naphthalene-O2 separations ≈ 10 Å. The concentration dependence of naphthalene-h8 and naphthalene-d8 fluorescence quenching by NO is in excellent agreement with the Perrin formula, and the corresponding R0 values are 12.3 ± 0.3 Å and 13.0 ± 0.3 Å, respectively. Fluorescence quenching by NO (80% decrease at 0.3M NO) has no effect on the fluorescence lifetime of naphthalene, which indicates that quenching occurs in less than 5 nsec. Possible causes for the greater efficiency of fluorescence quenching by NO than by O2 are discussed. The value of R0 for naphthalene triplet-state static quenching by NO cannot be determined with certainty because of the possibility that the excited singlet state is quenched directly to the ground state. But the value of R0 for naphthalene triplet-state quenching must be less than or equal to that for fluorescent singlet-state quenching.
Ion-Pair Theory of Concentrated Electrolytes. III. Variational Principle
Authors: Stillinger Frank H. , White Ronald J.
Published: February 2004

Two major contributions are devised for that theory of concentrated electrolytes which by convention regards the ions as completely paired into uncharged dipolar “molecules.” First, a more satisfactory expression is obtained for the wavelength-dependent static dielectric “constant” ε(k). Second, a variational principle for Helmholtz free energy F is displayed whose minimization with respect to the ion-pair size distribution p(1) serves to determine both F and p(1). In anticipation of future numerical applications, a binary collision approximation is specified for the short-range interaction aspect of the functional F[p(1)].
Chlorine–Fluorine System at Low Temperatures: Characterization of the ClF2 Radical
Authors: Mamantov G. , Vasini E. J. , Moulton M. C. , Vickroy D. G. , Maekawa T.
Published: February 2004

Near-ultraviolet photolysis of matrix (N2 or Ar)-isolated chlorine trifluoride (ClF3) or mixtures of chlorine monofluoride (ClF) and fluorine at 16°K results in the production of a new infrared absorption at ∼ 575 cm−1. This band is assigned to the asymmetric stretching vibration of the chlorine difluoride (ClF2) free radical on the basis of the chemistry of the system, temperature dependence of the band intensity, and results of isotopic labeling. Much weaker bands, assigned to the symmetric stretching vibration and to the bending motion, are observed at 536 and 242 cm−1, respectively. The apex angle and force constants are calculated from the data.
Vibrational Potential Functions for CO2, OCS, HCN, and N2O
Authors: Brown Joyce E. , Parr Robert G.
Published: February 2004

For linear triatomic molecules, ABC, a vibrational potential function is proposed and tested which has the form W = W0 + W1R1 + W2R2 + W11R12 + W22R22 + W12R1R2 + W112R12R2 + W122R1R22 + WGR1R2csc(12γ), where R1 and R2 are RAB and RBC, and γ is the ABC angle. For CO2, Potential (A) has five constants: W1(= W2), W11(= W22), W12, W112(= W122), and WG, four of which are independent. In terms of these are calculated the 12 independent force constants in the most general valence-force-field potential through quartic terms. For HCN, OCS, and N2O, Potential (A) has eight constants, six of which are independent. In terms of these are calculated the 19 independent valence-force potential constants. Variations in (A) are discussed, as is its quantum theoretic basis. Physical arguments justify the form of all terms except W112 / R12R2 and W122 / R1R22. The term involving γ represents the dependence of electronic kinetic energy on bond angle.
Shock Tube Study of the Decomposition Kinetics of SO2F2
Authors: Wray Kurt L. , Feldman Eugene V.
Published: February 2004

Recent thermal decomposition studies of SF6 have led to interest in its principal oxidation product, sulfuryl difluoride. In the present study the thermal stability of SO2F2 at high temperatures has been investigated. Highly dilute SO2F2–Ar mixtures (∼ 0.1%) were shock heated in a conventional 1.5″ stainless-steel shock tube. The SO2F2 concentration was monitored as a function of time behind the incident shock wave by its infrared emission at 11.7 μ utilizing a liquid helium cooled Cu:Ge detector. The initial pressure in the shock tube was varied from 30 to 600 torr and the temperature range covered was 1900–2300°K. The monitored radiation was shown to be transparent over the range of densities employed. Effective first-order rate constants were evaluated from the logarithmic initial slopes of the radiation decay curves. For the 30-torr data, a unimolecular rate constant fit to the data is keff = 2.1 × 1011exp(− 39 200 / T) sec−1. The data are analyzed in the light of several modern unimolecular rate theories, yielding ∼ 81 kcal as the endothermicity for the reaction SO2F2+Ar→SO2F+F+Ar.
Triplet Potential for Argon
Authors: Dymond J. H. , Alder B. J.
Published: February 2004

Third virial coefficients, recalculated from pVT data, are used to determine the term in the effective argon pair potential which is linearly dependent on density, namely the averaged triplet potential. This potential is assumed to be of the form − a(T)r−n + b(T)r−6, where b(T) is derived from the known triple dipole interaction energy at large distances. Expressions for a(T) are empirically deduced for n equals 12, 18, and 24, and the resulting potentials are compared with the pair potential. Nonadditive contributions from this averaged triplet potential to the higher virial coefficients are shown to be small.
Radiation Lifetimes in Molecular and Atomic Oxygen
Authors: Copeland G. E.
Published: February 2004

Lifetimes of important states of molecular and atomic oxygen have been obtained with a cold cathode version of Holzberlein invertron.
New Equation for Surface Tension near the Critical Point
Authors: Pressing Jeff
Published: February 2004

A new modification of the Eötvös equation is proposed for the region close to the critical point. It is used in conjunction with the empirical Parachor equation to obtain reasonable values for the two critical exponents β and μ, and compute coexistence curve slopes which are in excellent agreement with experiment.
Fluorescence Efficiency and Collisional Deactivation Rate for H2 Continuum Excited by Fast Electrons
Authors: Center R. E.
Published: February 2004

The rate constant for the collisional deactivation of the H2 continuum in the near uv was measured in pure H2 at low pressures. The continuum emission was excited by 75-keV electrons and the deactivation rate constant was 1.5 ± 0.2 × 10−10 cm3/sec. An efficiency for excitation of the H2 continuum of 0.11% ± 0.03% was measured at low pressures in the absence of collisional deactivation.
Neutron Structure Analysis of Cubic CaC2 and KCN
Authors: Atoji Masao
Published: February 2004

Neutron diffraction analysis of the cubic phase of CaC2 has revealed the characteristics of the hindering potential for rotation of the C2 group, i.e., the body diagonal axes being the easiest direction for the C2 random orientation, the face diagonals being the next easiest and the cube axes being by far the hardest. A further refinement on the published neutron data of cubic KCN indicates, on the contrary to the previous analyses, a clear distinction among various orientational modes of the CN group and consequently the rotational hindering potential analogous to the CaC2 case.
Molecular Charge Distributions and Chemical Bonding. V. Molecular Excitation, Ionization, and Electron Attachment
Authors: Cade Paul E. , Bader R. F. W. , Pelletier Jocelyn
Published: February 2004

The detailed changes in the electronic charge distributions upon electronic excitation, ionization, and electron attachment are studied for selected diatomic molecules. The processes considered involve the following systems and states: O2(X 3Σg−, a 1Δg, b 1Σg+), O2+(X 2Πg), O2−(2Πg); BeH and MgH (X 2Σ+, A 2Πr); OH and SH (X 2Πi, A 2Σ+), OH+ and SH+ (X 3Σ−), and OH− and SH− (X 1Σ+). It is shown that metastable excitation in the oxygen molecule produces only a very small change in the electronic charge distribution of the system. This suggests an important role for the spin density in determining the differential behavior of these systems. The A 2Πr ← X 2Σ+ and A 2Σ+ ← X 2Πi excitations for the (BeH; MgH) and (OH; SH) pairs are examined and compared to the “active” electron approximation. The changes in binding of the system associated with these various excitations, ionization, or electron attachments is examined in terms of the partial forces exerted by the various molecular orbitals. In particular, the sharp conversion to a pronounced “ionic” molecule is evident in the BeH and MgH excitations. The A 2Πr states of BeH and MgH are as ionic as the LiH and NaH systems in their ground states. It is demonstrated that the binding ability or properties of a given orbital shows a simple graduated trend in a sequence (AB+; AB; AB−) which is not strongly dependent on the particular state symmetry of the system. The binding role assigned to a particular molecular orbital in a molecule is shown to depend on the particular state and charge situation. The implications of these results towards providing a role for the excited states and molecular ions in the theory of chemical bonding are briefly discussed.
Generalized Langevin Equations
Authors: Albers J. , Deutch J. M. , Oppenheim Irwin
Published: February 2004

A derivation is presented for a generalized Langevin equation of motion for a dynamical variable φ(R(t), P(t)) where R and P are the position and momentum of a single heavy particle in a bath of light particles. A detailed analysis is given for the conditions required for the validity of the equation. A stochastic Fokker–Planck equation is derived for the quantity D(t) = δ(R(t) − R̂)δ(P(t) − P̂) which may be used to obtain both the generalized Langevin equation for φ and a Fokker–Planck equation for the heavy particle distribution function. The correlation function for D(t) is computed and it is shown how this quantity may be used to obtain all other correlation functions of interest.
Molecular Theory of Brownian Motion for Several Particles
Authors: Deutch J. M. , Oppenheim Irwin
Published: February 2004

A molecular derivation is presented for the coupled Langevin equations that describe the motion of heavy particles in a fluid. In contrast to the case of a single heavy particle, the friction tensors which appear depend upon the instantaneous separations between the particles. A Fokker–Planck equation describing the reduced distribution function for the heavy particles is also obtained. Calculations with these equations require evaluation of the friction tensors. The friction tensors are evaluated in two ways, by an approximate macroscopic hydrodynamic calculation and an approximate hydrodynamic fluctuation calculation. Both calculations lead to identical expressions for the friction tensors which are shown to have a long-range character at large interparticle separations. Finally, it is shown that these long-range effects cancel in the calculation of the diffusion constant for each particle but remain in the calculation of the relative diffusion constant.
Proton and Fluorine Spin–Lattice Relaxation and Spin–Rotational Interaction in Liquid 1,3,5- and 1,2,4-Trifluorobenzenes
Authors: Chien Mingjien , Wade Charles G.
Published: February 2004

The proton and fluorine spin–lattice relaxation times, T1, have been measured in degassed liquid 1,3,5- and 1,2,4-trifluorobenzenes (135TFB and 124TFB) using pulsed NMR techniques at a frequency of 30 MHz. Within experimental error, the relaxation of each species could always be described with a single exponential. The data are analyzed in terms of dipolar and spin–rotational (SR) contributions to T1. The proton–fluorine dipolar interaction is theoretically approximated so that a single T1 may be used to analyze the relaxation of each nucleus. The proton relaxation was measured from the mp to 100°C and is dominated by dipolar interactions. The fluorine relaxation times, measured from − 20°C (supercooled liquid) to approximately 220°C, are dominated by dipolar interactions at the lower temperatures and by SR interactions at the higher temperatures. The inter- and intramolecular contributions to T1 were separated for F at 0°C and for H at 0 and 25°C by measuring relaxation as a function of dilution in C6D6. The intramolecular T1 values in seconds are: 135TFB:F = 33 ± 2, H = 63 ± 4 (0°) and 87 ± 3 (25°); 124TFB:F = 35.5 ± 2, H = 48 ± 3 (0°) and 55 ± 3 (25°). The dipolar correlation times obtained from H relaxation are (4.8 ± 0.2) × 10−12 sec for 135TFB and (3.1 ± 0.2) × 10−12 sec for 124TFB at 0°C. Rather inaccurate estimates of the SR contribution to fluorine T1 and the fluorine SR interaction constant (2C⊥2 + C‖2)1/2 are made and yield at 0°C the approximate values 70 sec and 2.3 kHz, respectively. The data are compared with the theories and experimental results of other investigators.
Cooperative Phenomena and the Decay of the Angular Momentum Correlation Function at Long Times
Authors: Ailawadi Narinder K. , Berne Bruce J.
Published: February 2004

A hydrodynamic solution for the decay of the angular momentum of an initially moving volume element in an otherwise stationary, compressible, viscous fluid predicts a long time decay of the angular momentum autocorrelation function which behaves as [ηst / Mρ]−(d+2)/2 where ηs is the shear viscosity, Mρ is the mass density, and d is the dimension of the system. This slow decay, which would not lead to the divergence of the rotational diffusion coefficient, or of the spin–rotation relaxation time, is caused by a vortex field which results from the interaction between a structured particle and host fluid. This result is analogous to the long time tail in the linear momentum autocorrelation function recently reported by Alder and Wainwright.
Dynamics of the Collinear H+H2 Reaction. II. Energy Analysis
Authors: McCullough Edward A. , Wyatt Robert E.
Published: February 2004

Quantitative comparisons and evaluations of the classical and quantal dynamics of the collinear H+H2 reaction are presented. The variation of classical and quantal reaction probabilities with average initial kinetic energy is shown in a series of graphs. In addition, both a quantal wavepacket and a classical ensemble are analyzed in the reactant, product, and interaction regions to determine their average kinetic and vibrational energies. Classical mechanics gives an amazingly good prediction of many detailed properties for over half of the time that reaction occurs. Included are such properties as the time dependence of the reaction probability, vibrational energy of the H3 intermediate, and the kinetic energy for motion across the symmetric stretch line on the potential surface. At late times these classical predictions show derivations from their quantal counterparts. The late time behavior of the reaction is mysterious in the sense that we do not have simple models which predict the differences between the classical and quantal calculations.
Critical Region Scaled Equation-of-State Calculations and Gravity Effects
Authors: Schmidt Hartland H.
Published: February 2004

The scaled equation of state proposed and extensively applied by Vicentini-Missoni, Levelt Sengers, and Green is expanded in forms more tractable for manipulation of higher free energy derivatives, such as Cυ, at densities away from the critical isochore. Using the xenon liquid–vapor critical region as an example, these methods are applied to the computation of the specific heat for a sample in a gravitational field. Numerical integrations for several sample depths using scaling parameter sets consistent with PVT data are presented, and sample shape effects as well as meniscus position changes with temperature are illustrated. The results are compared with experiment and those of a previous calculation using the “linear model” of the Schofield parametric equation of state. The present results differ from that computation in some respects significant for interpretation of experiments.
Crystal Field Splitting in Raman Spectra of Polytetrafluoroethylene
Authors: Boerio F. J. , Koenig J. L.
Published: February 2004

Crystal field splitting of Raman-active line group fundamentals has been observed for the crystalline phase of polytetrafluoroethylene found at temperature below 19°C. At − 180°C Raman lines near 575 and 1215 cm−1 are split into components separated by 3.5 and 4.4 cm−1, respectively. Splitting of the Raman line near 385 cm−1 increases from 5.2 cm−1 at 0°C to 6.4 cm−1 at − 180°C, indicating increasing intermolecular interaction with decreasing temperature. It is suggested that the space group of this phase is P21 and that the unit cell has dimensions a = 5.59 Å, b = 9.76 Å, c = 16.88 Å with β = 90° and contains two molecules.
Statistical Mechanics of “Waterlike” Particles in Two Dimensions. I. Physical Model and Application of the Percus–Yevick Equation
Authors: Ben-Naim A.
Published: February 2004

The Percus–Yevick equation has been adapted for a two-dimensional system of particles interacting via noncentral forces. A pair potential operating between two particles has been constructed with the intention of reproducing some properties of a sample of such particles which will be similar to the ones encountered in a real liquid water. Particularly, the open mode of packing of water molecules in the condensed state may be simulated by these particles. A numerical solution of the integral equation for the pair correlation function reveals a wealth of information on the local mode of packing of these particles, consistent with the geometries expected on qualitative grounds.
Statistical Mechanical Study of Hydrophobic Interaction. II. Interaction among a Set of M Identical, Spherical, and Nonpolar Solute Particles
Authors: Ben-Naim A.
Published: February 2004

The tendency of a set of M solute particles to adhere to each other in various solvents is examined within the framework of classical statistical mechanics. The free energy change associated with the process of bringing M solute particles from infinity to a close configuration is split into two parts:a direct work against the intermolecular potential operating among the set, and an indirect part originating from the solvent properties. Various close configurations, for which pertinent experimental results are available, are examined. It is established that the indirect part of the free energy change, referred to as the hydrophobic part, is definitely anomalous in water compared with two relatively simpler solvents. The relative probabilities of clusterization of nonpolar solutes in water and in simple solvents is found to be greater, the larger the number of solute particles.
Vapor Pressures of Liquid Ortho–Para Solutions of Deuterium; Excess Thermodynamic Functions and Intermolecular Force Constants
Authors: Meckstroth W. K. , White David
Published: February 2004

The difference in vapor pressure between equilibrium deuterium (2.15% para) and solutions of higher para composition have been measured as a function of temperature for the liquid. Several measurements in the solid state are also reported. All of the excess functions have been derived from the measurements as well as the ratio of fugacities of the pure components. The statistical mechanical treatment of Babloyantz and Bellemans [A. Babloyantz and A. Bellemans, Mol. Phys. 3, 313 (1960)] is used to account for the nonidealities of the ortho–para solutions and to obtain parameters of both the angle-dependent electric quadrupole–quadrupole interactions and the isotropic interactions represented by the Lennard-Jones function. These same parameters account for the experimental results in the case of the isotope hydrogen, indicating that the model is generally applicable.
Fluorine Relaxation in Mixtures of CF4 and Other Gases
Authors: Mohanty S. , Bernstein H. J.
Published: February 2004

The 19F spin–lattice relaxation time T1 in CF4 gas has been obtained from measurements of linewidths of NMR absorption signals at different temperatures and pressures in different solvent gases. The medium effect on relaxation can be qualitatively interpreted in terms of kinetic-theory cross sections or by the model in which a molecule behaves as a classical sphere in a viscous medium.
Configuration Interaction Studies of Ground and Excited States of Polyatomic Molecules II. The Electronic States and Spectrum of Pyrazine
Authors: Hackmeyer Melvyn , Whitten J. L.
Published: February 2004

Ab initio SCF and CI treatments of the ground state and n → π* and π → π* excited states of pyrazine, C4H4N2, are reported for the molecule in its ground state equilibrium geometry. In the case of n → π* transitions, the two symmetry combinations of nitrogen lone pair orbitals n1 and n2 are found to correspond to the description n+ ≈ n1 + n2 + λσ and n− ≈ n1 − n2 in which the n+ orbital has the higher orbital energy and is significantly more delocalized than n− by interaction with the pyrazine ring sigma system. This result leads to a significant splitting at the CI level of description of 1.4 eV between the B3u and B2g excited states which are derived from the orbital promotions n+ → π* and n− → π*, respectively. Calculated transition energies to the lowest n → π* excited states B3u3 and B3u1 of 3.56 and 4.22 eV, respectively, are in good agreement with experimental values. A low-lying B1u3(π → π*) state for which there exists indirect experimental evidence is found to occur between the B3u3 and B3u1 states. Also, an allowed transition to the B2u1(π → π*) state is calculated at 5.29 eV, slightly above the observed range of absorption. Numerous other excited states are calculated, but of these only the B1u1(π → π*) and B2u1(π → π*) states can be identified with observed transitions and in these cases the calculated transition energies are too high by approximately 2.5 eV.
Positron Annihilation in Five- and Six-Carbon Liquid Hydrocarbons
Authors: Perkal M. B. , Walters W. B.
Published: February 2004

Position annihilation rates have been measured for a series of five- and six-carbon liquid hydrocarbons containing varying degrees of unsaturation. Values for τ2, the long lifetime (in nanoseconds), and its intensity, I2 (listed in parentheses), were determined for the following compounds: trans-3-hexene, 3.35 ± 0.11(39.0 ± 4.0%); 1-hexyne, 3.42 ± 0.04(31.1 ± 2.9%); 3-hexyne, 3.13 ± 0.05(25.2 ± 2.5%); 1,3-hexadiene, 3.54 ± 0.07(30.5 ± 2.0%), trans-1,4-hexadiene, 3.29 ± 0.16(27.1 ± 3.5%); 1,5-hexadiene, 3.50 ± 0.06(30.3 ± 2.0%); 1,3-pentadiene, 3.5 ± 0.2(30.0 ± 4.5%); 1,4-pentadiene, 3.4 ± 0.2(29.6 ± 4.5%). Reduced annihilation rates, (συ)obs, were computed and compared with values predicted from index of refraction data using the methods of Gray et al. The data do not support the proposition that positron annihilation rates bear a strong fundamental relationship to indices of refraction. Partial annihilation rates for a number of functional groups and various bonds were also computed and are discussed.
Electron Paramagnetic Resonance and Optical Spectra of Pentacyanocobaltate(II)
Authors: Tsay Fun-Dow , Gray Harry B. , Danon J.
Published: February 2004

Electron paramagnetic resonance (EPR) and optical spectral studies have been carried out on the pentacyanocobaltate(II) ion in ethylene glycol–water solutions, and in electron-irradiated powder samples of K3Co(CN)6. Both EPR and optical spectra observed for the ion in the powder samples are essentially similar to those obtained from the ethylene glycol–water solutions. There was no observable linewidth variation with nuclear spin states MI, no dependence on the different solvent media used, and no dependence on the concentration ratio Co2+/CN−, in both X-band and K-band spectra. The results indicate that the structure of Co(CN)53− in solutions and in polycrystalline media is a slightly distorted square pyramid with no solvent bound in the sixth coordination site. The two strong hyperfine components with exceptionally large spacings occurring at the low-field end of the X-band spectrum are identified as the so-called angular anomalies. An effective method of simulation of the first-derivative EPR spectra of polycrystalline samples has also been developed.
Three-Body Association Reactions of NO+ with O2, N2, and CO2
Authors: Dunkin D. B. , Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: February 2004

The association of NO+ with CO2, NO++CO2+He→NO+·CO2+He, is found to occur with a rate constant 1 × 10−29 cm6 sec−1 at 197°K, decreasing at higher temperatures. When N2 or Ar are used as the third body the rate constant is about 3 times larger. The association of NO+ with O2 and N2 was found to be very much less efficient. It was found that NO+·CO2 reacts rapidly with NO to produce NO+·NO, with H2O to produce NO+·H2O, and with NH3 to produce NO+·NH3. It was found that N4+ charge transfers rapidly with O2, and N3+ reacts with O2 to produce NO+, O2+, and NO2+.
Luminescence of the Carboxyl Group
Authors: Johnson L. W. , Maria H. J. , McGlynn S. P.
Published: February 2004

A luminescence is observed from formic and acetic acids, their salts and esters. The yield of this luminescence is low (Φ < 0.01). On the basis of much circumstantial evidence, we assign this emission as a Γπ,π*3 → 1Γ1 process located on the carboxyl group. Theoretical considerations are in reasonable accord with this conclusion when it is assumed that the Γπ,π*3 state geometry is considerably different from that of Γ11. Absorption spectroscopy indicates the presence of two low-energy transitions in the formate ion; these absorption bands are quite weak and are assigned as two almost-degenerate Γn,π*1 → 1Γ1 transitions of the formate ion.
Dielectric and Pressure Virial Coefficients of Imperfect Gases. IV C2H4 and C2H4–Ar Mixtures
Authors: Bose T. K. , Cole R. H.
Published: February 2004

Results of measurements at 50°C for five mixtures and at 50, 100, and 150°C for pure ethylene are given. The pressure second virial coefficients of the mixtures are in reasonably good agreement with values predicted from combining rules and viscosity derived Lennard-Jones parameters for the pure gases. The dielectric coefficients of pure ethylene vary approximately inversely as the absolute temperature, in contrast to earlier results which showed an anomalous increase with temperature. Attributing the major contribution to dipole moments induced by ethylene quadrupole fields gives an average quadrupole moment for ethylene of 3.9 × 10−26 esu·cm2 from the pure gas data and 4.2 × 10−26 esu·cm2 from the mixture data, but it is not possible to derive values of the two independent moments from the results.
Absorption Spectrum of Cs2NpCl6
Authors: Menzel E. R. , Gruber J. B.
Published: February 2004

The absorption spectrum of single crystal Cs2NpCl6 has been investigated at 4.2, 77, and 300°K. The crystal field-split 5f3[SL]-J levels of tetravalent neptunium below 13 000 cm−1 in energy are sufficiently separated by spin–orbit interaction to permit a first-order analysis of the crystal field splitting. The crystal field splitting of the I4 and F4 states based on the octahedral symmetry of the hexachloro complex is calculated using parameters B4 = 520 and B6 = 150 cm−1. The center of gravity of the crystal field-split J levels can be compared with a theoretical “free-ion” calculation for intermediately coupled J levels using the Racah parameters E1 = 2955, E2 = 17.4, E3 = 313.8 in cm−1 and a spin–orbit parameter ζ = 1985 cm−1. In comparison with the crystal spectra of hexachloro tetravalent protactinium and uranium, the neptunium crystal-field splitting is smaller by roughly a factor of 2. This observation leads one to suspect an actinide contraction since the crystal structure is similar for all three systems.
Analysis of the Miller–Good Method for Approximating Bound States
Authors: Pechukas Philip
Published: February 2004

The “Miller–Good method” is a collection of semiclassical approximations based on a representation which emphasizes the invariance in general form of a wavefunction under changes in the Hamiltonian of which it is an eigenstate. We prove the validity of the Miller–Good representation, discuss its properties, and study the physical and mathematical content of three semiclassical schemes which employ it.
On the Time-Dependent Structure of the Currents in Non-Steady-State Nucleation Kinetics
Authors: Abraham Farid F.
Published: February 2004

Using numerical integration, we recently studied the multistate kinetics for non-steady-state nucleation in supersaturated water vapor. For cluster sizes i less than the critical size i*(i < i*), we noted a consistent “overshoot” of the currents Ii from the steady-state current I. The maximum of Ii is greater in magnitude and is reached at an earlier time ti as we examine progressively smaller clusters. In this paper, we will present a theoretical argument for the feature of the maximums in the currents.
Hyperfine Interaction and Chemical Bonding in MgH, CaH, SrH, and BaH Molecules
Authors: Knight Lon B. , Weltner William
Published: February 2004

ESR spectra of MgH, CaH, SrH, and BaH molecules in their ground Σ+2 states were measured while isolated in solid argon matrices at 4°K. The molecules were prepared by quenching metal and hydrogen atom beams in a stream of argon. g tensors and hyperfine structure (hfs) constants for interaction with H, and in the case of MgH, with 25Mg and D, were determined. For 25MgH, | Ψ (0) |2 at Mg and H nuclei were found to be 0.800(8) and 0.0663(2) a.u., respectively, in good agreement with 0.7635 and 0.03789 a.u. recently calculated by Chan and Davidson using a 953 CI wavefunction. It is evident that such elaborate calculations are necessary to obtain accurate theoretical spin densities. Hydrogen hf interaction within the group of molecules indicate less ionicity than in the corresponding diatomic fluorides although the spin density is still predominantly on the metal atoms. Metal p and d contributions are approximately derived from the observed Δg⊥ values and discussed in relation to the united-atom model.
Dynamics of the Reaction of N+ with H2
Authors: Gislason E. A. , Mahan Bruce H. , Tsao Chi-wing , Werner Arthur S.
Published: February 2004

The reaction N+(H2, H)NH+ has been investigated by measuring the velocity vector distribution of product ions formed when a collimated, mass-analyzed beam of reactant ions impinges on a target gas. In the 2.5–8.1-eV range of initial relative energies, the reaction proceeds by a direct interaction mechanism with predominant forward scattering. The forward-scattered NH+ is more excited internally than would be expected from the spectator stripping model, and the internal excitation markedly decreases as the scattering angle increases. There is evidence that at initial relative energies below 4 eV, the principal product is NH+ in the a 4Σ− state, while at initial relative energies above 6.5 eV, the X 2Π state of NH+ is formed predominantly.
Relative Rate of Deactivation of O(1D2) by Molecular Oxygen
Authors: Paraskevopoulos G. , Preston K. F. , Cvetanović, R. J.
Published: February 2004

A relative rate constant for the deactivation of O(1D2) by molecular oxygen has been obtained by two different experimental methods. In the first method, O(1D2) was generated by the photolysis of NO2 at 2288 Å, and in the second method by the photolysis of N2O at 2139 Å. The rate of deactivation was determined relative to that of reaction with N2O in the first method, and with neopentane in the second, by measuring the decrease in the yields of nitrogen and neopentanol, respectively, when O2 was added. The values obtained, expressed relative to the rate of O(1D2) reaction with CO2, kO2 / kCO2, are 0.37 and 0.28, respectively. The estimated error is about 10%–15% for both determinations. These values are in reasonable agreement with each other and with several values reported in the literature.