JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

15 Dec 1964

Volume 41, Issue 12, pp. 3663-4014

Page 1 of 3 Pages Next Page | Jump to Page

Accurate Adiabatic Treatment of the Ground State of the Hydrogen Molecule

W. Kołos and L. Wolniewicz

J. Chem. Phys. 41, 3663 (1964); http://dx.doi.org/10.1063/1.1725796 (11 pages) | Cited 408 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Accurate ground‐state energies of the hydrogen molecule have been computed using wavefunctions in the form of expansions in elliptic coordinates and including explicitly the interelectronic distance. The computations have been made with 54‐term expansions (0.4≤R≤3.7) and with 80‐term expansions (0.5≤R≤2.0). For the equilibrium internuclear distance, the best total energies obtained in the two cases are —1.1744701 a.u. and —1.1744746 a.u., respectively, the corresponding binding energies being 38 291.8 and 38 292.7 cm—1. Employing the 54‐term wavefunctions, the relativistic corrections and the diagonal corrections for nuclear motion have been computed for several internuclear distances. For equilibrium their contributions to the binding energy have been found to be —0.526 and 4.947 cm—1, respectively. Thus the final theoretical binding energy for H2 amounts to 38 297.1 cm—1 and is a little larger than the experimental value 38 292.9±0.5 cm—1. The discrepancy may be due to the adiabatic approximation.

Accurate Computation of Vibronic Energies and of Some Expectation Values for H2, D2, and T2

W. Kołos and L. Wolniewicz

J. Chem. Phys. 41, 3674 (1964); http://dx.doi.org/10.1063/1.1725797 (5 pages) | Cited 82 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The complete four‐particle nonrelativistic Hamiltonian and 147‐term wavefunctions have been used to compute the energies and the expectation values of several other operators for vibronic ground states and for the first vibrationally excited states of H2, D2, and T2. For H2 and D2 the computed dissociation energies, with relativistic corrections, are by 0.6 and 1.3 cm—1, respectively, larger than the experimental values.

Isothermal Diffusion in Systems with Glasslike Transitions

H. L. Frisch

J. Chem. Phys. 41, 3679 (1964); http://dx.doi.org/10.1063/1.1725798 (5 pages) | Cited 29 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Following Simon, we define fluid systems with a ``glasslike'' transition as systems which above the transition temperature Tξ are, and below Tξ are not in internal chemical equilibrium with respect to a set of unspecified internal parameters of even tensorial rank. We present the flow equations for the chemical components of such systems in various frames of references. In particular, in a mass‐fixed frame of reference, besides a variation in the Onsager coefficients, the flow equations below Tξ are subject to a different set of subsidiary conditions (the ``new'' Gibbs—Duhem equations). We also investigate the consequences of the assumption of sorption equilibrium at the surface of our diffusion system. We find that below Tξ these systems will possess history‐dependent diffusion coefficients and be subject to time‐dependent surface concentrations. We can relate these time dependencies to the relaxation of the internal parameters of the system below Tξ.

Studies on Absorption Spectra of Ni++ Ion in NiCl2 in Different Organic Solvents

N. S. Chhonkar

J. Chem. Phys. 41, 3683 (1964); http://dx.doi.org/10.1063/1.1725799 (6 pages) | Cited 2 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The absorption spectra of Ni++ ion in NiCl2 in six different organic solvents were studied with a Hilger Uvispek spectrophotometer from 10 000 to 3900 Å. A comparison between the calculated and observed values of oscillator strength strengthens our view that electric dipole transition coupled with vibration give rise to these bands.
From the lowering of the term separation the covalency factor is found to vary between 0.85 and 0.89 for the different solvents. The deduced g‐ and magnetic moment have almost the same value in all the solvents.
The cubic field coefficient in some solvents is found to be smaller than that in aqueous solution. The cluster about the Ni++ ion appears to be more anisotropic than in aqueous solution.

On the Kinetic Theory of Dense Fluids. XVIII. The Bulk Viscosity

Peter Gray and Stuart A. Rice

J. Chem. Phys. 41, 3689 (1964); http://dx.doi.org/10.1063/1.1725800 (6 pages) | Cited 22 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
A formula for the bulk viscosity of a simple liquid has been obtained from the solutions of the kinetic equations proposed by Rice and Allnatt. The reliability of numerical results obtained is limited to about ±20% by uncertainties in the radial distribution function, its density dependence, and the pair potential. Nevertheless, the theory unambiguously predicts that the ratio of bulk to shear viscosity for liquid argon, at a density of 1.12 g⋅cm—3 and temperatures between 128° and 185°K, should be approximately 1.3.

On the Kinetic‐Energy Distribution of Fragment Ions Produced by Electron Impact in a Mass Spectrometer

H. E. Stanton and J. E. Monahan

J. Chem. Phys. 41, 3694 (1964); http://dx.doi.org/10.1063/1.1725801 (9 pages) | Cited 24 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Distributions of initial kinetic energies have been measured for fragment ions that are produced in the breakup of the excited ions CO+, H2O+, NH3+, CH4+, and C6H6+. These ions were formed by electron impact. The energy of the ionizing electron beam was 400 eV in the case of benzene and 200 eV for the other target gases. The initial‐energy distributions of the fragment ions from H2O and CH4 were measured as a function of electron energy over the interval from 100 to 400 eV. No measurable change in the distributions was observed. Evidence presented indicates that the excess‐energy ion pair (masses 15 and 63) are formed simultaneously in the decay of doubly charged benzene ions. Included also in this paper are the details of an analytical method to correct measured energy distributions for kinematic effects and instrumental distortions. In this analysis the distributions of the internal energy converted into kinetic energy of the fragments are characterized by their moments.

Collisional Deactivation of the Excited Singlet Oxygen Atoms and Their Insertion into the CH Bonds of Propane

Hideo Yamazaki and R. J. Cvetanović

J. Chem. Phys. 41, 3703 (1964); http://dx.doi.org/10.1063/1.1725802 (8 pages) | Cited 68 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Reaction of the excited singlet oxygen atoms with propane was studied at room temperature and at pressures from 400 to 6400 mm. Three main processes were observed: (1) insertion of the excited singlet atoms into CH bonds, (2) abstraction of hydrogen atoms, and (3) fragmentation of the paraffin. The yields of the insertion products increased approximately linearly with the pressure, the abstraction products remained almost constant and the fragmentation products decreased. The primary step is the insertion of the excited singlet oxygen atoms into the CH bonds of propane to form ``hot'' alcohol molecules. When gases capable of deactivating the excited atoms are added, the insertion and fragmentation decrease and the secondary hydrogen atoms are preferentially abstracted. From the increased discrimination in hydrogen abstraction the following relative rates (k2/k3) of the electronic deactivation of the excited singlet oxygen atoms by different gases have been obtained: Xe 0.47, N2 0.15, Kr 0.05, and He and SF6 close to zero.

Perturbed Hartree—Fock Calculations. IV. Second‐Order Properties of the Fluorine Molecule

Richard M. Stevens and William N. Lipscomb

J. Chem. Phys. 41, 3710 (1964); http://dx.doi.org/10.1063/1.1725803 (7 pages) | Cited 43 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The coupled Hartree—Fock method with a limited basis set has yielded values at the F nucleus and at the center of charge C of the F2 molecule for the electric polarizability (α∥=2.15 Å3, α⊥=0.77 Å3), the magnetic susceptibility (extrapolated to —10.2 ppm), the magnetic shielding [σ=—276 at F or —200 at C (preferred value); σexpt1=—210 ppm], rotational magnetic moment (extrapolated to —0.108 nuclear magnetons) and spin rotation constant [CF=169 at F or 152 at C (preferred value); Cexpt1=157±2 kc/sec]. The poor gauge dependence for the shielding and spin rotation constant is associated with the unusually high paramagnetic shielding at F which is due specifically to an interaction of the occupied πu orbital with a low‐lying excited σu state. The susceptibility and rotational magnetic moment did not vary extensively with change of gauge.

Paramagnetic Resonance Absorption in Phenanthrene in Its Phosphorescent State

Roy W. Brandon, Roger E. Gerkin, and Clyde A. Hutchison

J. Chem. Phys. 41, 3717 (1964); http://dx.doi.org/10.1063/1.1725804 (10 pages) | Cited 46 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Electron paramagnetic resonance absorption in phenanthrene in its lowest photoexcited triplet state has been investigated at the boiling point of N2. The measurements have been made on phenanthrene molecules, oriented in diphenyl host crystals, at the frequency ∼2.3×1010 cycle sec—1 and also at lower frequencies at almost zero field (76 to 3 G). Taking the long principal magnetic axis in the plane of the phenanthrene molecule to be the x axis, the short axis in the plane to be the y axis, and the normal to the plane to be the z axis, the results have been described by the spin Hamiltonian,
math
where
math
A preliminary investigation of the hyperfine structure has been made. These results have been compared with published calculations.

Intensity Distribution for the X 1Σ+→A 1Π Transition in Carbon Monoxide Excited by Electron Impact

S. M. Silverman and E. N. Lassettre

J. Chem. Phys. 41, 3727 (1964); http://dx.doi.org/10.1063/1.1725805 (3 pages) | Cited 8 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The envelope shape for the unresolved X 1Σ+→A 1Π transition in carbon monoxide excited by electron impact has been experimentally determined at an incident electron energy of 508 V. The distribution has been compared with calculations using several published theoretical formulations from which the Franck—Condon factors may be obtained.

Knight Shifts and Relaxation Times of Alkali‐Metal and Nitrogen Nuclei in Metal—Ammonia Solutions

D. E. O'Reilly

J. Chem. Phys. 41, 3729 (1964); http://dx.doi.org/10.1063/1.1725806 (7 pages) | Cited 32 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
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:
math
math
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.

Spin Densities in Alkali‐Metal—Ammonia Solutions

D. E. O'Reilly

J. Chem. Phys. 41, 3736 (1964); http://dx.doi.org/10.1063/1.1725807 (7 pages) | Cited 19 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Wavefunctions for the alkali metal monomers of Li, Na, Rb, and Cs in liquid ammonia are calculated using a multipole expansion potential. The wavefunctions are made orthogonal to molecular orbital wavefunctions for the ammonia molecules surrounding the metal ion and spin densities at the metal, nitrogen, and hydrogen nuclei are calculated. A model is proposed for the cavity species which is exactly soluble within the same approximation. Spin densities are evaluated at nitrogen and hydrogen nuclei following orthogonalization to wavefunctions of ammonia molecules on the periphery of the cavity. Orthogonalization produces a large enhancement of spin density at nitrogen and a corresponding decrease in spin density occurs at hydrogen due to a node in the wavefunction produced by orthogonalization. The calculated spin density at the metal nucleus of the monomer and at nitrogen of the cavity species are in good agreement with experimental values. An explanation for the negative spin density at the protons is proposed.

Spin Hamiltonian for Cr III Complexes. Calculation from Crystal Field and Molecular Orbital Models and ESR Determination for Some Ethylenediammine Complexes

B. R. McGarvey

J. Chem. Phys. 41, 3743 (1964); http://dx.doi.org/10.1063/1.1725808 (16 pages) | Cited 43 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The spin Hamiltonians of Cr(en)33+ and trans‐CrCl2(en)2+ in single crystals of Co(en)3Cl3⋅3H2O, Co(en)3Cl3⋅NaCl⋅6H2O and trans‐[CoCl2(en)2]Cl⋅HCl⋅2H2O have been determined from the ESR spectra. In the case of the trans‐CrCl2(en)2+, ion it was found that the major axis for the spin—spin interaction lay along the C2 axis which is in the plane of the nitrogen atoms and rotates one ethylenediammine ring into the other. D and E for trans‐CrCl2(en)2+ were calculated from both a crystal field model and from the results of an extended Hückel molecular orbital calculation. It was found that both calculations give comparable results and give the best results when the spin—orbit coupling parameter of the free ion is used. In the case of the MO calculation, the results agree with experiment when the N☒Cr☒N bond angle in the ethylenediammine ring is chosen to be 84°. For trigonal complexes of Cr III, D was also calculated using a crystal field model and again it was found that the best results were obtained when the spin—orbit constant was that of the free ion. These calculations also showed that large changes in D and E can be expected for crystal field symmetries that allow for configuration interaction between the ground state and an excited quartet state. The theory for g in these complexes was also developed. In the case of the near octahedral complexes it has been shown that g can be simply related to the charge on the Cr atom in the eg bonding orbitals.

Vibrational Spectra and the Structure of Crystalline Triethylenediamine

Gerald S. Weiss, A. S. Parkes, Eugene R. Nixon, and R. E. Hughes

J. Chem. Phys. 41, 3759 (1964); http://dx.doi.org/10.1063/1.1725809 (9 pages) | Cited 18 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The crystal structure of the symmetric‐top molecule, triethylenediamine, is discussed in terms of the analysis of three‐dimensional x‐ray diffraction data in the space groups P63/m and P63. It was possible in the two cases to refine to slightly different structures with different molecular and site symmetries. The centrosymmetric structure with molecular symmetry D3h—mathm2 was used as the basis for an analysis of the infrared spectrum of the crystal and the assignment of the prominent bands. The Raman spectrum of the molecule in solution and the infrared spectrum of a crystalline monohydrate are also reported.

Structure of InSb at High Pressures

J. S. Kasper and H. Brandhorst

J. Chem. Phys. 41, 3768 (1964); http://dx.doi.org/10.1063/1.1725810 (5 pages) | Cited 23 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
It has been found by x‐ray diffraction studies at high pressure (∼30 kbar) that InSb occurs in a form other than the β‐Sn type which has been reported in previous studies. The new modification appears to have a simple orthorhombic structure with two atoms in the unit cell and can be derived from the β‐Sn structure by a simple shear process. While this structure may be a metastable one, it cannot be ruled out that it may be more stable than the β‐Sn form.
On the other hand, it is confirmed that the β‐Sn structure is readily obtained by quenching to 77°K and releasing the pressure, after the transformation has occurred in the vicinity of 30 kbar.

Polyelectrolytes : A Fuzzy Sphere Model

Marshall Fixman

J. Chem. Phys. 41, 3772 (1964); http://dx.doi.org/10.1063/1.1725811 (7 pages) | Cited 26 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The expansion factor α of polyelectrolytes is calculated on the assumption that at least one member of each interacting pair of charged segments is immersed in a segment cloud having the average sement density, here given by a uniform distribution inside a sphere. The counterion concentration is assumed to be much larger inside the sphere than the byion concentration, and a binding parameter is introduced via an effective dielectric constant. As a consequence α3 is predicted to be linear in the reciprocal square root of ionic strength. The dominant source of expansion is repulsion between segments such that one member of an interacting pair is inside and the other outside the background cloud. This same repulsion makes the free energy a minimum when the polymer shape is spherical.

Guest—Host Interactions: An Examination of the Solvent‐Induced Spectral Shift in a Model System

Huei‐Ying Sun, Stuart A. Rice, and Joshua Jortner

J. Chem. Phys. 41, 3779 (1964); http://dx.doi.org/10.1063/1.1725812 (8 pages) | Cited 13 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
In this paper we study the effect of a surrounding lattice of He atoms on the manifold of electronic states of the H2+ molecule‐ion. One‐center expansions of the molecular wavefunctions are employed, calculated by the Tibbs—Wannier method. The spherically averaged wavefunctions are in good agreement with the known exact solutions.
A detailed study of the environmental effect of the He lattice leads to the prediction of a blue shift of the first electronic transition, arising from a delicate balance between changes in the impurity excitation energy, Coulomb, exchange, van der Waals, and three‐center interaction terms. The signs of the various energy changes are rationalized in terms of the overlap charge density. These results are compared with previous treatments of environmental spectral shifts based on continuum models.

Electrical Conductivity of Low Dielectric Constant Liquids by dc Measurement

J. Gavis

J. Chem. Phys. 41, 3787 (1964); http://dx.doi.org/10.1063/1.1725813 (7 pages) | Cited 2 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
When conductivities of electrolyte solutions are very low dc measurements may be necessary to determine them. A quantitative criterion for when dc or ac may be used is given. Then a linearized partial differential equation for the transport of electric charge in low‐dielectric‐constant fluids, developed earlier by the author, is applied to the problem of dc conductivity measurements. In the absence of overpotentials at the low current densities usually employed boundary conditions on the transport equation are formulated in terms of charge densities in the solution near an electrode surface, and are related to potentials at the surface. The equation is solved to give expressions for the formation of the equilibrium double layer at the surface, and for the formation of the nonequilibrium double layer when the surface potential of one electrode is raised to cause current flow. From these the current—applied potential—time expression is derived. This consists of a transient polarization current which decays to a steady‐state current. The decay rate of the transient depends primarily upon the relaxation time of the solution. The steady‐state current obeys Ohm's law if the electrode spacing is large enough; conductivity may then be determined. If the spacing is too small diffusion enhanced transport occurs giving erroneously high apparent conductivities.

Nuclear Magnetic‐Dipole Coupling in Solid BF3

P. A. Casabella

J. Chem. Phys. 41, 3793 (1964); http://dx.doi.org/10.1063/1.1725814 (6 pages) | Cited 7 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The nuclear magnetic resonances of 11B and 19F have been studied in solid polycrystalline BF3 at 77°K. From a study of the 11B resonance, the 11B nuclear quadrupole coupling constant was found to be 3.045±0.060 Mc/sec. The 19F resonance possessed an unusual asymmetric structure that is explainable in terms of a magnetic‐dipole interaction between a 19F nucleus and its nearest‐neighbor 11B nucleus. An analysis of this interaction revealed that the observed asymmetry of the 19F resonance indicates that the 11B quadrupole coupling constant is positive. Furthermore, the width of the 19F resonance leads to a value of 1.29 Å for the distance between nearest‐neighbor boron and fluorine atoms in the solid in excellent agreement with the known values for BF3 gas.

Magnetic Properties of Gd☒Sc Alloys

H. E. Nigh, S. Legvold, F. H. Spedding, and B. J. Beaudry

J. Chem. Phys. 41, 3799 (1964); http://dx.doi.org/10.1063/1.1725815 (3 pages) | Cited 21 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Magnetic properties of some Gd☒Sc alloys have been measured. Paramagnetic to antiferromagnetic to ferromagnetic transitions were observed in the 69 at. % Gd alloy. Alloys of higher Gd content were ferromagnets and those of lower Gd content were antiferromagnets. The paramagnetic Curie temperatures decreased with decreasing Gd concentration. The effective number of Bohr magnetons per Gd atom showed a nearly linear increase with decreasing Gd concentration. Also the saturation magnetic moment per Gd atom increased with decreasing Gd concentration in the case of the ferromagnets.

ESR Studies and Covalent Bonding of Cyanide and Fluoride Complexes of Transition Metals

H. A. Kuska and Max T. Rogers

J. Chem. Phys. 41, 3802 (1964); http://dx.doi.org/10.1063/1.1725816 (4 pages) | Cited 15 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
ESR spectra of [Cr(CN)6]3— in dilute solid solution in K3Co(CN)6 single crystals have been obtained and the hyperfine splitting constants measured. These have been interpreted to provide values of the isotropic and anisotropic components As=—9.85±0.1 G and Ap=+0.65±0.2 G. The sigma and pi‐bond character of the metal—ligand bonds for [Cr(CN)6]3— and [CrF6]3— have been computed using molecular orbital theory and compared with the corresponding values for some other cyanide and fluoride complexes.

Dissociation Energies of Diatomic Molecules of the Transition Elements. II. Titanium, Chromium, Manganese, and Cobalt

Arthur Kant and Bernard Strauss

J. Chem. Phys. 41, 3806 (1964); http://dx.doi.org/10.1063/1.1725817 (3 pages) | Cited 66 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Using information derived from a combination of effusion and mass‐spectrometric techniques, the dissociation energy of Co2 has been calculated from the ratio of dimeric and monomeric cobalt in equilibrium with the liquid as D00(Co2)=39±6 kcal. Upper limits to the dissociation energy of Ti2, Cr2, and Mn2 are also estimated as D00(Ti2)<58 kcal, D00(Cr2)<44 kcal, D00(Mn2)<21 kcal. These results are correlated with the energy required to promote the atom to the lowest‐lying bonding or valence state of electron configuration 3dn—14s.

Phase Diagrams of Silicon and Germanium to 200 kbar, 1000°C

F. P. Bundy

J. Chem. Phys. 41, 3809 (1964); http://dx.doi.org/10.1063/1.1725818 (6 pages) | Cited 83 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The phase diagrams of Si and Ge have been investigated experimentally over a P, T range of about 200 kbar and 1000°C by observing electrical resistance behavior. For Si the boundary between the diamond cubic form and the metallic form extends from about 120 kbar at room temperature to about 150 kbar, 810°C, where melting occurs at the triple point. For Ge the corresponding boundary extends from about 115 kbar at room temperature to about 103 kbar, 600°C. A line drawn through the triple points for Sn, Ge, and Si, and extended, suggests that the diamond—metal—liquid triple point for carbon may be around 500 kbar, 2400°C. When the metallic forms are decompressed at room temperature they transform back to semiconducting forms different and more dense than the original diamond cubic forms. Upon heating these denser forms to a few hundred degrees at room pressure they transform to the usual diamond cubic forms. The absolute resistivity and temperature coefficient of resistance of metallic Ge has been determined.

Gaseous Diffusion in Porous Media. IV. Thermal Diffusion

E. A. Mason and A. P. Malinauskas

J. Chem. Phys. 41, 3815 (1964); http://dx.doi.org/10.1063/1.1725819 (5 pages) | Cited 11 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
The pressure dependence of thermal diffusion is derived on the basis of the ``dusty‐gas'' model, in which a porous medium is considered as a collection of giant molecules (dust particles) fixed in space. The results can also be applied to capillaries by suitable substitution for geometric parameters.
Thermal separation is zero at zero pressure and constant at high pressures, but the transition can be quite complex and varied, depending upon the temperature, molecular masses, and intermolecular forces of the gas molecules involved. Representative calculations have been made to illustrate the possibility of maxima and sign reversals of the thermal separation as a function of pressure. Comparison with the scanty available experimental results reveals no discrepancies, but further experiments are desirable, particularly for cases in which unusual transition behavior is expected.

Measurements of Thermal Dissociation of Hydrogen, Using Fast Protons

Grant J. Lockwood, Herbert F. Helbig, and Edgar Everhart

J. Chem. Phys. 41, 3820 (1964); http://dx.doi.org/10.1063/1.1725820 (5 pages) | Cited 34 times

Online Publication Date: 2 July 2004

Full Text: | Download PDF

Show Abstract
Experiments involving study of the angular scattering of kiloelectron‐volt protons from atomic and molecular hydrogen targets have been used to measure directly the fraction of hydrogen gas dissociated in equilibrium with hot tungsten. The state of the hydrogen gas in a tungsten furnace is determined by analyzing the scattered incident particles which result from single collisions between the incoming protons and the hydrogen gas in the furnace. In particular, the number of H— ions among the scattered particles is a measure of the molecular hydrogen density, since H— ions cannot be created in single collisions between protons and hydrogen atoms. Under the present experimental conditions it was possible to achieve a fraction dissociated of over 87.5% at a furnace temperature of 2380°K and still higher fractions at higher temperatures. These measurements are made at hydrogen pressures of the order of 10—2 Torr.
The practical conditions under which an atmosphere of highly dissociated hydrogen can be created are described and it is pointed out how the dissociation fraction and also the density of the hydrogen can be directly measured in the otherwise inaccessible interior of the gas. These measurements using a proton beam probe do not require that the pressure or temperature of the hydrogen be known and, in fact, do not require thermal equilibrium conditions.
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close