bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoionization of Electronically Excited Oxygen: Rate of the Reaction O2(a1Δg)+O3→2O2+O
Authors: McNeal R. J. , Cook G. R.
Published: January 2005

The photoionization spectrum of discharged oxygen has been obtained in the wavelength region 1040–1240 Å with an argon continuum light source and a 1-m Seya-Namioka scanning vacuum-ultraviolet monochromator in a discharge-flow experiment. Photoionization was detected only at wavelengths shorter than or equal to 1118.0 Å. The observed ion current is due to photoionization of metastable O2(a 1Δg), and the effects on the ion current of adding O2, N2, and O3 to the flow stream after the discharge are reported. O2 and N2 do not reduce the photoionization current except by small percentages attributable to dilution effects and, with added O2, to a slight absorption of the incident light flux. O3, however, sharply reduces the ion current and is partially decomposed by the discharged gas. These effects are attributed to the reaction O2(a 1Δg)+O3→2O2(X 3Σg−)+O(3P). Measurements of the reduction in photoionization current as a function of added O3 pressure and reaction time were made, and the rate coefficient for this reaction at room temperature has been found to be (2–3)×10−15 cm3 molecule−1·sec−1. This is a lower value than has been estimated from discharge-flow experiments in which the metastable species responsible for ozone decomposition could not be identified. Possible reasons for the discrepancy are discussed.
Resonance Quenching as a Diffusion-Type Process. I. Theory
Authors: Lavorel J.
Published: January 2005

Migration and trapping of excitons by quenching centers is described as a diffusion-type process. The corresponding initial-value problem is solved in one, two, and three dimensions, giving expressions for the fluorescence lifetime and yield. The efficiency of resonance quenching depends on the lifetime of the quenching centers, being maximum when they are permanent. The decay of excitation is faster than exponential, and its rate increases with the number of dimensions of the system. Theories of the iterated-transfer type are compared and discussed.
Hard-Sphere Model of Binary Liquid Mixtures
Authors: Snider Neil S. , Herrington Thelma M.
Published: January 2005

An equation of state [Eq. (2) of the text] which has been successfully applied to pure liquids composed of small, nonpolar molecules was generalized to the case of binary mixtures. The generalized equation was used to calculate excess thermodynamic functions for 10 equimolar mixtures, and agreement with experiment was found to be generally good. The partial molar heat of solution of gaseous neon in liquid argon was also calculated, but good agreement with experiment was not obtained in this calculation.
Study of Collision-Induced Phenomena with a Dempster Mass Spectrometer. II. Experimental
Authors: Harris Harold H. , Russell M. E.
Published: January 2005

A method for the study of collision-induced phenomena in a Dempster mass spectrometer is demonstrated. Experimental studies are made of the following reactions, and their reaction cross sections are determined at 1000 V ion-accelerating potential: Ar2++Ar→Ar++Ar+σ=3.6×10−16cm2CO++CO2→C++O+CO2σ=6.6×10−17cm2N2++N2→N++N+N2σ=3.5×10−17cm2N2O++N2O→NO++N+N2Oσ=6.3×10−17cm2CO2++CO→C++(O+)+(CO+)σ=1.4×10−17cm2.The value of 1.0×10−17cm2 for the reaction CO++CO→C++O+COwas used for calibration. In addition, the total collision cross sections for the following systems were determined: CO+in COσT=2.4×10−16cm2O+in COσT=5.0×10−17cm2C+in COσT=1.8×10−16cm2Ar+in ArσT=2.2×10−15cm2Ar2+in ArσT=1.2×10−15cm2.
Radiation Chemistry of Ice. I. Nature and pH Dependence of the Reducing Species
Authors: Schiller Robert
Published: January 2005

The decisive role of dielectric relaxation time in the electron-escape process indicated by earlier theoretical studies of the author has been investigated by scavenger experiments in normal and supercooled water and crystalline ice. In these substances of similar dielectric constants but of different relaxation times, the importance of the latter is confirmed in that no free electrons could be detected in irradiated ice samples. A semiempirical law concerning the pH dependence of H-atom yield in irradiated ice is also inferred from the experimental results.
Theory of Excitons in Liquids. III. Nonresonant Broadening of Impurity Spectra in Simple Liquids
Authors: Popielawski Jan , Rice Stuart A.
Published: January 2005

Recent studies of the molecular theory of spectral line shapes and shifts have been confined to the gaseous state. In this paper we extend a formalism, originally introduced by Fano, to the description of simple liquids. Applying ideas borrowed from the molecular theory of transport processes in simple liquids, we are able to describe the influence of the host liquid on the spectral lines of an impurity molecule in the absence of overlap between the radiating molecule and the surrounding liquid. Two effects have been found to be important: the influence of the static molecular field arising from the long-range part of the intermolecular interaction, and the influence of quasibinary hard-core encounters. The structure of the liquid has been taken into account in the local equilibrium approximation. The assumptions adopted in our presentation are discussed in detail, and the possibility of the extension of our treatment to the case of resonance broadening and the case of significant overlap between the radiating molecule and liquid surroundings is pointed out.
Reduced Density Matrices of Atoms and Molecules. II. On the N-Representability Problem
Authors: Weinhold Frank , Wilson E. Bright
Published: January 2005

For the 2-matrix of the ``double occupancy configuration interaction'' (DOCI) wavefunction described in a previous paper, the N-representability problem is stated in terms of algebraic equations relating the density-matrix elements λi, Λij, λij to the wavefunction coefficients CK. An operator formalism is developed and used to derive a number of necessary N-representability conditions for both diagonal and off-diagonal elements of the DOCI 2-matrix. These conditions consist principally of certain linear inequalities for the diagonal elements and nonnegativity requirements for the eigenvalues of certain synthetic matrices built from both diagonal and off-diagonal 2-matrix elements. A hole-particle duality is noted and used to expedite the derivations. Four special cases for which all the N-representability conditions can be explicitly given are used to show that the conditions obtained are not yet sufficient for DOCI N representability.

It is then proved that the DOCI diagonal N-representability conditions apply with equal necessity to the diagonal elements of any N-representable 2-matrix. These new necessary conditions for the general N-representability problem are given a simple and satisfying probability interpretation in terms of the Pauli exclusion principle for fermion pair distributions. Off-diagonal conditions are generated by requiring that the diagonal conditions be maintained under all possible unitary transformations of the orbital basis set. This latter procedure is illustrated by an application to the DOCI 2-matrix which accounts for all off-diagonal conditions previously obtained.
Determination of Hypervirial Operators in Perturbation Theory
Authors: Robinson Peter D.
Published: January 2005

Different formulations are discussed for the first-order correction to an eigenfunction φn of a Hamiltonian h under a perturbation V. The first formulation is −iS1φn, where S1 is a solution of the operator equation, [h, iS1]=Vod, Vod being the off-diagonal part of V in the representation {φn}. The second (due to Dalgarno) is Fnφn, where Fn is a mere function of coordinates. The third formulation (due to Sanders and Hirschfelder) is −iWnφn, where Wn is a first-order differential operator or hypervirial operator. It is stressed that, unlike Fn and Wn, S1 does not depend on the particular φn under consideration but only on h and V. Thus S1 is called a true, and Wn an apparent, hypervirial operator. True hypervirial operators are determined for a hydrogenlike atom perturbed by r−1, r, and r2, and these are compared with apparent hypervirial operators for the 1s, 2p, and 2s states.
Absorption Spectrum of RbMnF3
Authors: Mehra Anjani , Venkateswarlu Putcha
Published: January 2005

Absorption spectrum of RbMnF3 crystal has been studied at room temperature and at 77°K. The observed band positions are fitted with four parameters, B, C, Dq, and α, and the values of the parameters for the 77°K spectrum are 840, 3080, 780, and 76 cm−1, respectively. The shift in band positions on reducing the temperature is attributed to an increase in Dq. Intensities of the two sharp bands assigned to the [4A1g(G), 4Eg(G)] and 4Eg(D) levels are found to be higher than those of the broad bands. This enhancement of the intensities of the sharp bands is compared with the similar observations of earlier workers. Fine structure observed in the 4T2g(D) band is attributed to the spin-orbit splitting, and the analysis yields a value of 320 cm−1 for the spin-orbit coupling parameter ξ. Vibrational structure of the bands is analyzed by finding the vibrational modes of perovskite-structured RbMnF3.
Thermoelectric Power of Crystalline Sodium Chloride
Authors: Allnatt A. R. , Chadwick A. V.
Published: January 2005

The thermoelectric power of single crystals of pure NaCl and of SrCl2-doped NaCl was measured in the temperature range 550°–755°C using Pt electrodes and a nitrogen atmosphere. The results for the pure crystals differ significantly from previous measurements on polycrystalline material. Current theories of the heterogeneous thermoelectric power do not adequately describe the results. Part, but probably not all, of this discrepancy may be due to errors in transport numbers used, which were calculated from diffusion data. The thermoelectric power of pure NaCl is decreased by heating the crystals in oxygen-containing nitrogen.
Hartree-Fock Wavefunctions, Potential Curves, and Molecular Properties for OH−(1Σ+) and SH−(1Σ+)
Authors: Cade Paul E.
Published: January 2005

The potential curves for OH−(1σ22σ23σ21π4, X 1Σ+) and SH−(1σ22σ23σ2 1π44σ25σ22π4, X 1Σ+) have been calculated using electronic wavefunctions which are believed to be very near the Hartree-Fock wavefunctions in accuracy. Using a Dunham analysis for these two potential curves and from internal regularities of percent errors for the ground states of the first- and second-row hydrides, AH, it is predicted that for OH− 19.1≤Be≤19.4 cm−1, 3733≤ωe≤3820 cm−1, and 1.81≤Re≤1.83 bohr and for SH− 9.36≤Be≤9.54 cm−1, 2642≤ωe≤2692 cm−1, and 2.54≤Re≤2.57 bohr. The potential curves of OH− and SH− are thus closely parallel to the potential curves of OH (X 2Πi) and SH (X 2Πi), respectively. Several ways of estimating the electron affinity (E.A.) of OH and SH are presented; the most reliable values are E.A. (OH) = 1.91 eV and E.A. (SH) = 2.25 eV. These calculated results for OH− are in good agreement with recent photodetachment measurements by Branscomb. The electric dipole and quadrupole moments, the electric field gradient at the nuclei, the electronic force acting at the nuclei, and several molecular expectation values are presented as a function of internuclear separation for OH− and SH−. The relationships of these various properties to the analogous properties of the parent neutral systems [OH(X 2Πi) and SH (X 2Πi)] and the isoelectronic systems [HF (X 1Σ+) and HCl (X 1Σ+)] are discussed.
Stability of Polynucleotide Helices against Torsional Deformation
Authors: Hofelich F.
Published: January 2005

In this paper the dependence on angular coordinates of the total energy of helices with repeating monomer sequence is investigated. It is shown that for extremal total energy it is necessary to have extremal energy also for the interaction of one monomer with all the others. Conditions are given that the corresponding state be one of stable equilibrium. The results are then applied to helical arrays of dipole pairs, representing simple models for DNA polymers. It turns out that some of the observed features of polynucleotide helices are already reflected by the behavior of their dipole-dipole interaction energy as a function of the torsional angle. Hence the investigation of the behavior of the dipole-dipole interaction energy is of value for deciding in advance, whether or not an ordered secondary structure is to be expected for polynucleotides of arbitrary composition.
Wave-Interference Effects for a Forced Harmonic Oscillator
Authors: Lick Wilbert
Published: January 2005

Wave-interference effects for transitions between unperturbed states of a forced harmonic oscillator are explicitly demonstrated by comparing the exact quantum-mechanical solution for this problem with a solution which assumes transitions to the different states are independent and therefore neglects wave-interference effects.
Calculation on a Corresponding States Basis of the Volume Change on Mixing Simple Liquids
Authors: Streett W. B. , Staveley L. A. K.
Published: January 2005

There are experimental values of VE (the volume change on mixing) for eight binary liquid mixtures formed from the following substances: argon, krypton, methane, oxygen, nitrogen, carbon, and monoxide. Using a new equation of state data for the pure liquids, VE at zero pressure has been calculated for the eight systems on a corresponding states basis. Since the experimental information for liquid argon is particularly comprehensive, this substance has been taken as establishing the basic reduced-volume-reduced-temperature curve, and the intermolecular energy parameters for the other substances have been adjusted to give the best fit with this curve. The calculations have been made on the one-liquid, two-liquid (or refined average potential), and three-liquid (or separate interaction) models, and for a range of ratios of the intermolecular energy parameters of the two components of the mixture. The one-liquid model generally predicts a VE which is too positive. Of the two- and three-liquid approaches, neither can be said to be superior to the other. Both fail to give reasonable agreement with the experimental VE for the two systems with the most symmetrical molecules, namely argon-krypton and argon-methane.
Dynamic Frequency Shifts and the Effects of Molecular Motions in the Electron Spin Resonance Spectra of Dinitrobenzene Anion Radicals
Authors: Faber Roger J. , Fraenkel George K.
Published: January 2005

Electron spin resonance spectra of the m-dinitrobenzene anion radical and several of its derivatives have been examined under a variety of conditions in order to study the alternating linewidth effect and, for the first time, the associated dynamic second-order frequency shifts. More detailed information about the molecular motions was obtained in this way than is otherwise possible. The m-dinitrobenzene anion, the 3,5-dinitromesitylene anion, the 3,5-dinitrophenolate dianion, and the 3,5-dinitrobenzoate dianion radicals were obtained by electrolytic generation in solvents such as tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), and N,N-dimethylformamide (DMF). Except for the benzoate dianion in DMF, the data are well represented by a two-state model with two 14N splitting constants, aI and aII. The two different splittings probably arise because the nitro groups are complexed with the solvent or with cations. Even the spectra showing a rapid exchange between the two states have values of aI and aII that are approximately the same as those found for the single species that are obtained in the presence of alkali-metal cations, and which correspond to the static limit. The correlation times τc observed in the spectra showing the alternating linewidth effect were in the range from 0.4–0.9×10−9 sec, while those corresponding to the static limit are greater than about 10−6 sec. Spectra of the 3,5-dinitrobenzoate dianion radical obtained in DMF with and without added water could not be analyzed by a two-state model; a more appropriate model is probably one in which the carboxylate group in addition to the two nitro groups can interact with the solvent or the cations. A few spectra were carefully studied to obtain data on the g-tensor and electron-nuclear anisotropic dipolar interactions as well as those arising from modulations of the isotropic splittings, and this complete analysis made it possible to estimate values of the spectral densities for the latter interaction. In most cases studied in this way, it was found that there was complete out-of-phase correlation of the splittings at the two nitrogen nuclei.
Memory Effects and the Autocorrelation Function of a Dynamical Variable
Authors: Boon Jean-Pierre , Rice Stuart A.
Published: January 2005

In this paper we apply the theory of irreversible processes, as developed by Prigogine and co-workers, to derive the transport equation describing the time evolution of the autocorrelation function of a phase function. We show that the memory function which enters the master equation derived by Nakajima and Zwanzig (NZ) can be formally expressed in terms of the collision operator and the destruction operator which appear in the master equation of Prigogine and Resibois (PR). Because the forms of the collision and destruction operators are complex and not known in explicit terms, a simple model is used to compute the momentum autocorrelation function for a strongly coupled system. Despite the simplifications introduced by the model, amongst which is the use of an exponential repulsion between pairs of atoms, some comparison of theory and observation is valuable. Accordingly, we have made a comparison between our theoretical results and Rahman's ``experimental'' data for liquid argon. The time dependence of the destruction term is also discussed and explicitly calculated for a particular model.
Spin-Echo NMR Studies of Internal Rotation in 1,1-Difluoro-1,2-Dibromodichloroethane
Authors: Vold R. L. , Gutowsky H. S.
Published: January 2005

A spin-echo study of internal rotation in liquid 1,1-difluoro-1,2-dibromodichloroethane is reported. Carr-Pucrell spin-echo (CPSE) trains were observed from −115° to +100°C with rf pulse spacings of 0.4 to 32 msec. Modulation of the echo trains was observed at temperatures below −60°C, and the modulation frequencies were found to agree quantitatively with predictions of a general theory for the combined effects of scalar coupling and chemical exchange in spin-echo experiments. At −100°C, effects of the internal rotation are negligible and dipole-dipole interactions give different relaxation rates for fluorines in different rotamers. Above −60°C the echo trains decay exponentially. The dependence of the observed decay rates on pulse spacing was used to obtain values of the free energies of activation for exchange between rotamers and values of the fluorine chemical shifts in the different rotamers. The free energies of activation are in agreement with values obtained by steady-state NMR, and by analysis of CPSE trains at lower temperatures, but the apparent chemical shift values are about 25% too large.
Vibrational and Rotational Effects on the Nuclear Quadrupole Coupling Constants in Hydrogen, Deuterium, and Tritium Halides
Authors: Tokuhiro Tadashi
Published: January 2005

The differences of the nuclear quadrupole coupling constants in hydrogen, deuterium, and tritium halides have been studied by considering effects of vibration and rotation on the field gradient. The variation of the coupling constant can be explained by the change in size of the molecule arising from the substitution of hydrogen by deuterium or tritium.
Charge-Dipole Model of Cation Hydration
Authors: Sposito Garrison , Babcock K. L.
Published: January 2005

A systematic attempt to estimate the quantitative validity of the charge-dipole model of cation hydration is made by giving the model a quantum-theoretical structure. It is shown, in the first order of approximation, that physically reasonable results may be obtained for the proton affinity of H2O and the Gibbs potential and entropy of hydrate water. The calculated proton affinity, for example, is different by about 20% from the average of the observed values. It is concluded that because of the structural simplicity of the charge-dipole model a truly quantitative theory of cation hydration may be developed by perturbation-theoretic techniques and the incisive choice of parameters to define the multipole field of the water molecule.
X-Ray Diffraction Study of Liquid Bromine
Authors: Gruebel Robert W. , Clayton Glen T.
Published: January 2005

X-ray diffraction patterns have been obtained from liquid Br2 near the freezing point. Of the six scattering factors reported, the James—Brindley scattering factor was determined to be the one which compared most favorably with the experimental intensity. The intensity functions have been analyzed to yield electronic, atomic and molecular radial distribution functions. These show one atomic nearest neighbor at 2.3 Å and 12 molecules in two concentrations at 4.06 and 5.66 Å. The molecular pair correlation function, g(r)≡ρ/ρ0, for Br2 compares favorably to those for xenon and random-packed spheres beyond about one molecular diameter. The isothermal compressibility was determined from these data to be 14.5×10−11 cm2/dyn.
Spin-Projected and Extended SCF Calculations
Authors: Sando Kenneth M. , Harriman John E.
Published: January 2005

A comparison is presented of the energies associated with different SCF types: spin restricted, unrestricted, projected unrestricted, and extended. A method of obtaining spin-extended SCF functions is discussed. Sample calculations are done for simple hydrocarbon pi-electron radicals in the Pariser—Parr approximation, and both energies and spin densities are reported.
Fluctuations about the Approach to Equilibrium
Authors: Gordon R. G.
Published: January 2005

Mean-square fluctuations about a correlation function in its approach to equilibrium are defined and studied. For the case of a correlation function for molecular reorientation, it is shown that this time-dependent fluctuation can be evaluated by combining experimental infrared and Raman band shapes. Examples are given for liquid CO and CH4. The experiments suggest that nonequilibrium fluctuations approach their equilibrium values faster than do the corresponding average correlations.
Dissociation of H2+ by Electron Impact: Calculated Angular Distribution
Authors: Zare Richard N.
Published: January 2005

The angular distribution of products in the electron impact dissociation of H2+ has been calculated following closely the Born approximation treatment of E. H. Kerner [Phys. Rev. 92, 1441 (1953)]. When the translational kinetic energy of separation greatly exceeds the initial rotational energy of the molecule, as is normally the case, the fragments are ejected nearly along the molecular axis. For ``axial recoil'' the leading term in the differential cross section shows a cosine-squared anisotropy peaked about the momentum-transfer vector, independent of the initial rotational state of the molecule. This is in contrast to the findings of Kerner. The inclusion of higher-order terms in the differential cross section produces interference effects which shift the maximum of the angular distribution away from the momentum transfer vector towards larger angles. However, the contribution of the leading dipole term strongly overshadows the effects of these higher-order multipole terms except in certain cases quite close to threshold. When the angular distribution of products is measured about the electron-beam direction k0, rather than the momentum transfer vector K, the anisotropy assumes in the dipole limit a simple form proportional to IK(θ)=cos2θ′ cos2θ+12 sin2θ′ sin2θ, where θ′ is the angle included between k0 and K. Upon integrating over all possible values of K for a fixed electron-impact energy, the form of the anisotropy is found to be a maximum close to threshold, but is first degraded and then reversed in sense as the bombarding electron energy is increased. In the high-energy limit, however, the angular distribution does not approach a sine-squared anisotropy, but rather a limiting form is asymptotically approached corresponding to an average θ′ of about 68°. Comparisons are made with the related experimental studies of G. H. Dunn and L. J. Kieffer [Phys. Rev. 132, 2109 (1963)] on the dissociative ionization of H2.
Viscosity of Hydrogen—Nitrogen and Hydrogen—Ammonia Gas Mixtures
Authors: Pal Arun K. , Barua A. K.
Published: January 2005

The viscosity of the binary gas mixtures H2–N2 and H2–NH3 has been measured in the temperature range 33°—200°C and at pressure below 10 cm Hg, by using a precise oscillating-disk method. The data have been utilized to calculate interdiffusion coefficients for these systems.
Mixing Properties and Radial Distribution Functions of Binary Liquid Mixtures
Authors: Chung H. S. , Espenscheid W. F.
Published: January 2005

A generalization of the Dahler—Hirschfelder theory to binary liquid mixtures is presented. The purpose is to delineate the basic difficulties involved in the construction of a molecular theory of mixtures by examining this generalized theory and appraising its range of applicability to real systems. The thermodynamic properties and radial distribution functions of many binary mixtures of Lennard-Jones molecules are calculated and the effects on the mixing behavior of variations in the potential parameters and of deviations from the usual combining rules are considered. The influence of these factors is so pronounced that accurate estimates of the mixing properties are possible only under optimum conditions. The task of formulating a quantitative statistical theory of mixtures remains quite formidable and the final solution of this problem appears to be remote.
Theoretical Study of Triplet—Triplet Absorption Spectra. I. Alternant Hydrocarbon Molecules
Authors: Orloff Malcolm K.
Published: January 2005

The self-consistent-field molecular-orbital method of Pariser, Parr, and Pople is utilized to calculate the transition energies and oscillator strengths of triplet—triplet absorption bands in 12 alternant hydrocarbon molecules. The agreement between theory and experiment for the energy of the most intense triplet—triplet absorption band in the visible region of the spectrum is of the order of 0.1 eV. The positions of the weaker bands are calculated less reliably. The axis of polarization calculated for the triplet—triplet bands agrees with experiment in the few cases where such measurements have been made. In addition, the locations of several triplet—triplet bands not yet observed in the infrared and ultraviolet regions are predicted.
Frenkel Exciton Selection Rules for k≠0 Transitions in Molecular Crystals
Authors: Colson S. D. , Kopelman R. , Robinson G. W.
Published: January 2005

Three types of dipole selection rules are proved for k≠0 in a restricted Frenkel exciton limit. They are: (1) Δk=0; (2) general selection rules based on interchange symmetry; and (3) the g↔u selection rule for centrosymmetric crystals. Even though the latter two selection rules are generally valid only for special values of k, and in particular for k=0, they can be shown to be valid for all k in crystals where restrictions are placed on the magnitude of interactions between certain translationally equivalent molecules. For benzene and naphthalene, and probably for many other organic crystals, the translationally equivalent interactions that ruin the selection rules are nonnearest neighbors. Evidence suggests these in some cases are small, in which event the selection rules are excellent approximations. It is also shown that the transition matrix element in this restricted Frenkel limit is k-independent, a fact that is important in analyzing the intensity distribution of band←band transitions in terms of the density-of-states function. Inability to detect a u←u, band←band transition in crystalline benzene is consistent with the theoretical results.
Ethylene—Oxygen Reaction in Shock Waves
Authors: Gay I. D. , Glass G. P. , Kern R. D. , Kistiakowsky G. B.
Published: January 2005

The reaction of ethylene with oxygen in mixtures dilute in neon or argon was studied in shock waves by several methods. Observations of CH (A2Δ→X2π) chemiluminescence and of total chemi-ionization behind incident waves revealed induction periods followed by exponential rise of the signals. The former, for both phenomena, are representable by the equation log10(ti[O2])=−11.23±0.20+(23 110±1610)/4.58Tand the latter by log10(τ[O2])=−12.07±0.15+(23 950±1270)/4.58T.The units for both equations are seconds·moles liter−1. A time-of-flight mass spectrometer was used to measure the formation of neutral and chemi-ion product species behind reflected waves. The initial rate of formation of H2O was found to be exponential in time and the time constants were found to be consistent with the results obtained for chemiluminescence and chemi-ionization. Acetylene was found to be formed in large yields concurrently with H2O and CO and to be subsequently rapidly oxidized, except in mixtures deficient in oxygen. Chemi-ionization follows the formation of observable concentrations of acetylene. Chemi-ion mass spectra and yields are very similar to those observed in a previous study of the oxidation of acetylene. A tentative reaction scheme is proposed which involves a branching chain oxidation of ethylene, the rate determining step being C2H3+O2→C2H3O+O; the products are C2H2, H2O, CO, and H2. Chemi-ionization and CH chemiluminescence are attributed to the subsequent chain oxidation of acetylene.
Thermodynamic Properties of Octafluoropropane from 14°K to Its Normal Boiling Point. An Estimate of the Barrier to Internal Rotation from the Entropy and Heat Capacity of the Gas
Authors: Pace E. L. , Plaush A. C.
Published: January 2005

The heat capacity of octafluoropropane has been measured from 14°K to its normal boiling point of 236.42°K for a sample of greater than 99.99 mole % purity. The following heats of transition and transition temperatures were found: Crystal I—Crystal II, 849.8 cal/mole, 99.37°K; Crystal I—liquid, 114.1 cal/mole, 125.46°K; and liquid—vapor (1 atm), 4723 cal/mole, 236.42°K. The vapor pressure up to 1 atm pressure is represented by the equation log10Pmm=20.85981−(1584.677/T)−4.750509 log10T,and the density of the liquid between 197° and 234°K by the equation d(g/ml)=2.471−0.003628T.

The value of the entropy of the ideal gas at 1 atm pressure at the normal boiling point calculated from the calorimetric data is 88.75 cal/ (mole·°K).

An average potential barrier of 3300 cal/mole restricting the rotation of the trifluoromethyl groups is estimated from the entropy computed from molecular data. A reasonable but not an entirely satisfactory interpretation of the heat capacity of the gas is also obtained with a barrier of the above order of magnitude.
Thermodynamic Properties of Hexafluoroacetone from 12°K to Its Normal Boiling Point. An Estimate of the Barrier to Internal Rotation from the Entropy of the Gas
Authors: Plaush A. C. , Pace E. L.
Published: January 2005

The heat capacity of hexafluoroacetone has been measured between 12°K and the normal boiling point of 245.87°K for a sample of greater then 99.99 mole % purity. The molar heat of fusion at 147.70°K was found to be 2003.5 cal/mole. The molar heat of vaporization at 245.87°K was found to be 5166 cal/mole. The vapor pressure of the liquid to 1 atm pressure is represented by the equation log10Pmm=28.35833−(1963.631/T)−7.316256 log10Tand the density of the liquid between 199° and 243°K by d(g/ml)=2.386−0.003491T.The entropy for the ideal gas at the normal boiling point was found to be 89.63 cal/ (mole·°K) from the calorimetric data. The calorimetric entropy is shown to be reasonably interpreted in terms of existing spectroscopic and molecular data and a potential barrier of 1470 cal/mole restricting the rotation of the trifluoromethyl groups.
Calculations of Electric Field Gradients in H2+ and H2 Using Single-Center Wavefunctions
Authors: Henderson Richard C. , Ebbing Darrell D.
Published: January 2005

Calculations have been made of the electric field gradient at the proton in H2+ and H2 with single-center wavefunctions, where the expansion center is at one of the protons, or at the midpoint. In all cases, the electric field gradients are in good agreement with experiment; although, for a given amount of computational effort, the midpoint expansions appear superior. Apparently this is due, in part at least, to the fact that a large contribution to the electric field gradient comes from the electrons in the bonding region.
Adsorption of Oxygen on Tungsten at Temperatures from 300° to 850°K
Authors: Singleton J. H.
Published: January 2005

The adsorption of oxygen has been studied on a polycrystalline tungsten ribbon at temperatures from 300° to 850°K. Two types of tungsten surface structure are distinguishable by their adsorption and desorption behavior. At 300°K, adsorption on either type of surface occurs into a single phase, but, at higher temperatures, to a maximum of ∼765°K, additional adsorption occurs, with an energy of activation of ∼0.25 eV. This process probably involves a reconstruction of the tungsten surface rather than the adsorption into a pre-existing set of sites. Limited measurements at temperatures between 800° and 1000°K are consistent with the model of a solution process restricted to the surface layers of the tungsten. The removal of adsorbed oxygen, in a high-temperature flash, occurs only by oxide evaporation below ∼1650°K and by evaporation of both an oxide and oxygen, above this temperature.
Kinetics of the Excited Singlet and Triplet States of Vapor-Phase Phenanthrene
Authors: Powell G. L.
Published: January 2005

The lifetime, τ=1/k, of the first excited singlet state of vapor-phase phenathrene has been measured as a function of pressure and excitation wavelength. Excitation in the first singlet absorption band (3400–3100 Å) resulted in τ=50±2 nsec and excitation in the second singlet band resulted in τ=45±2 nsec. The singlet-to-triplet intersystem-crossing efficiency, ΦST=kST/k, was measured and found to be ΦST=0.88±0.05. From the measured absorption and emission spectra, the fluorescence efficiency, ΦF=kF/k, was calculated to be ΦF=0.07. Internal conversion from the lowest excited singlet state to the ground state was shown to be very inefficient (ΦIC<0.05). All parameters were found to be independent of phenanthrene pressure. It is also shown that triplet—triplet annihilation to give delayed fluorescence is at least 20 times more efficient than any other second-order triplet process. The first-order triplet decay constant β was found to be β=3.3×102 sec−1.
Relationships between AB2 and HnAB2 Molecular Spectra and Geometry: Accurate SCF MO and CI Calculations for Various States of HCOO−
Authors: Peyerimhoff Sigrid D.
Published: January 2005

A close relationship between the geometry of formate ion in various electronic states and that of isoelectronic-symmetric AB2 molecules is demonstrated by means of accurate SCF MO calculations for ground and certain excited states of HCOO− which are compared to corresponding calculations for O3. Transition energies between several states of HCOO− are calculated within a limited CI treatment and their relation to spectral lines of corresponding AB2 molecules is discussed. Such comparisons suggest that existing relationships between the geometry of AB2 molecules can be extended effectively to the study of isoelectronic HnAB2 systems of related symmetry even though these molecules may otherwise bear little similarity to the triatomic systems.
Correlation Energy and Molecular Properties of Hydrogen Fluoride
Authors: Bender Charles F. , Davidson Ernest R.
Published: January 2005

A natural-orbital—configuration-interaction calculation has been carried out on the ground state of the hydrogen fluoride molecule at the experimental equilibrium internuclear separation (1.7328 a.u.). A non-relativistic energy of −100.2577 a.u. was obtained with 39 configurations. Individual pair correlation energies totaling to over 80% of the total correlation energy were obtained by considering double excitations of each pair.
Rotational Isomerism in Bromoacetone and Fluoroacetone
Authors: Crowder G. A. , Cook Bobby R.
Published: January 2005

Infrared spectra in the region 60–4000 cm−1 were obtained for bromoacetone and fluoroacetone for the vapor and liquid (or solution) states and for the solid state in the region 600–4000 cm−1. Spectra in the region 300–4000 cm−1 were obtained for solutions in carbon tetrachloride and acetonitrile. The spectra show that both these compounds exist as mixtures of rotational isomers, and that the less polar form is present in much higher amount in the vapor state than the more polar form. For bromoacetone, the more polar form is more stable in the liquid state, and is the only form present in the solid. For fluoroacetone, the two forms have about the same energy in the liquid, and both forms are present in the solid.
γ Radiolysis of Liquids at High Pressures. III. Aqueous Solutions of Sodium Bicarbonate
Authors: Hentz Robert R. , Farhataziz  , Milner David J. , Burton Milton
Published: January 2005

The γ radiolysis of deaerated aqueous solutions containing sodium bicarbonate and either glucose or isopropanol has been studied at ∼20° in the applied pressure range 0 to 7 kbar. For 0.05M bicarbonate and 0.036M isopropanol, G(H2) increases from 0.89 to 2.43 as applied pressure increases from 0 to 6.9 kbar. A 100-fold change (0.005–0.5M) in bicarbonate concentration has little or no effect on the pressure dependence of G(H2). Because primary yields are invariant over the pressure range studied, the results are interpreted in terms of an effect of pressure on the competition between Reactions [2] and [3]eaq−+CO2→CO2−,eaq−+HCO3−→H+CO32−,with Reaction [3] followed by Reaction [4]H+RH→R+H2.Such an interpretation gives a difference in activation volumes of Reactions [2] and [3] as ΔV2‡—ΔV3‡≈18.4 ml mole−1 and a specific rate k30≈6×105M−1· sec−1 at atmospheric pressure. Assumption that Reaction [2] is diffusion controlled permits estimation of ΔV2‡≈1.6 ml mole−1, from the pressure dependence of water viscosity. Thus, ΔV3‡≈−16.8 ml mole−1. The latter value, in turn, yields an estimate of V̄(eaq−) in the range −10.9 to −6.5 ml mole−1 relative to V̄(H+)=0. Use of an absolute value of V̄0(H+)=−5.4 ml mole−1 gives an absolute value of V̄0(eaq−) in the range −5.5 to −1.1 ml mole−1. Approximate equality of the values for V̄0 of the electron and of the proton is consistent with their having a negligible intrinsic volume and approximately equal electrostriction volumes.
Proton Spin—Lattice Relaxation Temperature Dependence in Ammonium Bromide
Authors: Woessner D. E. , Snowden B. S.
Published: January 2005

The lambda transition at 234.5°K in ammonium bromide has been detected by proton spin—lattice relaxation temperature dependence measurements. There is a small but detectable change in T1 at the lambda point. In order to obtain the maximum detail in this temperature region, a special probe was designed to minimize temperature gradients in the sample. Use of this probe allows evaluation of the change in T1 at the transition and determination of the apparent activation energy immediately below the transition. The previously reported x-ray, dilatometric, extensometric, and acoustical data are best interpreted in terms of a conceptual picture of domains defined by the orientation of tetragonal axes in the region immediately below the lambda point and the indistinguishability of the domains above this temperature. The τc data are consistent with this concept. The degree of order seems to be affected by the orientations of the tetragonal axes in the domains. Comparison of the acoustical data and the τc data suggests that the elastic constants are much more dependent on the electrostatic changes due to the volume changes than is the temperature dependence of τc. The latter seems to depend mainly on the degree of order in the crystalline lattice.
Mössbauer Hyperfine Interactions in Sodium Nitroprusside Single Crystals
Authors: Danon J. , Iannarella L.
Published: January 2005

The Mössbauer absorption spectrum of 57Fe in single crystals of Na2[Fe(II)(CN)5NO]·2H2O has been studied. The angular variation of the ratio of intensities of the quadrupole-splitted lines with the incident radiation has been measured at different crystal orientations. The results may be satisfactorily interpreted by considering the detailed symmetry of the crystal and the effects of the anisotropy of the recoilless absorption probability. It was found that an axially symmetric field gradient with its principal axis oriented along the Fe–NO directions, couples with the nuclear quadrupole moment of 57Fe giving a positive interaction with the value eq=+0.585×1018 V/cm2. This field gradient is assumed to originate from unbalanced d-electron density and the electronic population calculated for the molecule agrees with that obtained by molecular-orbital methods. The large total s-electron density at the 57Fe nucleus measured by the isomer shift is quantitatively related to the effective 3d-electron population and to the 4s partial occupation. Estimates of the 4s density also agree with that reported from molecular-orbital calculations.
SCMO Calculations on the Tetramethyl-p-Phenylenediamine System
Authors: Monkhorst Hendrik J. , Kommandeur Jan
Published: January 2005

SCMO calculations in the PPP approximation were carried out on the tetramethyl-p-phenylenediamine (TMPD) system. Comparison with experiment was made for TMPD, TMPD+, and TMPD++. In general good agreement for one set of parameters was obtained.
Magnetic Transition of Wurster's Blue Perchlorate. I. The Low-Temperature Phase
Authors: Pott Gerard T. , Kommandeur Jan
Published: January 2005

Evidence is given for the low-temperature phase of Wurster's blue perchlorate being built up of bipositive ions and neutral molecules, the high-temperature phase having undergone disproportionation according to 2 TMPD+→TMPD+TMPD++. The electronic as well as the ESR spectra can be explained on this basis. The actual transfer of charge required in the disporportionation can be observed as a conductivity peak in the transition range.
Magnetic Transition of Wurster's Blue Perchlorate. II. Theoretical Considerations
Authors: Monkhorst Hendrik J. , Pott Gerard T. , Kommandeur Jan
Published: January 2005

A theoretical discussion is given of the low-temperature phase of Wurster's blue perchlorate. The suggested disproportionation of the TMPD+ ions can be simulated by the introduction of an inequivalence potential in an SCMO calculation of the ionic dimer. The value of this potential, as well as its consequences for the electronic absorption spectra is discussed. A calculation of the energy difference between high- and low-temperature phase is given suggesting this difference to be almost zero, thus making a phase transformation possible.
Crystal Structure of Tetramethylammonium Fluoride Tetrahydrate
Authors: McLean W. J. , Jeffrey G. A.
Published: January 2005

Tetramethylammonium fluoride tetrahydrate is tetragonal, space group I41/a with a=10.853 and c=8.065 Å at −26°C. The crystal structure was determined from the crystal data and the Patterson synthesis and refined by least squares. It has a hydrogen-bounded ionic/water framework composed of four-coordinated fluoride ions and three-coordinated water molecules. The tetramethylammonium ions are in voids within this framework.
Measurement of the Frequency of Torsional Vibration in the Ethane Molecule
Authors: Strong K. A. , Brugger R. M.
Published: January 2005

The direct excitation of the torsional vibration of the two methyl groups in ethane was observed in a slow-neutron inelastic-scattering experiment. Theoretical curves fit to the data indicate that the energy of transition from the zero to first excited state of this oscillation is 0.0332 eV (268 cm−1) if the potential is assumed to be harmonic or 0.0344 eV (277 cm−1) if the potential is assumed to be represented by ½V0(1+cos3θ). To observe the transition, the scattering at small angles was observed through an evacuated scattering chamber and with careful consideration of multiple neutron scattering.
Fate of Triplet Difluoromethylene
Authors: Johnston Timothy , Heicklen Julian
Published: January 2005

Triplet CF2 was produced by the reaction of ground-state oxygen atoms with C2F4 at room temperature. This radical can react with O2 or undergo self-annihilation to form singlet CF2: CF23+O2→CF2O2;2CF23→C2F4*→2CF21,where the superscripts 1 and 3 refer to singlet and triplet. The ratio ke/kf1/2 was estimated to be about 12 (liter/mole·sec)1/2.
Diffusion Cloud-Chamber Investigation of Homogeneous Nucleation
Authors: Katz J. L. , Ostermier B. J.
Published: January 2005

The critical supersaturations for the homogeneous nucleation of ethanol, methanol, hexane, and water were experimentally determined in the temperature range 235° to 295°K using a thermal diffusion cloud chamber. The design, construction, and operation of the chamber are described. A computer solution of the heat and mass flux equations determines the variation of pressure and temperature as a function of chamber height. The determination of the experimental critical supersaturation from chamber conditions is described and a comparison made with the values calculated from the Becker-Doering, Volmer, Zeldovich equation. Good agreement (usually within 5%) is obtained for ethanol, methanol, and hexane over a 60°K temperature range. Experimental difficulties limited the water data to a temperature range less than 15°K and agreement to within 15%.
Intermediate Excitons in Molecular Crystals: A Study of the Excited States of Crystalline Iodine
Authors: Hillier Ian H. , Rice Stuart A.
Published: January 2005

The spectrum of crystalline I2 is interpreted in terms of intermediate excitons represented by configuration mixing of neutral excitons and charge-transfer excitons. The spin—orbit splitting in the crystal is represented in terms of the spin—orbit states of the free molecule. Using a core approximation analogous to the Goeppert-Mayer—Sklar procedure, semiquantitative calculations are made. When a reasonable value is assigned to the polarization energy of an ion pair in the crystal, reasonable agreement between calculation and experiment is obtained.
Dynamical Effects in Triplet ESR Spectra of Solid Solutions. II. Correlation of the Rate of Intermolecular Triplet Excitation Transfer with the Line Shape of the ESR Spectrum of a Solution of Aromatic Phosphorescent Hydrocarbons in a Rigid Matrix
Authors: Kottis Philémon
Published: January 2005

The stochastic theory of resonance absorption, as formulated by Anderson, is used to simulate the effect of excitation transfer observed by de Groot and van der Waals in the ESR spectra of a number of aromatic hydrocarbons excited to the lowest triplet state in a glassy solution. The single-transition correlation function φ(t) of Anderson is modified to include the important nonsecular contribution of the dipolar interaction. In a ``three-site'' case, the latter approximation reduces a 9×9 matrix to a 3×3 matrix problem and allows actual calculations. ``Δm=1'' and ``Δm=2'' line shapes of an assembly of randomly oriented molecules of tribenzotriptycene are calculated for a set of transfer rates from 0 to 1011 sec−1. These simulations are in good agreement with the experimental ESR spectra recorded at 77° and at 20°K and allow a fair derivation of the transfer rate vs temperature. The absorption formular in a ``three-site'' case has been fitted into a computer program, the input data being the zero-field splitting constants, the angles characterizing the mutual orientation of the sites and the triplet-excitation transfer rate k.