bluuebunny/crossref_metadata_2025_split huggingface dataset:
United-Atom Approximation Applied to Argonlike Molecules. I. Hydrogen Sulfide
Authors: Banyard K. E. , Hake R. B. 
Published: January 2005

The united-atom approximation was applied to H2S and also to the systems HS— and S——. The wavefunction obtained for H2S was used to calculate the molar diamagnetic susceptibility and the coherent x-ray scattering factor for the gaseous form of the molecule. Values are also reported for the ``breathing'' force constant for H2S and for the theoretical bond length for both H2S and HS—.
Within the present approximation a calculation was made of the bond energy for H2S dissociating into HS and S. The proton affinities for HS— and S—— were also determined.
Where possible, a comparison was made with experiment. In general, except for the proton affinities and bond-energy calculation, the united-atom model applied to H2S was reasonably successful. A comparison was also made between the present radial density and the density of electrons for H2S provided by the model of ``floating'' hydrogen densities. This comparison helps to substantiate the claim made earlier, namely, that the model of ``floating'' hydrogen densities will provide a very reasonable radial distribution of electrons within molecules of the form XHn.
Heat of Formation of Be2O(g) by Mass Spectrometry
Authors: Theard Lowell P. , Hildenbrand Donald L. 
Published: January 2005

Mass spectrometric Knudsen effusion experiments have provided evidence for the existence of the suboxide species Be2O(g) in the equilibrium vapor above crystalline beryllium oxide at temperatures around 2300°K. Be2O+ ions appear to be formed both by simple ionization of Be2O(g) and by fragmentation of a larger molecule. The relative importance of the two processes has been shown to be temperature dependent. An average value of —8±10 kcal/mole was obtained for ΔHf°298[Be2O(g)] from third-law calculations for three equilibria.
Mass spectral data are given for the equilibrium vapor above beryllium oxide at 2380°K in the presence of tungsten.
Molecular Structure of CF3PCl4: Infrared and Raman Spectra
Authors: Griffiths James E. 
Published: January 2005

The basic structure of the CF3PCl4 molecule has been established from a study of its vibrational spectrum. The CF3 group occupies an axial position in the trigonal bipyramidal structure but no information is obtained concerning the height of the barrier to internal rotation.
All of the active fundamentals are assigned in the Raman spectrum (Δv=50–1500 cm—1) and supplementary data were obtained from a pressure limited gas-phase study of the infrared spectrum (2000–280 cm—1). Fundamental frequencies are: a1=1145, 743, 493, 374, 324, 260; e=1168, 587, 543, 304, 239, 193, and 94 cm—1.
The compound is unstable thermally decomposing into CF3Cl, CF3PCl2, PCl3, and PCl5.
Automatic Calculation of the Transport Collision Integrals with Tables for the Morse Potential
Authors: Smith Francis J. , Munn R. J. 
Published: January 2005

A computer program is described for calculating the classical and quantal JWKB Chapman—Enskog collision integrals Ω(l,s) (T) for any reasonable interaction potential. With the program it was possible in about 10 or 15 min on a fast computer to calculate more than 500 collision integrals covering a complete range of values of l, s, and T to an accuracy of better than 1 part in 1000. This was made possible by the use of efficient numerical techniques such as weighted Gaussian quadratures and by the general optimization of all numerical and logical processes.
The program was checked against previous tables for the Lennard-Jones and Stockmayer potentials. It was also used to list values of the collision integrals and Kihara's corrections to the coefficients of viscosity, thermal conductivity, diffusion and thermal diffusion for the Morse potential.
Knight Shifts and Relaxation Times of Alkali-Metal and Nitrogen Nuclei in Metal—Ammonia Solutions
Authors: O'Reilly D. E. 
Published: January 2005

Knight shifts of 7Li, 23Na, 87Rb, 133Cs, and 14N in alkali-metal—ammonia solutions have been measured at 300°K and in the concentration range 0.03 to 1 mole liter—1. 23Na NMR has been observed at Na concentrations down to 0.003 mole liter—1 at 300°K and in the range 0.03 to 4 mole liter—1 at 274° and 240°K. 14N shifts are reported for concentrations from 0.008 to 4 mole liter—1 at 300° and 240°K. Linewidths of 87Rb and 133Cs have been obtained at 300°K in the concentration range 0.03 to 0.8 mole liter—1. At 0.35 mole liter—1 and 300°K the shifts of Li, Na, Rb, and Cs are 9, 72, 450, and 900 ppm, respectively, to lower magnetic field. Shifts of 14N are nearly independent of metal at 300°K.
The concentration and temperature dependence of 23Na Knight shift data at concentrations up to 0.4 mole liter—1 may be quantitatively interpreted by the following reactions: M⇌M++e−,M+e−⇌M−,where M represents the ``monomer'' species and (2) is the spin-pairing reaction. The 14N spin density at unpaired electron is essentially independent of alkali metal and concentration up to 0.6 mole liter—1 and equal to 0.88±0.11 a0—3 at 300°K. The electron spin density at 23Na is calculated to be ≥8×10—3 a0—3 approximately independent of temperature and concentration.
The lifetimes of the Rb and Cs monomers at 300°K and 0.06 mole liter—1 are ≤3 and ≤4 μμsec, respectively, as determined from NMR linewidth measurements. The monomer lifetime decreases sharply with increase in metal concentration.
One-Electron Perturbations in Self-Consistent Field Theory
Authors: Wyatt Robert E. , Parr Robert G. 
Published: January 2005

Self-consistent field equations perturbed by one-electron operators are examined, with the aim of justifying the use of uncoupled equations at the first-order level. The independent-orbital equations of Sternheimer for the first-order corrections are shown to differ from the exact first-order SCF equations by sums of pair-coupling functions Aij which bring perturbed orbital j into the differential equation determining the perturbed orbital i. It is shown that the off-diagonal Lagrangian multipliers εij0 and εij(1) that appear in the unperturbed and perturbed SCF equations can be chosen so that ∫ φi0Aijdv= ∫ φj0Ajidv=0and ∫ (Aij2+Aji2) dv=minimum,where the φi0 are the unperturbed SCF orbitals. Complete neglect of the functions Aij—the Sternheimer method—is thereby given a firm basis. Further analysis provides a perturbation—iteration method for determining residual coupling effects.
An alternative analysis also is presented in which the Sternheimer equations are obtained directly from the perturbed SCF equations by treatment of the exchange operator, the change of the Coulomb-exchange operator, and the operator generating the off-diagonal εij as pseudoperturbations that act cojointly with the pure-field operator. Integrodifferential equations are given for both the pure-field corrections and the corrections evolved by the pseudoperturbations.
Separation of Sets of Variables in Quantum Mechanics
Authors: Marcus R. A. 
Published: January 2005

Separation of the Schrödinger equation for molecular dynamics into sets of variables can sometimes be performed when separation into individual variables is neither possible nor for certain purposes necesary. Sufficient conditions for such a separation are derived. They are the same as those found by Stäckel for the corresponding Hamilton—Jacobi problem, with an additional one which is the analog of the Robertson condition for one-dimensional sets.
Expressions are also derived for operators whose eigenvalues are the separation constants. They provide a variational property for these constants. For use in aperiodic problems an expression is obtained for the probability current in curvilinear coordinates in an invariant form. Application of these results to reaction rate theory is made elsewhere.
Local Approximation of Potential-Energy Surfaces by Surfaces Permitting Separation of Variables
Authors: Marcus R. A. 
Published: January 2005

In the immediate vicinity of a potential-energy minimum or of a saddle point, it is shown that major topographical features of a ``nonseparable'' potential-energy surface can be imitated by those of a surface permitting separation of variables. For each extremal path of descent or ascent to the cited critical point of the surface, there is an exact match of the tangent, the first curvature vector in configuration space, and the force constant along that path provided that the known curvature vector satisfies an equation containing the metric tensor of the selected coordinate system and known force constants. Because of the wide choice of coordinate systems available for selection, it is anticipated that this relation may be fulfilled for each extremal path, partly by choice of the coordinate system and partly by subsequent choice of the curvilinear coordinates of the critical point.
There are several possible applications of this local approximation, including those to problems involving anharmonic coupling of normal modes and those involving n-dimensional tunneling and other calculations in reaction-rate theory. Use will be made of the formalism to extend the activated complex theory in chemical kinetics. As a preliminary test of the local-approximation concept, literature data on n- and one-dimensional tunneling rates are compared. They are found to be fairly similar when proper cognizance is taken of zero-point energies.
Experimental Evidence for Localized Excitons in the Spectra of Charge-Transfer Complex Molecular Crystals
Authors: Hochstrasser Robin M. , Lower S. K. , Reid C. 
Published: January 2005

The polarized absorption and emission of the anthracene—TNB complex crystal are shown to provide evidence for localization of low-energy excitation in this crystal. The absorption and fluorescence polarization ratios at 300°K are very different (5.6:1 and about 15:1, ‖c: ⊥c on 110) the former being close to an oriented gas value. The latter corresponds to a charge-transfer complex more closely aligned with the c axis of the crystal. The motion of the excited molecule is in accord with the behavior of a dipole in an electric field which is nearly along the c axis. Possible ramifications of this effect in photoconductive charge-transfer complexes are discussed.
The influence of temperature on the luminescence spectrum of anthracene—TNB crystals is discussed, and apart from some artifacts due to cracking of crystals, the expected increase of emission intensity with decreasing temperature is observed.
Elastic and Reactive Scattering of K by HCl and HI in Crossed Molecular Beams
Authors: Ackerman M. , Greene E. F. , Moursund A. L. , Ross J. 
Published: January 2005

The elastic and reactive scattering of K by HCl and HI has been measured at several relative energies in experiments with crossed molecular beams. The interpretation follows that presented previously for K+HBr, with some improvements. For both systems the measurements on K show rainbow scattering, and from it parameters have been calculated for the exp-six potential. From the elastic scattering at large angles and a two-body model for it, the probability of reaction is deduced as a function of the potential energy at the distance of closest approach of the reactants.
For K+HCl the potential parameters are ε=0.45±0.02 kcal/mole and rm=3.2±0.3 Å for α=12 (assumed). The activation energy is 0.55±0.1 kcal/mole, as determined from the threshold of the probability of reaction, and is probably just the change in zero-point energy for this endothermic reaction. There are indications that the probability of reaction increases when the potential energy is sufficient for the product KCl to be formed in excited vibrational states. The application of the two-body model at the thresholds of formation of KCl allows another determination of rm which is in good agreement with the value obtained from the rainbow scattering. The total reaction cross section as obtained from the probability of reaction is 3.9 Å2 at Ē=2 kcal/mole. No measurements could be made on KCl.
For K+HI the potential parameters are ε=0.67±0.02 kcal/mole and rm=4.2±0.2 Å for α=12 (assumed). The activation energy of this exothermic reaction is 0.2±0.1 kcal/mole as determined from the threshold of the probability of reaction. The total reaction cross section as a function of relative energy has been obtained from measurements on KI and from the probability of reaction deduced from the elastic scattering. These two measures of the amount of KI produced agree within a factor of 2, which is the reproducibility of the measurements on KI. At a relative energy of 2 kcal/mole the total reaction cross section is 28 Å2.
Effect of Electrical Fields in the Gamma Radiolysis of Propane
Authors: Ausloos P. , Gorden R. 
Published: January 2005

The γ-ray radiolysis of C3H8–C3D8 mixtures and of CD3CH2CD3 has been investigated as a function of applied electrical field up to voltages necessary to cause secondary ionization. In the saturation current region, those products which in previous studies were ascribed to ethyl and vinyl ions remain constant with a change in field strength, while products which were originally attributed to the decomposition of neutral excited propane molecules are seen to increase about fivefold before the onset of secondary ionization. The inferred yields of C2H5+ and C2H3+ per ion pair at a propane pressure of 3 cm are 0.40 and 0.08, respectively. These values compare favorably with those deduced from the fragmentation of propane within 10—10 sec as calculated by Vestal, Wahrhaftig, and Johnston on the basis of the quasiequilibrium theory of mass spectra.
The modes of decomposition of the neutral excited propane molecules formed by electron impact are the same as those observed in the vacuum-ultraviolet photolysis at 1470 and 1237 Å. From the isotopic analysis of the products formed in the radiolysis of CD3CH2CD3 at high field strengths, it can be concluded that the average energy imparted to the neutral propane molecule by electron impact is larger than 10 eV, indicating that superexcited states of propane may be produced in the radiolysis. A value of 0.3±0.1 can be ascribed to the ratio of the number of neutral excited molecule decompositions to the number of ion pairs produced in the direct radiolysis of propane in the absence of an electrical field.
Molecular Schrödinger Equation. IV. Results for One- and Two-Electron Systems
Authors: Conroy Harold 
Published: January 2005

A general form, based upon configuration interactions, but including correlation to hasten convergence, is proposed for two-electron wavefunctions. The advantages of the correlation treatment developed include the ability to remove the singularity in the interelectronic potential from the Schrödinger equation. The results of sample calculations for hydride ion and helium are presented.
In addition, the results obtained in the application of our one- and two-electron treatments to the systems HeH++, HeH+, and linear and triangular H3++ and H3+ are discussed in detail, the accurate potential energy surfaces for the latter molecules having been elucidated.
Deuteron Magnetic Resonance Study of Some Crystals Containing an O—D···O Bond
Authors: Chiba Takehiko 
Published: January 2005

A deuteron magnetic resonance study was made on four compounds with an O—D···O hydrogen bond of different strengths. The deuteron quadrupole coupling constant eqQ, asymmetry parameter η, and the directions of the field gradient tensor were determined. The eqQ and η obtained are: KDCO3154.4±0.6 kc/sec,0.194±0.018,(COOD)22D2OD1(water)230.3±2.0 kc/sec,0.062±0.006,D2(water)219.1±2.0 kc/sec,0.16±0.03,}    (at−70∘C)   D1 and D2121±3 kc/sec,0.93±0.02,(at 67∘C)   D3(carboxyl)139.2±0.8 kc/sec,0.098±0.005,ND4D2PO4 (acid D)119.6±0.8 kc/sec,0.053±0.008,K, D−maleate 56.0±0.8 kc/sec,0.53±0.07.
The results are discussed in relation to the crystal structure in each case. It was found that the oxalic acid dihydrate crystal used was a new modification, different from the ordinary one. Reorientational motion of a water molecule similar to that in other hydrated crystals was observed in oxalic acid dihydrate from the measurement at different temperatures. A barrier to this motion of 10.0 kcal/mole was determined from the temperature dependence of the linewidth.
In each compound studied, correlation between the principal axis directions of the field-gradient tensor and the local atomic arrangement in the crystal can be readily observed. The direction of the largest principal component of the field gradient tensor is in good agreement with the O—D direction or the O—D···O direction. The direction of the second principal component is generally in good agreement with the normal to the plane defined by[Complex chemical formula]The deviation from the latter rule can be seen in D1 of oxalic acid dihydrate where O—D···O differs greatly from a straight bond.
A marked decrease of eqQ with increasing hydrogen-bond strength is observed. Both the field gradient and the square of the OH stretching frequency as a function of O···O distance are in fairly good agreement with each other, similar to the near equality of the field gradient and force constant in diatomic hydrides. The change in the electronic contribution to the field gradient with O–H distance in the hydrogen bonded system is estimated.
Relative Rates of Reaction of Bromine Atoms with Isotopic Hydrogen Molecules
Authors: Timmons Richard B. , Weston Ralph E. 
Published: January 2005

Kinetic isotope effects in the reaction of bromine atoms with isotopic hydrogen molecules were measured in this investigation. Rate constant ratios were determined by isotopic analysis of H2–HD, H2–HT, or H2—D2 mixtures before and after reaction with bromine atoms. Over the temperature range of 438° to 623°K, the ratios of the second-order rate constants were kH2/ΣkHD = (1.14±0.01) exp(591±4/RT), kH2/ΣkHT = (1.22±0.02) exp(658±16/RT), kH2/kD2 = (1.32±0.04) exp(1253±37/RT).
A comparison of these results with the corresponding isotope effects obtained in the chlorine- and iodine-atom experiments reveals surprisingly little difference in kinetic isotope effects.
The theoretical calculation of the kinetic isotope effects was carried out using Bigeleisen's theory of isotope effects on reaction rates. The calculations were made using various methods of constructing the potential energy surface and it was found that none of the semiempirical methods used gave agreement to better than 40% to 80%.
Nuclear Magnetic Resonance and Optical Spectroscopy of [Co(MeOH)5Cl]+ in Methanol and the Kinetics of Methanol Exchange of the Solvation Shell
Authors: Luz Z. 
Published: January 2005

A study of the complex formation of Co+ + ions with Cl— ions in methanol at temperatures between —60° and —80°C is reported. The tools used are nuclear magnetic resonance and optical spectroscopy. It is shown that at these low temperatures the dominant cobalt—chlorine complex is an octahedral monochloro complex, [Co(MeOH)5Cl]+. The NMR spectra give the following values for the hyperfine interaction constants between methanol protons and Co+ +: 0.49, 0.33, and 2.4 Mc/sec for, respectively, the methyl protons of methanol cis to the chlorine, the methyl protons of methanol trans to the chlorine, and the hydroxyl proton in methanol cis to the chlorine. At temperatures above —75°C exchange of methanol between the coordination sphere and the bulk solvent contributes to the width of the NMR peaks. The results suggest that the dominant exchange process follows an SN1 mechanism, involving the dissociation of a cis methanol molecule in the complex as the rate-determining step. The rate constant of this process is found to be 510 sec—1 at —63°C, and the activation energy 14.5 kcal/mole.
Optical absorption spectra of the monochloro complex in the visible range are reported. The spectrum of this complex is similar to that of [Co(MeOH)6]+ +, but the maximum absorption is slightly shifted to longer wavelength (from 507 to 527 mμ at —80°C), and the extinction coefficient is 2.7 times that of [Co(MeOH)6]+ +.
NMR Spectra of ClF3 and ClF: Gaseous Spectra and Gas-to-Liquid Shifts
Authors: Alexakos Louis G. , Cornwell C. D. 
Published: January 2005

Gas-phase 19F NMR spectra at 56.4 Mc/sec are presented for ClF3 over a range of partial pressures (300–1300 mm) extending to sufficiently low values that the shielding and spin—spin coupling constants found can be regarded as true molecular quantities. These are, for the AB2-type spectrum, (σA−σB)/(1−σB)=125.88×10−6,  |J|=441±8 cps.Small systematic relaxation effects in the multiplet splittings were identified and eliminated by graphical procedures.
NMR data are also given for ClF3 as a liquid and as a solute in CCl4 and CCl3F. While these spectra are similar enough to that of the gas to indicate that the T structure persists in all these phases, there are clear trends in σB and J for the sequence: gas, liquid solutions, pure liquid. These trends may result from the existence in the condensed phases of local structure similar to that found in the crystal.
Other chemical shifts (σ—σr) / (1—σr) measured for gases at low densities relative to SiF4(g) at 27°C are, in parts per million: ClF, 273.73; BF3, —36.11; CF4, —104.19; CCl3F, —167.60; ClF3(A), —187.32; ClF3(B), —313.24; ClO2F(?), —499.87; all with an experimental uncertainty of about ±0.10.
Kinetic Theory Analysis of the Reaction of Hot Hydrogen Atoms with Propane, Butane, and Butene-1
Authors: Rosenberg Allan H. , Wolfgang Richard 
Published: January 2005

The kinetic theory of hot reaction has been applied to results on the reaction of hot hydrogen atoms with propane, with butane, and with butene-1. Recoil tritium, generated by the 3He(n, p)T process served as the source of hot hydrogen. Yields of hot abstraction, displacement, and addition processes were measured by radio gas chromatography. Scavengers were used to suppress interfering thermal processes. Runs were made covering a wide range of moderation of the hot hydrogen by helium.
A complete analysis of the data and the use of appropriate internal consistency checks, shows that within experimental error the kinetic theory provides a satisfactory description of the system. Its application serves to express the data in terms of ``reactivity integrals'', I, and collisional energy loss parameters α. In accordance with previous expectations, the magnitudes of these quantities indicate that hot atom collisions are highly inelastic and have a high probability of leading to reaction.
Pulse Radiolysis Studies. VI. The Lifetimes of Aromatic Anions in the Aliphatic Alcohols
Authors: Arai Shigeyoshi , Dorfman Leon M. 
Published: January 2005

The formation and the lifetimes of several aromatic anions in irradiated solutions of arenes in the aliphatic alcohols have been investigated by the pulse radiolysis technique. The aromatic anions show a fast decay which follows a first-order rate law. The absolute rate constants for this decay, suggested to be a proton transfer from the alcohol, arene−+ROH=arene H·+RO−,have been determined for four alcohols and three aromatic anions. The rate constants, which are found to be in the order CH3OH&gt;C2H5OH≅C3H7OH&gt;(CH3)2CHOH, show a close correlation with other measurements of the acidity of the alcohols.
The absolute rate constants have also been determined for the reaction of several aromatic anions with hydrogen ion, arene−+ROH2+=arene H·+ROH,and for the attachment reaction of the solvated electron in ethanol, esol−+arene=arene−.