Index of content:
Volume 29, Issue 1, 01 July 1958
29(1958); http://dx.doi.org/10.1063/1.1744455View Description Hide Description
The sputtering of silver by the ions H+, H2 +, and D+ has been measured by allowing a magnetically analyzed beam of ions from an RF source to strike a target containing radioactive silver. The angular distribution of the sputteredsilver follows approximately a cosine law. At normal incidence and 9250 volts energy, the number of atoms sputtered per incident ion is 0.03 for H+, 0.075 for H2 +, and 0.08 for D+. These values are much lower than those of previous workers, and the difference is ascribed to the absence of atoms and excited molecules from the analyzed ion beams.
29(1958); http://dx.doi.org/10.1063/1.1744464View Description Hide Description
When the unanalyzed beam from a radiofrequency ion source strikes a silver target, sputtering is caused by both the ions and the neutral particles in the beam. The sputtering due to neutrals alone has been measured by removing the ions from the beam magnetically. For a beam of 40 μA at normal incidence and 10 kv energy, in the case of hydrogen over 90%, and in the case of helium about 50% of the sputtering is due to neutrals.
29(1958); http://dx.doi.org/10.1063/1.1744469View Description Hide Description
Ultrasonicabsorption in MnSO4 solutions has been studied in great detail in the frequency range 1–6 Mcps., at concentrations varying from 0.0025 to 1 molar. The relationship between the excess sound absorption and the concentration is found to be linear from 0.02 to 0.1 molar, but becomes nonlinear both below 0.02 and above 0.1 molar. The frequency behavior of the excess sound absorption can be represented by a relaxation curve at about 3 Mcps. The mechanism responsible for excess sound absorption is of the dissociation type and is supported by the study of the influence of the dielectric constant of the solvent on the absorption and the temperature shift of the relaxation frequency.
29(1958); http://dx.doi.org/10.1063/1.1744414View Description Hide Description
An isothermal equation of state is derived from the Coulomb virial theorem for ``simple'' metals consisting of imperturbable (i.e., invariant) kernels embedded in a uniform sea of valence (e.g., s) electrons. Comparison with experiment at room temperature gives good agreement for the alkali and alkaline earth metals, but is understandably erratic for other groups. The compressibility is simply related to the heat of formation of the normal gaseous ion kernel.
29(1958); http://dx.doi.org/10.1063/1.1744418View Description Hide Description
Results of dielectric constant and loss measurements on a range of aqueous and alcoholic electrolytes at wavelengths of 1.25, 3.2, 9.9, 17, and 51.5 cm from 3°C to 25°C are analyzed in terms of dielectric constant depression, relaxation time depression and spread, and conductivity elevation. The small relaxation time spread (α∼0.02) is interpreted as being due to hydrogen bond bending, the relaxation time depression as bond breaking, and the dielectric constant depression as restriction of dipole rotation by the ions. The conductivity elevation is believed to be an effect of the same type as that observed by Little and Smith.
It is shown that the alcohol dielectric constant depression is too large to be interpreted in terms of dipole restriction by solvation so that the ion must have a marked effect on the alcohol structure.
29(1958); http://dx.doi.org/10.1063/1.1744454View Description Hide Description
We have calculated the cross section for excitation of the first vibrational level in the collision of two hydrogen molecules in the ground state. A partial wave analysis is used, and the radical equation is solved for many values of angular momentum using the high speed computer Univac. We find that the major contribution to the total cross section comes from large values of the angular momentum, of the order of 10 to 20, and that values of the angular momentum up to about 80 must be considered. In the energy range of interest, 0.5 to 2 ev, the total cross section is obtained, and the vibrational relaxation time is also computed. The value of the cross section is found by calculation to be very sensitive to the precise values of the intermolecular potential used.
29(1958); http://dx.doi.org/10.1063/1.1744456View Description Hide Description
Electron spin resonance at 3.2 cm has been observed from copper(II) in single crystals of copper(II) bis‐acetylacetonate diluted to ½ mole % with palladium(II) bis‐acetylacetonate at 77°K and 300°K. The parameters of the spin Hamiltonian have been expressed in terms of the atomic orbital coefficients of molecular orbital wave functions describing the electron hole in the orbital ground state and two excited states. Experimental determination of the spin Hamiltonian then results in expressions for the molecular orbital wave functions. The results indicate that the in‐plane sigma and pi bonding are appreciably covalent, whereas the out‐of‐plane pi bonding with the acetylacetonate ring is ionic.
The hyperfine interaction may be expressed by a relation of the type , where C 2 increases with decreasing temperature. The appearance of the term in is attributed to low symmetry crystal fields due to the crystallographic array, the main symmetry being determined by the molecule itself. A small amount of rhombic character was observed in the gtensor, but was not enough to make an accurate location of the gx and gy directions possible. For the purpose of analysis, the g factor is expressed in terms of the two principal values g∥ and g ⊥ which do not vary between 77°K and 300°K to the accuracy of the determination.
29(1958); http://dx.doi.org/10.1063/1.1744457View Description Hide Description
The electron spin resonance at 3.2 cm has been observed for single crystals of copper(II) bis‐salicylaldehyde‐imine diluted to ½ mole percent with the corresponding nickel chelate. Analysis of the spectrum by methods given in the preceding article indicate that the sigma bonding and in‐plane II‐bonding are appreciably covalent, whereas the out‐of‐plane π bonding is ionic. Hyperfineinteractions in addition to that resulting from the copper nucleus were observed and shown to be attributable to interactions with the nitrogen nuclei adjacent to the copper ion and with the two protons bonded to the carbon atoms directly adjacent to the nitrogen atoms. The two protons bonded directly to the nitrogen atoms do not contribute to the hyperfineinteractions. Bonding information obtained from the magnitude of the hyperfineinteraction due to the nitrogen nucleus agrees with that obtained from the gtensor and hyperfineinteraction of the copper nucleus.
In addition structural information about nickel(II) bis‐salicylaldehyde‐imine is obtained. The Ni‐O distance is 1.92±0.07 A while the Ni‐N distance is 1.94±0.05 A. The angle between these bonds is found to be 93±3°.
29(1958); http://dx.doi.org/10.1063/1.1744458View Description Hide Description
When hydrogen is dissociated by an incandescent tungsten filament in a glass tube, some of it is cleaned up if the tube is cooled in liquid air. The amount cleaned up can be greatly increased by coating the inner wall with mercury or copper. In one experiment the amount cleaned up in cold mercury was equivalent to 14 monolayers of atomic hydrogen. The cleanup proceeded at a diminishing rate until the pressure fell to the value at which hydrogen left the mercury as fast as it entered. When hydrogen was cleaned up in a very thin coating of mercury there were 1.5 to 1.8 atoms of mercury per atom of hydrogen. All the cleaned‐up gas was recovered when the tube was brought to room temperature. After cleanup in copper there was little recovery until the temperature rose above —150°K.
29(1958); http://dx.doi.org/10.1063/1.1744459View Description Hide Description
The problem of isotropic hyperfineinteractions in the EPRspectra of aliphatic free radicals is approached from the molecular‐orbital picture of hyperconjugation. The ethyl, methylethyl, and 1,1‐dimethylethyl radicals are treated by this approximation; with a reasonable choice of parameters, the results can be correlated rather well with our present knowledge of aliphatic radicals. The calculated coupling constants of methyl group hydrogens are of the order of 15 to 25 gauss, do not decrease radically with the presence of additional methyl groups, and are very nearly proportional to the molecular‐orbital unpaired electron density at the central carbon atom.
29(1958); http://dx.doi.org/10.1063/1.1744460View Description Hide Description
Total absorption coefficients of furan vapor were determined in the region from 1050 to 2150 A by a photoelectric method, and photoionization coefficients in the region from 1050 to 1400 A with an ion chamber. A reassignment of the absorption bands in the region from 1400 to 1700 A yielded two Rydberg series converging to 8.89 ev in agreement with the ionization potential obtained by photoionization measurements. Another Rydberg series was found to converge to 9.95 ev corresponding probably to the removal of an inner π electron of furan.
29(1958); http://dx.doi.org/10.1063/1.1744461View Description Hide Description
Reaction rate kinetics is applied to the phenomenon of phase change. Two rate constants, one for nucleation and the other for growth processes, are embodied in the theory. These microscopic parameters are of a basic nature, with a significance quite distinct from the macroscopic quantities employed by Johnson‐Mehl and Avrami (JMA) in the conventional phenomenological formulation. Expressions for the nucleation rate and the degree of transformation are established once the basic properties of the Poisson exponential binomial limit distribution have been determined. The statistical kinetic theory does indeed lead to a sigmoid‐shaped transformation curve commonly observed in phase changes. An essential ingredient of the present theory, not incorporated in the JMA phenomenological theory, is the role of nuclei and specimen size; unusual behavior may be expected in small particles undergoing transformation.
Changes in the Near Ultraviolet Spectrum of Crystalline Hexamethylbenzene Accompanying a Low Temperature Phase Transition29(1958); http://dx.doi.org/10.1063/1.1744462View Description Hide Description
The hexamethylbenzene crystal undergoes a phase transition at 110°K. The near ultraviolet absorption spectra of single oriented crystals of this substance have been studied in polarized light in the neighborhood of the transition temperature. A drastic and discontinuous change of the spectra is observed to accompany the phase change. The spectral change at the transition point is interpreted as indicative of a distortion of the molecule such that only twofold axes remain.
29(1958); http://dx.doi.org/10.1063/1.1744463View Description Hide Description
The formation of stabilized free‐radical mixtures by the low‐temperature condensation of gases containing such species is considered. A primary concern is the amount of free radicals resulting from such a process.
The over‐all process of formation of condensed phase stabilized free‐radical mixtures involves the original means of their production as gases, the recombination of free radicals as the gaseous mixtures are transported to the seat of condensation, and the recombination which occurs in the immediate vicinity of and within the condensed phase which is formed. For the present purpose only the latter aspect is considered in any detail, the effects of production and prior recombination being summarized in a stated composition for the condensing gas. For simplicity, only mixtures consisting of a single species of atomic free radicals, diatomic molecules which may be formed from their recombination, and inert atomic species are treated.
The basis for stabilization is taken to be isolation. Thus, those condensed phase mixtures are regarded as stable which do not permit free radicals to come in contact with one another. It is assumed, therefore, that condensation occurs at a temperature sufficiently low to render the effect of diffusion negligible. Such recombination which does occur is presumed to do so as a result of the juxtaposition of the atomic free radicals.
Several models of the stabilization process are considered from a statistical viewpoint. In each instance no explicit reference is made to the kinetics of the recombination process. The effects of coordination number, surface condensationversus bulk condensation,condensation coefficient and clustering are treated. In each of the models the dependence of the condensed phase composition upon the gas phase composition and the statistical properties of the constituents is determined.
Substituted Methanes. XXVIII. Infrared Spectral Data and Assignments for CHCl2F and CHClF2 and Potential Energy Constants and Calculated Thermodynamic Properties for CHCl2F, CDCl2F, CHClF2, and CDClF229(1958); http://dx.doi.org/10.1063/1.1744465View Description Hide Description
Infrared spectral data were obtained with NaCl and CsBr prisms for gaseous CHCl2F and CHClF2 from 270 to 4000 K (K=kayser=wave/cm) and the observed absorption bands were assigned to the vibrational modes for both molecules. Using the Wilson FGmatrix method, reasonable values of the F‐matrix elements were found which reproduced the observed wave numbers to within 2%. These were then used to calculate the wave numbers corresponding to the fundamental vibrations of CDCl2F and CDClF2. Also, these F‐matrix elements and analytical expressions obtained from the theory of Gold, Dowling, and Meister were used to get values of the f‐matrix elements (potential energy constants). Having tested the assignments by the normal coordinate treatments, the observed wave numbers for CHCl2F and CHClF2 were then used to calculate the enthalpy function, the free energy function, the entropy, and the heat capacity for 1 atmos pressure and for 12 temperatures from 100 to 1000°K, to a rigid rotor, harmonic oscillator, ideal gas approximation. Since the calculated wave numbers for CDCl2F and CDClF2 should be reliable to within about 2%, these were used in similar thermodynamic calculations to establish tentative values of the thermodynamic functions for these molecules.
Theoretical Investigations on the Light Scattering of Colloidal Spheres. IV. Specific Turbidities in the Lower Microscopic Range and Fine Structure Phenomena29(1958); http://dx.doi.org/10.1063/1.1744466View Description Hide Description
Additional calculations were carried out on the scattering cross sections of spheres and the specific turbidities of their dispersed systems using again the Mie theory. The parameters considered were α=7.0 (0.2) 25.6 and m=1.05 (0.05) 1.30. The close spacing of the α values allowed the detection of a fine structure of regular period in the (τ/c)0(α) curves and related curves. The fine structure is explained as the result of interferences of secondary magnitude.
Neighbor Interactions and Internal Rotations in Polymer Molecules. I. Stereospecific Structure and Average Dimensions29(1958); http://dx.doi.org/10.1063/1.1744467View Description Hide Description
The skeletal bonds of vinylic polymer molecules are classified as (+) bonds and (—) bonds according to the arrangement of the side groups relative to the bonds. The detailed structure of isotactic and syndiotactic polymers is characterized by the different regularities of arrangement of these two bond types along the molecular chain. Symmetry properties of (+) and (—) bonds, and of (+) (+), (—) (—), and (—) (+) bond pairs, are discussed. These lead to relations between the average values of functions of the internal‐rotation angles of the various bond‐pairs.
The end‐to‐end distance of isotactic and syndiotactic molecules is expressed in terms of bond lengths, bond angles, and internal rotation angles of the skeletal bonds, using methods of matrix algebra. The mean‐square end‐to‐end distance 〈h 2〉 of these molecules is determined by certain averages of trigonometric functions of the internal rotation angles enclosed between neighboring skeletal bond pairs. The averages depend on the energy of interaction of neighboring side groups as well as on the internal interactions within the skeletal bonds, and are different in the isotactic and syndiotactic molecules.
29(1958); http://dx.doi.org/10.1063/1.1744468View Description Hide Description
The influence of the interaction between neighboring ionizable groups of a polyelectrolyte molecule on the internal rotations around its skeletal bonds is considered. It is found that the repulsion between neighboring groups tends to contract the molecule by twisting the molecular chain, and acts therefore against other forces which tend to extend the molecular dimensions.
The quantitative analysis is based on calculating a grand partition function of the polyelectrolyte molecule, in which both the energy of interactions within each bond and the energy of interaction between neighboring ionizable groups are expressed as functions of the internal rotation angles. The grand partition function is used in obtaining the various averages of the trigonometric functions of the internal rotation angles which determine 〈h 2〉 according to the results of the previous paper (Part I). These averages are given as functions of the degree of ionization of the macromolecule.
The effect of the internal rotation of the skeletal bonds on the potentiometric titration and buffering capacity of polyelectrolyte solutions is discussed.
29(1958); http://dx.doi.org/10.1063/1.1744470View Description Hide Description
Hindrance to rotation of hydrogen molecules in the adsorbed state is discussed. The possibility is pointed out that in some cases the lowest para‐level may lie close to the lowest ortho‐level. It is proposed that a simple adiabatic cooling method be obtained by allowing adsorbed parahydrogen to convert to equilibrium hydrogen at low temperatures under adiabatic conditions. It is shown that very low temperatures might be obtained under favorable conditions by relatively simple means.