bluuebunny/crossref_metadata_2025 huggingface dataset:
Gaseous Diffusion: The Systems He–Kr, Ar–Kr, and Kr–Xe
Authors: Malinauskas A. P.
Published: January 2005

Gaseous diffusion coefficients are reported for the systems He–Kr, Ar–Kr, and Kr–Xe. The results were obtained over the temperature range 0° to 120°C with an apparatus of the Ney—Armistead type and can be described by the following expressions: He–Kr, log10D12=1.688 log10T−4.3844; Ar–Kr, log10D12=1.917 log10T−5.6017; Kr–Xe, log10D12=1.858 log10T−5.7108, wherein the diffusion coefficients have been reduced to 1 atm pressure and refer to diffusion involving only trace quantities of the heavier component. The experimental data compare favorably with results derived from viscosity measurements, but show deviations for thermal-conductivity-derived values, which appear to become progressively larger as the mass difference of the gas pair increases.
Reactions of Nitrogen—Hydrogen Radicals. II. Decomposition of Hydrazine by Hydrogen Atoms
Authors: Ghosh Pradip K. , Bair Edward J.
Published: January 2005

The luminescent reaction of hydrazine with atomic hydrogen was studied in flowing gas systems. The emission is due to NH2 radicals apparently produced by the process N2H4+H→NH3+NH2(2A1)* . Estimates of the emission quantum yield show that this is a relatively minor process. Accepting the conclusion of Schiavello and Volpi that the major decomposition process is N2H4+H→N2H3+H2 with a rate, 3.5×108 exp (−2000/RT) liters/mole·sec, the temperature dependence of the emission intensity is interpreted in terms of these competing processes to give a rate 1.2×105 exp (−2600/RT) liters/mole·sec for the emission reaction. The emission spectrum appears to have a short wavelength limit corresponding to 50.7 kcal, yielding a value for the heat of formation of NH2 consistent with other determinations.

The absorption spectrum shows an unexpectedly high concentration of NH2 radicals in the reaction zone. This is consistent with the other known facts if the process, N2H3+H→2NH2, becomes important when the [H]/[N2H4] ratio is large.
Microwave Determination of the Centrifugal Distortion Constants of the Methyl-d3 Halides
Authors: Garrison Allen K. , Simmons James W. , Alexander Chester
Published: January 2005

Measurements of pure rotational transitions ranging from J = 0 — 1 up to J = 8 — 9 have been carried out for the series of deuterated methyl halides listed below in a frequency range from 12 to 152 GHz. Resulting values of the rotational and centrifugal distortion constants B0, DJJ, and DJK, respectively, are: for CD335Cl, 10 841.91 MHz, 10.84 kHz, and 102.7 kHz; for CD337Cl, 10 658.47 MHz, 10.56 kHz, and 99.46 kHz; for CD379Br, 7714.63 MHz, 5.83 kHz, and 63.56 kHz; for CD381Br, 7681.23 MHz, 5.86 kHz, and 63.27 kHz; for CD3127I, 6040.31 MHz, 3.59 kHz, and 48.32 kHz. The quadrupole coupling constant eqQ for the halide nucleus in each of these molecules is, respectively: −74.6, −58.8, 575.7, 480.9, and −1929 MHz. Comparison of the above centrifugal distortion constants with those calculated from known force constants is made.
Absorption Spectra of Gaseous NdBr3 and NdI3
Authors: Gruen D. M. , DeKock C. W.
Published: January 2005

Absorption spectra have been obtained of gaseous NdBr3 and NdI3 in the range 4000–25 000 cm−1 between 1000° and 1200°C. Spectra of solid and liquid NdI3 near the melting point have also been measured.

The most prominent feature of the gaseous spectra is a complex band located between 16 000–17 000 cm−1 with oscillator strengths of 3.3×10−4 and 5.3×10−4 for NdBr3 and NdI3, respectively. The band is assigned to the hypersensitive transition 4I9/2—4G5/2.

The oscillator strength of this transition in the vapor molecules is 10–50 times greater than in the solution systems studied by Carnall, Fields, and Wybourne. Various intensity mechanisms are discussed and it is concluded that the vibronic mechanism gives order-of-magnitude agreement with results. Judd's proposal that the parameter T2 is particularly sensitive to environment is borne out by the results on the vapor spectra.
Quantum Theory for the Unimolecular Rate Constant
Authors: Thiele Everett
Published: January 2005

A formal quantum theory for the unimolecular rate constant is presented. This theory is an elaboration on an earlier paper by Wilson and Thiele. The theory treats the unimolecular breakdown quantum mechanically, but retains two classical-like assumptions concerning the collision mechanism and the criteria for reaction. A model calculation suggests that these assumptions can be used if ω≪kT/h. Some arguments are also presented which suggest this same limit of applicability for the general theory.
Photoionization of n-Butane at 1067–1048 Å. Decomposition of the Parent Ion and Superexcited Molecule
Authors: Ausloos P. , Lias Sharon G.
Published: January 2005

n-C4H10, n-C4D10, CD3CH2CH2CD3, and C4D10—C3H6 mixtures have been irradiated in the presence of oxygen with the argon resonance lines at 1067 and 1048 Å. On the basis of saturation-ion-current measurements, the ionization-efficiency ratios ηC4D10/ηNO and ηC4H10/ηNO were estimated to be 0.480±0.005 and 0.465±0.005, respectively. It is demonstrated that at the argon-resonance lines the C4H10+ ion undergoes fragmentation according to the following two processes: C4H10+→C3H7++CH3→C3H6++CH4.The isotopic analysis of the propane fraction formed in the irradiation of n-C4H10–n-C4D10–O2 mixtures indicates that the propyl ion which reacts with n-butane to form propane by a H− or D− ion transfer has the sec-propyl ion structure. It is further shown that, in agreement with recent studies on ion—molecule reactions, the C3H6+ ion also reacts with C4H10 to form C3H8 (H2− transfer). The yield of the parent ion was estimated by making use of the recently established H2-transfer reaction: C4H10++C3D6→CD3CDHCD2H+C4H8+.

The fragmentation of the butane parent ion is strongly quenched by an increase in the pressure of butane, or upon addition of an inert gas. The following approximate relative efficiencies for the quenching of the fragmentation of the excited C4D10+ ion are obtained: He, 1; N2, 5; C4D10, 35. It is also noted that the fragmentation of the C4D10+ ion is more readily quenched by collision with He than that of the C4H10+ ion by about a factor of 5.

The fragmentation of the neutral excited molecule has been examined briefly on the basis of the isotopic analysis of products formed in the photolysis of CD3CH2CH2CD3—O2 mixtures at 1470, 1236, and 1067–1048 Å, and of those formed in the photolysis of C4D10—H2S mixtures at 1236 Å. It is concluded that the modes of decomposition of the superexcited molecule are essentially identical to those observed for molecules excited at photon energies below the ionization energy, although the elimination of an H2 molecule or an alkane may be of lesser importance at the shorter wavelength.
Ground State of Bis(Acetylacetonato) Copper (II)
Authors: Allen Harry C.
Published: January 2005

Existing data on the polarized crystal spectrum of bis (acetylacetonato) copper (II) are interpreted. Through the use of a lower molecular symmetry than had previously been used, it is possible to present an interpretation consistent with that for the spectra of other bis copper (II) chelates.
Reactions of C3H6+ with C3 and C4 Paraffins
Authors: Sieck L. Wayne , Futrell J. H.
Published: January 2005

Rate constants for H− and H2− transfer from C3 and C4 paraffins to propylene and cyclopropane molecular ions have been determined for ions of low translational energy at the ionization threshold of C3H6+. The results indicate that an increase in KH− is accompanied by a compensating decrease in KH2− and vice versa, such that the total reactivity of C4 structural isomers is invariant. By using selectively labeled compounds, it was possible to derive transfer probabilities for the various substituent sites on the normal butane carbon skeleton. Evidence is also presented which suggests that cyclopropane molecular ions do not assume the propylene-ion structure prior to or during reaction with C4 paraffins. The results of the present investigation are compared with some complementary data obtained from radiolytic and photolytic systems at much higher pressures.
Mathematical Properties of Frost's Local-Energy Method
Authors: Stanton Richard E. , Taylor Robert L.
Published: January 2005

Frost's local-energy method is analyzed in two different ways. An exact, trigonometric solution is carried out for the two-dimensional problem. The more general problem is treated by perturbation theory.

It is shown that not all solutions of the local-energy equations correspond to minimum variance. Some correspond to maximum variance, others to a saddle point on the variance hypersurface. The number of minimum variance solutions is equal to the number of basis functions when the latter are well chosen, but may otherwise be smaller.
Development of a High-Pressure Capillary-Tube Viscometer and Its Application to Methane, Propane, and Their Mixtures in the Gaseous and Liquid Regions
Authors: Giddings John G. , Kao James T. F. , Kobayashi Riki
Published: January 2005

A versatile absolute capillary-tube viscometer has been developed and applied to measure the viscosity of methane, propane, and four selected mixtures of the two from 100 (6.8 atm) to 8000 psia (544.4 atm) and temperatures from 40° (4.44°C) to 280°F (137.78°C). The reproducibility of the data, excluding the critical regions, was 0.25%. The data for the pure components are critically compared with values available in the literature.

Within the experimental limits of this study, it has been found that, for each pure component and mixture studied, the residual viscosity, the viscosity at some pressure and temperature less the dilute-gas viscosity at that temperature, is a unique and continuous function of the density.
Perturbation—Variation Approach to Optical Rotatory Power
Authors: Chang Tai Yup
Published: January 2005

A perturbation—variation approach to the optical rotatory power of molecules for calculating the rotatory parameter through the first order of the badness of the molecular wavefunction is presented. This should allow for all the significant terms and all the important transitions in the spectral formula.
Ion—Molecule Reactions by a Photoionization Mass Spectrometer. II. Butene−1, Butene−2, and Isobutylene
Authors: Koyano Inosuke
Published: January 2005

Ion—molecule reactions of the parent ions of butene−1, butene−2 (cis and trans), and isobutylene with their corresponding neutral molecules have been studied by a photoionization mass spectrometer. Seven reactions of butene−1 parent ions, three of butene−2, and three of isobutylene have been identified and their cross sections determined. Parent-plus-one and parent-minus-one reactions occurred more or less in all olefins studied, among which C4H9+ formation in isobutylene had a much larger cross section than others. Butene−2 parent ions were highly unreactive compared with the other two olefin ions, and their cis and trans isomers showed the same reactions with exactly the same cross sections.
Influence of Molecular Rotation on the Viscosity of Liquids
Authors: Davies D. B. , Matheson A. J.
Published: January 2005

Although certain liquids show Arrhenius viscosity behavior over the whole liquid range, most liquids have a substantial non-Arrhenius range in which their viscosity is described by the free-volume equation. In a few supercooled liquids, there are two distinct non-Arrhenius regions. From a calculation of the volumes required for free rotation of molecules in a liquid, it is shown that the transition from one type of dependence of viscosity on temperature to another is due to the restriction of the rotation of molecules in the liquid. In the Arrhenius region, molecules are free to rotate many times about at least two axes during the time between translational jumps. In the higher temperature non-Arrhenius region, molecules are able to rotate about only one axis, while in the lower temperature, non-Arrhenius region rotation occurs primarily as a result of molecular translational motion.
Effect of Pressure on the Lattice Parameters of Iodine, Stannic Iodide, and p-Di-iodobenzene
Authors: Lynch R. W. , Drickamer H. G.
Published: January 2005

The effect of pressure to over 200 kbars has been measured on the lattice parameters of iodine, stannic iodide, and of p-di-iodobenzene. All three have a large component of van der Waals binding and each exhibits a compressibility which decreases with increasing pressure. On the basis of the estimated change in distances in the crystal, the approach to the metallic state in and perpendicular to the ac plane in iodine is explained. The approach to the metallic state and possible bond deformation in SnI4 is discussed. Possible molecular realignments in p-di-iodobenzene are proposed. The results on molecular crystals are contrasted with the behavior of TlI previously published.
Properties of the 1Σg+ State of H2 Calculated from an Accurate Adiabatic Potential
Authors: Cashion J. K.
Published: January 2005

An accurate adiabatic potential for the X 1Σg+ state of H2 calculated by Kol/os and Wolniewicz has been used in direct numerical solutions for the radial Schrödinger equation. The bond dissociation energy lies at the lower bound of the present experimental uncertainty, namely 36112.7 cm−1. Vibrational and rotational term value separations are in excellent agreement with experiment, especially for low v and J states. Expectation values for 〈r−2〉 are also in very good accord with observed rotational constants. Hence, a primary conclusion of this work is that the adiabatic approximation gives a highly accurate representation of the ground state of molecular hydrogen. Also, the procedure used here affords a convenient means of generating accurate radial wavefunctions for a variety of practical purposes. Additional topics treated are the comparison of this approach with the nonadiabatic calculation of Kol/os and Wolniewicz, and the extent to which an analysis of the H2 data can be made in terms of the traditional approach used in diatomic spectroscopy of two-point masses rotating and vibrating under the influence of a potential which is a single-valued function of the internuclear distance. Specific results obtained are a reduction in the uncertainty of the zero-point energy (with a slight adjustment in its most probable value) and a method for determining the force constant for this potential to five-figure accuracy. In the absence of experimental data, the Kol/os and Wolniewicz potential appears to provide a better extimate of the term values and rotational constants for tritium-containing isotopes of hydrogen than do isotopic relations applied to the ambiguous molecular constants for H2. Hence, a table of vibrational term values and rotational constants for the six hydrogen isotopic species is given as an appednix.
Optical and Paramagnetic Resonance Spectra of Some Trigonal Co(II) Chelates
Authors: Jesson J. P.
Published: January 2005

Paramagnetic resonance has been observed at 4.2°K in magnetically dilute single crystals and powders of bis[hydrotris(1-pyrazolyl)borate]Co(II) and bis[tris(1-pyrazolyl)methane]Co(II) chelate systems. The chelate structure for both types of compound has D3d symmetry, and the principal g tensor components show large axial anisotropy. In conjunction with optical data for these complexes, the results are analyzed in terms of the theory of Abragam and Pryce. In addition to the experimentally determined g values for the lowest Kramers doublet in these complexes, approximate g values and splittings are established for the other levels in the ground state manifold. Magnetically dilute powder measurements are described both for the compounds studied as single crystals and for a number of other cases where crystals could not be grown.
Theoretical Depolymerization Kinetics. III. The Effect of Molecular-Weight Distribution in Degrading Polymers Undergoing Random-Scission Initiation
Authors: Boyd Richard H. , Lin Tung-Po
Published: January 2005

Differential equations describing the rate of change of the moments of the molecular-weight distribution in the random-scission-initiated degradation of a heterodisperse polymer have been derived from the kinetic rate equations. These moment equations are used as the basis of an approximate treatment in which differential equations for the parameters in the Schulz—Zimm distribution are derived. These three equations have been solved by digital computer for a wide range of initial distributions and kinetic parameters. The effect of molecular-weight distribution on this type of degradation is discussed on the basis of the above equations.
Polymer Dynamics: Boson Representation and Excluded-Volume Forces
Authors: Fixman Marshall
Published: January 2005

The matrix formalism previously introduced for the discussion of polymer dynamics is rendered more tractable by the introduction of an explicit operator representation satisfying boson commutation rules. Techniques are devised by which singular functions of segment coordinates may be expanded in a fluctuation series (containing ordered products of boson operators) around an equilibrium or nonequilibrium average. The techniques are here applied to equilibrium excluded-volume expansions, and are shown to give good results. The detailed numerical results are presented in the following paper. The Gaussian potential is adopted for polymer chains in a theta solvent, but methods for its improvement are considered.
Accurate Potential-Energy Function for Diatomic Molecules
Authors: Levine Ira N.
Published: January 2005

A three-parameter potential-energy function for diatomic molecules proposed by Varshni and Shukla, has been modified to improve its accuracy. The modified function is U=De{1−(re/r)exp[−a(rp−rep)]}2, where De is the molecular dissociation energy, re is the equilibrium internuclear distance, and p=2+14(Δ12−4)(Δ12−2)/(Δ12−1), where Δ=½kere2/De, ke being the force constant. This function appears to be more accurate than previously proposed three-parameter functions.
Deuterium Isotope Effects on Molecular Dipole Moments by Microwave Spectroscopy
Authors: Muenter J. S. , Laurie V. W.
Published: January 2005

A special parallel-plate microwave spectrometer has been constructed and the effect of deuteration on the dipole moment in the ground vibrational state of seven different molecules has been measured. The molecules studied were: methylacetylene, propane, methyl fluoride, fluoroform, vinylidene fluoride, methylsilane, and methylgermane. With the exception of fluoroform, where an effect of 0.001 D was observed, the magnitude of the isotope effect was found to be of the order of 0.01 D. A simplified interpretation of the isotope effects leads to information about the signs of the dipole moments in these molecules.
Analysis of Carr—Purcell Spin-Echo NMR Experiments on Multiple-Spin Systems. II. The Effect of Chemical Exchange
Authors: Allerhand Adam , Thiele Everett
Published: January 2005

A general matrix formulation for the treatment of Carr—Purcell spin-echo (CPSE) nuclear magnetic resonance experiments on systems undergoing chemical exchange between r sites is presented. Indirect spin coupling is ignored. A simple similarity transformation is given, which makes the matrix L (a basic quantity in the theory) Hermitian, and clearly exposes its positive definite character. As a consequence, it is shown that the general solution for the complex transverse magnetization in the rotating frame is, at the nth echo, a sum of r terms of the form [A+(−1)nB]exp(−ntCPR), where tCP is the interval between 180° pulses, and R is a real positive function of tCP. A computer program calculates all these quantities. In many cases of interest, such as fast exchange, one exponential term dominates in this sum.

For fast exchange, a second-order perturbation treatment can be used to derive an explicit equation for the dominant decay time constant R1. This equation reduces to the Luz—Meiboom equation in the special case considered by those authors. The second-order treatment also gives an expression for the steady-state high-resolution linewidth. This equation reduces to the Piette—Anderson equation under the same special conditions for which the Luz—Meiboom equation holds. Detailed calculations which illustrate the use of the second-order equations are exhibited for the cases of the hydride shift in the 2-norbornyl cation and the degenerate Cope rearrangement in bullvalene.

The second-order equation takes a particularly simple form when applied to the study of a nucleus A coupled to a quadrupolar nucleus X. The result shows that one can extract both the magnitude of the coupling constant JAX and the relaxation time TX from the CPSE experiment on A, even when the high-resolution spectrum shows a single line.
Some Consequences of the Gibbs—DiMarzio Theory of the Glass Transition
Authors: Moacanin J. , Simha Robert
Published: January 2005

Using the Gibbs—DiMarzio theory of the glass transition, we have derived an expression for the Simha—Boyer parameter K1=(αL—αG)TG , which is a function only of the fractional unoccupied volume at T2, i.e., K1=—V0 lnV0. The analysis of the theory shows that T2 is proportional to the chain stiffness parameter ε, and is zero for a chain of zero stiffness. Wide variations in the intermolecular energy parameter E0 effect relatively minor changes in T2, and hence TG. But for values of ε smaller than E0 the theory predicts the absence of the discontinuity in the volume expansivities normally observed at TG. Furthermore the available experimental results indicate that ε and E0 may not be independent parameters, as originally defined.
Growth and Evaluation of High-Purity KCl Crystals
Authors: Butler C. T. , Russell J. R. , Quincy R. B. , LaValle D. E.
Published: January 2005

A method is described by which large, uniform KCl crystals of high purity can be obtained, starting with reagent-grade material. Chemical means are employed to produce pure polycrystalline ingots which are then used to grow single crystals by pulling from the melt under semiclean room conditions. The resulting crystals contain less than 1 μg/g of any foreign alkali or halide element, show OH concentrations of less than 40 μg/g and conductivity knees which indicate typically less than 300 parts per billion total polyvalent cation content. Analytical methods are discussed and analyses of these, as well as crystals from various commercial sources, are given.
On Certain Integrals Useful in Studies of Electronic Structure
Authors: Solony N. , Lin C. S. , Birss F. W.
Published: January 2005

Formulas are given for those two-center one-electron integrals, over Slater basis functions, of the type 〈χA|1/rAirB j|χB〉, 〈χB|1/rAirB j|χB〉, and one-center two-electron integrals 〈χχ′|1/r122|χ″χ″′〉, which arise in the application of the generalized variational method.
Theory of the Nuclear Resonance Spectrum of a Polar Liquid in an Alternating Electric Field
Authors: Macomber J. D. , Waugh J. S.
Published: January 2005

It is suggested that the small secular effects produced in the NMR spectrum of a polar liquid as a result of molecular alignment in an electric field may be detected most easily through the sidebands produced when the field has an ac component. A general modulation theory previously developed is applied to predict the locations and intensities of these sidebands as functions of the relevant molecular and experimental parameters for three forms of the alignment-modulated spin Hamiltonian: (1) anisotropic chemical shift, (2) quadrupole interaction, (3) anisotropic shift plus direct and indirect dipole—dipole coupling.
Momentum Autocorrelation Function for Systems with Finite Spatial Boundaries
Authors: Nossal Ralph
Published: January 2005

An exact analytical expression is obtained for the momentum autocorrelation function of a particle moving in a one-dimensional box and slowed by dynamical friction. Comparison is made with the results of Rahman's computer experiment for liquid argon.
Exactly Solvable Nonlinear Relaxation Processes. Systems of Coupled Harmonic Oscillators
Authors: Shuler Kurt E. , Weiss George H.
Published: January 2005

A class of nonlinear relaxation processes is discussed which involves the interaction of two finite systems characterized by special forms of the transition probabilities. For these particular sets of transition probabilities it is possible to reduce the initial set of coupled nonlinear kinetic equations to a set of linear equations with time-dependent coefficients which are amenable to exact analytical solutions. This reduction is effected through the use of summational invariants expressed in terms of the appropriate combinations of the moments of the distribution functions of the two systems. The vibrational—vibrational relaxation of two interacting systems of harmonic oscillators A and B with identical frequencies has been worked out as a specific example. For the type of relaxation processes discussed here it is found that the relaxation of System A is independent of the form of the initial distribution of System B (and thus of its time history) and vice versa.
Nuclear Magnetic Resonance of Nitrogen−14 in Potassium Azide
Authors: Forman Richard A.
Published: January 2005

The nuclear magnetic resonance of 14N split by large quadrupole interactions has been observed in single crystals of potassium azide (KN3). The observed spectrum at arbitrary orientation consists of eight resonance lines, which can be decomposed into two groups of four lines each. The resonances in each group are of the same apparent intensity, and one group is twice as intense as the other. The quadrupole coupling constants and asymmetry parameters of the two inequivalent nitrogens have been obtained from a rotation study. For the end nitrogen e2qQ/h=1.79±0.03 MHz with η=0.04±0.02. For the central nitrogen e2qQ/h=1.028±0.03 MHz with η=0.03±0.02. Unsuccessful attempts were also made to observe the pure quadrupole resonance of the end nitrogens.
Nuclear Magnetic Double Resonance of a Single Nucleus of Spin ½
Authors: Gordon Sidney L.
Published: January 2005

The nuclear magnetic double-resonance spectrum of a single nucleus of spin ½ is theoretically described by perturbation theory and by the Bloch equations. The perturbation theory correctly predicts all experimental features except line shapes and saturation effects. The description in terms of the Bloch equations provides a clear physical picture of the spin-½ problem. The analysis shows that the macroscopic moment is aligned with the effective field when the strong rf field is not in the immediate vicinity of the Larmor frequency. When the strong rf field is at the Larmor frequency, however, the macroscopic moment is perpendiclar to the effective field. This produces considerable changes in line shapes and intensities as the strong rf field approaches the Larmor frequency. The spectrum in this region is sensitive to the relaxation times, and provides a steady-state method for measurement of relatively short relaxation times. The theory is confirmed by frequency-sweep double-resonance experiments on chloroform saturated with oxygen.
Calculations on πunp Rydberg Terms of the Nitrogen Molecule
Authors: Duncan A. B. F. , Damiani Antonio
Published: January 2005

A more thorough calculation is made of the lowest terms in the Worley—Jenkins Rydberg series in molecular nitrogen. A complete variation of the energy is made with respect to the screening parameters in the Rydberg functions for n=3, 4 and limited variation with parameters for functions with n=5, 6, 7. In every case investigated, a stable minimum in the term energy was found. Terms with n=5, 6, 7 agree with experimental terms to about 10%, and differences appear to decrease slightly with increasing n.

Some variation was made in parameters of the core function and the effect of this limited variation on the Rydberg terms is discussed. A brief discussion is made of results on computed Rydberg defects.
Photoionization of High-Temperature Vapors. I. The Iodides of Sodium, Magnesium, and Thallium
Authors: Berkowitz J. , Chupka W. A.
Published: January 2005

A vacuum-ultraviolet monochromator, a mass spectrometer, and a molecular-beam source of high-temperature vapors have been combined to obtain photoionization efficiency curves of high-temperature species. In the TlI system, the ions Tl+, I−, and TlI+ were observed. Two independent threshold processes yield 2.770 and 2.769 eV for D0(TlI). The ions Na+, NaI+, Na2I+, Na2I2+, and Na3I2+ were detected in NaI vapor. The threshold for Na+ yields 3.00 eV for D0(NaI). No negative ions were observed in NaI vapor. The ions MgI2+ and MgI+ were measured in MgI2 vapor, the latter providing a basis for estimates of the energies for successive removal of I atoms from MgI2. The ionization potentials of TlI, NaI, Na2I2, and MgI2 are found to be 8.469, 7.64, 7.64, and 9.57 eV, respectively.
Hartree—Fock Parameters for the Atoms Helium to Radon
Authors: Froese Charlotte
Published: January 2005

Numerical Hartree—Fock calculations for ground-state or near-ground-state configurations have been performed for the neutral atoms helium to radon. Some typical results in the form of tables of atomic parameters are reported for La, Ce, Pr, and Nd.
Thermodynamics of the Lambda Transition in Liquid Sulfur
Authors: Klement William
Published: January 2005

The thermodynamics of the lambda transition in liquid sulfur is examined in terms of the Pippard relations. Using West's specific-heat results and critically evaluated thermal-expansion data, the initial slope of the λ line in p—T space, (∂p/∂T)λ, is estimated as ∼−42 bar deg−1. It is suggested that the ultrasonic measurements for liquid sulfur are inadequate, especially near the lambda transition, and that there is, hence, insufficient knowledge of the compressibilities. The present estimate for (∂p/∂T)λ compares favorably with that predicted from a theory of equilibrium polymerization and the two approaches are suggested to be complementary.
Pressure-Dependent Transmission Coefficients. Isomerization of a Restricted Rotor
Authors: Herbst Eric , Wilson David J.
Published: January 2005

Buff and Wilson's modification of Slater's ``new approach'' to unimolecular rate theory is used to calculate a pressure-dependent transmission coefficient for the isomerization of a restricted rotor. The calculation takes account of the possibility that a newly produced product ``molecule'' may back react before it is collisionally stabilized.
Phase Transitions in One Dimension and the Helix—Coil Transition in Polyamino Acids
Authors: Poland Douglas , Scheraga Harold A.
Published: January 2005

Phase transitions in one dimension are discussed from the point of view of order—disorder transitions in linear polymers using the formalism of sequence generating functions due to Lifson. If the statistical weight vj of an ordered sequence of j units has the form (lnvj)/j=a—bj−α, then a phase transition occurs when 0<α<1. As demonstrated by Fisher, this will occur, for example, if certain many-body interactions of short range are introduced. This behavior is obtained if we consider long-range pair potentials of the form 1/r1+α, for 0<α<1, occurring between all the units of an ordered sequence. An exponential potential, e−γx, gives a phase transition in the limit γ→0 if interactions are restricted to the units in an ordered sequence. The occurence of a phase transition arises from the convergence of the sequence generating function and its first derivative at the value of the unit partition function equal to the statistical weight of the ordered unit. This gives rise to a bend in the curve of the unit partition function as a function of temperature and, hence, a discontinuity in the population of ordered states. End effects in an ordered sequence in one dimension (the analog of surface effects in higher dimensions) are equivalent to the case of α=1; hence, as in polypeptides, one-dimensional systems with end effects show no true discontinuities.
Effect of Excluded Volume on Phase Transitions in Biopolymers
Authors: Fisher Michael E.
Published: January 2005

The effects of excluded volume on the existence and nature of a phase transition in an infinitely long double-stranded helical polymer are discussed in relation to the recent treatment of Poland and Scheraga, which showed that, if the entropy of a closed polymer loop of 2l links (corresponding to a diassociated length of l polymer units) varies as S2l/kB=al−clnl+b  (l→∞),then a genuine phase transition should occur if c>1 but that θ, the fraction of ordered units, would be continuous at the transition unless c>2. The standard Markoffian models of a polymer chain neglect the excluded volume and yield c=½d for a general d-dimensional system. Numerical data on self-avoiding lattice chains and rings are reviewed and it is concluded that c≃1.46 and 1.75 are better estimates for d=2 and 3, respectively.

The transition should thus remain continuous but it becomes sharper since it is shown that θ varies as (Tt—T)(2−c)/(c−1) when the transition temperature Tt is approached from below (and 1<c<2).
Excited Electronic States of Cyclopropane
Authors: Brown R. D. , Krishna V. G.
Published: January 2005

The cyclopropane molecule is treated as a system of delocalized σ electrons with respect to the carbon skeleton by a method similar to the Pariser—Parr treatment of π-electronic states. The results predict an A2′ state as the lowest singlet excited state and two 1E′ states above it. Experimental findings are seemingly in agreement with these calculations, corroborating the application of the delocalization model at least qualitatively. A triplet state of A2′ orbital symmetry is predicted to lie about 0.5 eV below the lowest 1A2′ state. If the configuration interaction is much larger than these calculations indicate, the lowest excited singlet state would be of E′ symmetry and the absorption now characterized as 1A1′→1A2′ could be due to the lowest singlet→triplet transition.
Viscoelasticity of Networks Consisting of Crosslinked or Entangled Macromolecules. I. Normal Modes and Mechanical Spectra
Authors: Chompff A. J. , Duiser J. A.
Published: January 2005

A molecular theory is developed to describe quantitatively the mechanical behavior of entanglement networks of linear, randomly coiling molecules. The theory is based on the model of Rouse for a single molecule and is a generalization of the theory of Duiser and Staverman for chemically crosslinked networks.

A new model for an ``entanglement point'' is suggested, which accounts for the frictional force due to the velocity difference between two entangled molecules at that point. This leads to a modification of the diffusion equation in the Rouse theory.

It turns out that the relaxation spectrum of a network corresponds to that of an assembly of ``decoupled'' equivalent molecules in which the ends of some submolecules have a mobility which is smaller by a slip factor δ. This parameter may have values from zero (crosslinked molecules) to unity (free molecules in dilute solution).

The relaxation spectra of the decoupled equivalent molecules can be obtained by applying a property of the Sturm sequence in a computer program, without actually solving for the eigenvalues of the modified matrix in the Rouse diffusion equation.

Application of the theory to experimental data yields the number of elastically effective network chains of an entanglement network by integration of the area under the curve in the long-time region of the relaxation spectrum.
Use of Numerical Integration in the Computation of the Expectation Value of H2 with Applications to H2
Authors: Goodisman Jerry , Secrest Don
Published: January 2005

The use of numerical integration for evaluating the expectation values of the Hamiltonian and the square of the Hamiltonian is difficult due to the presence of singularities in the integrand. A basis set is discussed which removes one of the principal singularities from Hψ in the case of the hydrogen molecule. This basis set is used and all integrals are evaluated numerically to obtain variational upper bounds and Weinstein and Temple lower bounds for the ground state of H2. First-excited-state upper bounds are obtained by a method involving the expectation value of the square of the Hamiltonian and the possibility of computing excited-state wavefunctions by minimization of the width, W=〈H2〉—〈H〉2, is discussed.
Triplet States of Liquid Benzene and Toluene
Authors: van Loben Sels James W. , Dubois Jean T.
Published: January 2005

The sensitization of biacetyl phosphorescence has been used to study the triplet states of benzene and toluene in the undiluted (neat) liquids. The results are not consistent with the expected triplet—triplet transfer and suggest that the transferring species is a form of the excimer. For benzene, this species is found to have a lifetime of 1±0.5×10−8 sec, whereas in toluene it is not detected. Upon dilution of the benzene by a factor of 7 with hexane, biacetyl phosphorescence sensitization is no longer detectable.
Mechanisms of Energy Transfer Involving Trivalent Tb and Sm
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

The sodium (yttrium, rare-earth) tungstates are particularly useful for the study of rare-earth (RE) ion interactions that lead to the enhancement or quenching of emission. On the average a given RE ion interacts with only six others by nearest-neighbor or next-nearest-neighbor exchange at maximum concentration. Therefore, quenching resulting from exchange coupling of ions of the fluorescent species of interest with such neighbors may be taken to vary with the fraction of dodecahedral sites occupied by RE ions (x) as [1—(1—x)6]. In general, interactions between cations that reduce intensity by a fraction that is less than [1—(1—x)6] probably involve exchange, while those that do so to a greater extent involve the cross relaxation of energy by multipolar transitions. Lifetime and intensity data obtained on sodium rare-earth tungstates containing trivalent terbium (Tb) and trivalent samarium (Sm) are examined herein. Energy transfers between Sm ions by a dipole—quadrupole mechanism and from Tb to Sm—Sm or Sm—Tb couples by a similar multipolar process. Transfer to single Sm ions by exchange enhances emission from Sm. However, this process is only competitive at low Sm concentrations.
Chemisorption of Nitric Oxide on Tungsten
Authors: Yates John T. , Madey Theodore E.
Published: January 2005

The chemisorption of NO on polycrystalline W has been investigated using a combination of ultrahigh-vacuum techniques: flash-desorption mass spectroscopy and field-emission microscopy. It has been found that NO chemisorbs nondissociatively on W at room temperature. Dissociation occurs at elevated temperature with an activation energy of about 47 kcal/mole (197 kJ/mole). Kinetic evidence indicates that dissociation involves the interaction of an adsorbed NO molecule with a neighbor empty site. At high NO coverage, dissociation is rate controlling for the liberation of ω-mode nitrogen near 1000°K. Heating of an NO-shadowed W field-emission tip above ∼700°K results in the formation of a receding boundary which remains sharp during the entire course of its backward motion over the initially covered region. This behavior is consistent with a model involving dissociation of NO at the boundary where empty sites are available. For monolayer NO (1.4×1015 molecules cm−2) on polycrystalline W, Δφ=+1.85±0.10 eV; this corresponds to an average surface dipole moment of 0.35-D per chemisorbed NO molecule at full coverage.
Semiclassical Theory of Spectra and Relaxation in Molecular Gases
Authors: Gordon R. G.
Published: January 2005

A theory is given for the rotational band contours in microwave, infrared, and Raman spectra, and for nuclear spin—lattice relaxation times. The results are a generalization of Baranger's impact calculation for atomic spectra. The semiclassical approach makes possible nonperturbative calculations beginning directly from the intermolecular potential. When the rotational lines are well resolved, the results reduce to our previous semiclassical expressions for the widths and shifts of isolated rotational lines. At higher densities the results describe the ``collapse'' or narrowing of the band contour which happens when the rotational lines overlap.
Abstraction of Hydrogen Atoms from Isobutane-d9 by Methylene
Authors: Halberstadt M. L. , McNesby J. R.
Published: January 2005

The photolysis of ketene at 3130 Å in the presence of isobutane-d9 was carried out at 320°C in order to determine the mechanism of methyl-radical formation. The two possibilities considered are: Mechanism I—insertion followed by internal relaxation and finally expulsion of a methyl radical, and Mechanism II—direct abstraction. Mechanism II was found to be the only detectable mode of methyl-radical formation. The effect of pressure on the isotopic methane distribution was studied and an attempt is made to explain the effect in terms of long-lived excited pentanes.
Vacuum-Ultraviolet Absorption Spectrum of Polyethylene
Authors: Partridge Roger H.
Published: January 2005

The absorption spectrum of polyethylene is reported from onset of absorption, at about 1780, to 1050 Å. The spectrum and probably also the solid-phase ionization potential, is shown to be similar to those of short chain n-alkanes in the vapor phase. No evidence is found of ``dissociative excitons'' or of an intramolecular band structure in polyethylene, while the probable ionization potential seems higher than suggested by some theoretical calculations.
Infrared Spectra of HCl and DCl in Solid Rare Gases. II. Polymers
Authors: Keyser L. F. , Robinson G. W.
Published: January 2005

Dimers and trimers of HCl, of DCl, and of mixed isotopic composition are identified from their infrared absorption spectra in rare-gas host matrices. One dimer and at least two different trimers have been found. The vibrational frequencies of these aggregates can be quantitatively explained on the basis of a model where: (1) the molecules are situated at substitutional sites in the close-packed rare-gas crystal; (2) nearest-neighbor intermolecular resonance interactions, identical in magnitude with those in the pure HCl or DCl crystal, act to split the states of the aggregate into components about a ``center of gravity''; (3) the position of the ``center of gravity'' depends upon the size but not the shape of the aggregate, decreasing in frequency toward the pure crystal limit as the aggregate grows. From an explanation of a portion of the trimer spectra, the sign of the intermolecular coupling constant was found to be positive. The relative intensities of the various spectral components are used to estimate the intermolecular orientations within the aggregate. While these estimates, which are based on an ``oriented gas model,'' should be viewed with caution, the data suggest that the relative nearest-neighbor orientation approaches that of the crystal as the polymer size increases. The orientation in the dimer is very different from that in the crystal while the orientation in the trimer is intermediate between these two extremes. There is no obvious relationship between the HCl dimer observed in the rare-gas matrix and that observed by Rank, Sitaram, Glickman, and Wiggins in the gas phase.
Fourier Transform Analysis of Hyperfine Structure in ESR
Authors: Silsbee Robert H.
Published: January 2005

A new approach is outlined for attacking the analysis of ESR spectra showing poorly resolved hyperfine structure due to several nuclear species. The theoretical synthesis of the Fourier transform of the expected spectrum for a specific model is simpler to perform than the synthesis of the spectrum itself. Hence useful information and clues to the nature of a correct model may be obtained by considering the transform of the spectrum as well as the direct spectrum. The method is developed and an example of such a synthesis is discussed.
Correlation of Electronic Structure and Bending Force Constants in Some Linear Molecules
Authors: Smith Wm. Hayden , Leroi George E.
Published: January 2005

A qualitative relationship between electron density in the outermost occupied orbital at the central carbon atom and ease of bending is described for several triatomic and pentatomic linear molecules, including CO2, C3, NCN, C3N2, C3O2, C3S2, and C3H4. Both valence bond and molecular orbital models are discussed.
Studies of Hydrogen-Bonded Systems. IV. Radiation-Induced Tunneling and Tautomeric Equilibria in the Guanine—Cytosine Base Pair
Authors: Rein Robert , Harris Frank E.
Published: January 2005

Electronic energies are calculated for the ground states of the cation and anion of the guanine—cytosine base pair, using an approximate self-consistent-field method described earlier by the authors. The calculations are made for a series of positions of the hydrogen-bonded protons, all three of which are explicitly included in the formulation. The results are used to discuss equilibria and proton tunneling between tautomeric forms, and an indication is given of the possible connection between these phenomena and radiation-induced mutation.
Pseudonatural Orbitals as a Basis for the Superposition of Configurations. I. He2+
Authors: Edmiston C. , Krauss M.
Published: January 2005

The use of pseudonatural orbitals (PNO) is proposed to improve the rate of convergence in the superposition of configurations (SOC). Natural orbitals are determined for selected electron pairs in the Hartree—Fock field of the n−2 electron core and are then used as the basis for the total SOC calculation. Since these natural orbitals are not natural for the n-electron system they are considered false or pseudonatural orbitals when used in the n-electron problem.

The PNO basis has been applied to He2+ and H3 to test the convergence. Complete results are reported here only for He2+. The PNO's are quite successful in speeding up the convergence of the SOC and rendering the calculation of correlation energy quite practical in general. Gaussian-type orbitals (GTO) are used throughout and were not a serious impediment to obtaining quantitative accuracy. In fact the large number of unoccupied Hartree—Fock orbitals consequent upon the use of a GTO basis permit a straightforward determination of the PNO orbitals.
Relationship Between Pair Potentials and Distribution Functions
Authors: Strong S. L. , Kaplow Roy
Published: January 2005

It is demonstrated that the relationship between pair potentials and distribution functions is experimentally ambiguous for dense fluids. Calculations in the Percus—Yevic approximation show that qualitatively different potentials can be chosen which predict pair distributions which are virtually indistinguishable, and vice versa.

In addition, if the nearest-neighbor interaction is predominant, it appears that the assumption of symmetric interactions may not be valid in liquids such as mercury and tin.
Thermodynamic Relations between Anomalous Quantities near a Lambda Transition in Anisotropic Dielectrics
Authors: Janovec V.
Published: January 2005

The thermodynamic treatment of the λ transition in liquid helium developed by Buchingham and Fairbank is generalized for transitions in anisotropic dielectrics. Tensor relations between the heat capcity cσ,E, the elastic compliances sμνT,E, the thermal expansion coefficients αμσ,E, the pyroelectric coefficients piσ,E and the piezoelectric coefficients diμT,E are derived, and a connection established between the symmetry and the coupling of anomalous quantities. It is shown that the asymptotic forms of the general equations lead to the Pippard—Garland equations with specified electric boundary conditions and, in addition, to a new set of equations that relate pyroelectric and piezoelectric coefficients in the transition region. Experimental data for triglycine sulfate near the ferroelectric phase transition are analyzed, and it is shown that the anomalous quantities cσ,E, sμνE, αμσ, and piσ,E, diμE are linearly related within the temperature interval (Tc—T) <16°, where the constants of proportionality give the numerical values of the components of a tensor describing the change of Tc due to mechanical stresses.