Volume 24, Issue 5, 01 May 1956
Index of content:
Nature of the Hydrogen Bond. III. The Measurement of the Infrared Absorption Intensities of Free and Hydrogen‐Bonded OH Bands. Theory of the Increase of the Intensity Due to the Hydrogen Bond24(1956); http://dx.doi.org/10.1063/1.1742717View Description Hide Description
The integrated intensities of the infrared OH bands of various compounds have been measured for the free and the hydrogen‐bonded states. It is found that the integrated intensity of either the free or the hydrogen‐bonded OH band increases as the frequency decreases. It is concluded that the main factor increasing the integrated intensity of the intermolecularly hydrogen‐bonded OH bands is the charge transfer through the hydrogen bond. The sign of the change of the dipole moment of the free phenol with the OH distance is discussed. An explanation is given for the weakness of the OH bands of the chelate compounds.
Calculation of the Detonation Properties of Solid Explosives with the Kistiakowsky‐Wilson Equation of State24(1956); http://dx.doi.org/10.1063/1.1742718View Description Hide Description
The Kistiakowsky‐Wilson equation of state,pVg = RT(1+xe βx ), where x = k/Vg (T+θ)α, for the gaseous detonation products of solid explosives has been re‐examined in the light of new experimental data on detonation pressure and on the variation of detonation velocity D with loading density ρ0 for several RDX/TNT mixtures. The value β = 0.30 used in the past is too high to match the observed slopes of the D—ρ0 curves. The old value α = 0.25 is too small to match the experimental Chapman‐Jouguet pressure of most of these explosives, but too large to match the pressure of pure TNT. A suitable compromise for the explosives considered is α = 0.5, β = 0.09, θ = 400°K.
Rate of Recombination of Radicals. I. A General Sector Theory; A Correction to the Methyl Radical Recombination Rate24(1956); http://dx.doi.org/10.1063/1.1742719View Description Hide Description
We have derived a rotating sector theory applicable to simple photochemical decompositions involving both first‐order and second‐order removal of radicals. This theory gives the behavior of radicals under intermittent illumination as a function of two parameters: α, the ratio of first‐ to second‐order removal rates, and β, a function of flash time. We use this theory to recalculate the experimental data on the methyl radical recombination rate. We find the constant k 2 to be 2.2×1013 cc moles—1 sec—1 in the temperature range 125°C to 175°C.
24(1956); http://dx.doi.org/10.1063/1.1742720View Description Hide Description
The rotating sector technique has been used to determine the rate of recombination of trifluoromethyl radicals produced by the vapor phase photolysis of hexafluoroacetone. Using the method of calculation described in Part I of this paper the rate constant was found to be 2.3×1013 cc mole—1 sec—1 at 127°C.
Study of Two‐Center Integrals Useful in Calculations on Molecular Structure. IV. The Auxiliary Functions C αβ γδε(ρ a ,ρb) for α≥024(1956); http://dx.doi.org/10.1063/1.1742721View Description Hide Description
A new method is developed for the numerical computation of the auxiliary functions C αβ γδε(ρ a ,ρ b ) which are used in (III) in this series, for the case α≥0. The present method is suitable for all values of the parameter τ = (ρ a —ρ b )/(ρ a +ρ b ), avoiding the excessive loss of significant figures which occurs in the methods developed in (III) for the physically important case of small τ.
24(1956); http://dx.doi.org/10.1063/1.1742722View Description Hide Description
A method is described for studying free radicals by absorption spectroscopy. The principal feature is the maintenance of an oscillating free radical concentration, which takes advantage of the high momentary concentrations that follow pulses of energy, and yet may be integrated to provide a continuous free radical absorption signal. The problems of detecting absorption in these transient systems are discussed using NH2 generated by an electrical discharge through ammonia as an example.
24(1956); http://dx.doi.org/10.1063/1.1742723View Description Hide Description
A mechanism for electron transferreactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex. Assuming such a mechanism, a quantitative theory of the rates of oxidation‐reduction reactions involving electron transfer in solution is presented. The assumption of ``slight‐overlap'' is shown to lead to a reaction path which involves an intermediate state X * in which the electrical polarization of the solvent does not have the usual value appropriate for the given ionic charges (i.e., it does not have an equilibrium value). Using an equation developed elsewhere for the electrostaticfree energy of nonequilibrium states, the free energy of all possible intermediate states is calculated. The characteristics of the most probable state are then determined with the aid of the calculus of variations by minimizing its free energy subject to certain restraints. A simple expression for the electrostatic contribution to the free energy of formation of the intermediate state from the reactants, ΔF *, is thereby obtained in terms of known quantities, such as ionic radii, charges, and the standard free energy of reaction.
This intermediate state X * can either disappear to reform the reactants, or by an electronic jump mechanism to form a state X in which the ions are characteristic of the products. When the latter process is more probable than the former, the over‐all reaction rate is shown to be simply the rate of formation of the intermediate state, namely the collision number in solution multiplied by exp(—ΔF */kT). Evidence in favor of this is cited. In a detailed quantitative comparison, given elsewhere, with the kinetic data, no arbitrary parameters are needed to obtain reasonable agreement of calculated and experimental results.
24(1956); http://dx.doi.org/10.1063/1.1742724View Description Hide Description
Various processes such as electron transferreactions,redox reactions at electrodes, and electronic excitation of dissolved ions may proceed by way of intermediate states whose electrical polarization is not in equilibrium with the field arising from the charges present. The usual expressions for the electrostaticfree energy and for the differential equation satisfied by the potential assume that the polarization and the field are in equilibrium. Accordingly, these equations are of but limited applicability to these processes. In the present paper equations are derived for various properties of systems having such nonequilibrium electrostatic configurations. These properties include the free energy, energy, and entropy of the nonequilibrium system, and the spacial dependence of the electrostatic potential. The free energy, for example, will be used to calculate the probability of formation of nonequilibrium states in certain problems of physical interest.
Normal Vibration Frequencies of CD3F. Structure of CH3F and CD3F from Infrared and Microwave Spectra24(1956); http://dx.doi.org/10.1063/1.1742725View Description Hide Description
The infrared absorptionspectrum of CD3F has been studied. Simultaneously, the infrared spectrum of CH3F was reinvestigated. Fundamental vibration frequencies for CD3F were found together with Coriolis coupling factors for the three degenerate vibrations in CH3F and CD3F. The fine‐structure analysis gave reliable values for the large rotational constants of CD3F and CH3F. The structure of the methyl fluoride molecule is discussed.
24(1956); http://dx.doi.org/10.1063/1.1742726View Description Hide Description
The exchange equilibria of the alkali ions Cs, K, Na, Li on attapulgite have been studied at 30° and 75°. Thermodynamic data for the systems have been calculated. Cesium is the most strongly adsorbed ion and the others follow in the order given. The specificity of the clay becomes lower at the higher temperature.
24(1956); http://dx.doi.org/10.1063/1.1742727View Description Hide Description
Improved infrared data have been obtained for benzene‐d 6 from 300—3700 cm—1 for both vapor and liquid phases. The frequencies can be interpreted very completely and satisfactorily. Good evidence was found for assigning v 14 and v 15 to 1287 and 838 cm—1 in benzene‐d 6. This provides valuable confirmation for Mair and Hornig's choice of 1310 and 1152 in benzene itself. All the fundamental frequencies for both benzene and benzene‐d 6 now seem to be well established, aside from small uncertainties in a few cases where the values have been inferred from combination tones or from the product rule.
The infrared spectrum of benzene vapor for the range 300—700 cm—1 is also given.
24(1956); http://dx.doi.org/10.1063/1.1742665View Description Hide Description
The infrared absorption intensities of the fundamental vibration bands of BF3 have been measured and vibrational bond moments μ and their derivatives ∂μ/∂r determined. In the A 2″ class, μBF=1.7 D; in the E′ class μBF=0.9 or 2.6 D, ∂μ/∂r = —6.1 or +4.0 D/A.
Inspection of the form of the bending modes suggests that deviations from the bond moment approximation occur such that μ(A 2″) <μ(static) <μ(E′). The solution μ(E′) = 2.6 D is therefore preferred.
Re‐examination of the data of Schatz and Hornig on CF4, SiF4, and SF6 in the light of the present results shows that the vibrational bond moments in these molecules are: μCF∼2.4, μSiF∼3.3, μSF∼2.7 D. These moments are roughly equal to Δr 0, where r 0 is the bond length and Δ the electronegativity difference between the atoms in the bond.
The available data on μ and ∂μ/∂r for the C–F bond in various molecules are compared and briefly discussed.
Infrared Spectrum and Molecular Constants of Carbon Dioxide. Part II. Levels 10°0 and 02°0, 10°1 and 02°1 Coupled by Fermi Resonance24(1956); http://dx.doi.org/10.1063/1.1742666View Description Hide Description
Absorption bands of carbon dioxide involving the Fermi diads 10°0, 02°0 and 10°1, 02°1 have been investigated and molecular constants obtained. The variation in the centrifugal stretching constants which has been observed in the component levels is such that the average centrifugal stretching constant of the diad is very nearly the same as that of the vibrationless ground state of CO2.
24(1956); http://dx.doi.org/10.1063/1.1742667View Description Hide Description
Each of the two polymorphic forms of pure tin were found to produce different chemical compounds when reacted with concentrated hydrochloric acid under identical conditions. These findings were established by x‐ray diffraction and chemical analysis. The metallic form of β white tin combined as Sn++, whereas the semiconducting form of α gray tin combined as Sn++++. This chemical behavior was found to be consistent with the electronic configuration of the valence electrons ascribed to each form of the tin atom.
24(1956); http://dx.doi.org/10.1063/1.1742668View Description Hide Description
Analysis of the Zeemanquadrupolespectra of Cl35 in single crystals of p‐chloroaniline and p‐chlorobenzylchloride yields the following information: There are two sets of chlorine atoms in the p‐chloroaniline crystal with differently oriented electrical field gradients. The angle between the field gradient z‐axes is 79°±1°; the y‐axes are parallel. Both field gradients have the same asymmetry, η=0.06±0.03. In p‐chlorobenzylchloride there are four sets of chlorines (attached directly to the ring) which have differently oriented field gradients. The z‐axes are parallel to the edges of a rectangular pyramid with apex angles of 8° and 67°, both ±1°. All four have the same asymmetry, η=0.07±0.02.
The bond between the chlorine and the ring is calculated to have 2.0±1.0% double bond, 79±10% single bond and 19±10% ionic character in p‐chloroaniline; 2.4±0.7% double bond, 80±10% single bond and 17±10% ionic character in p‐chlorobenzylchloride. The large uncertainty in the single bond and ionic characters results from the uncertainty in the hybridization of the chlorine bonding orbital.
24(1956); http://dx.doi.org/10.1063/1.1742669View Description Hide Description
The infrared spectrum of C2Br4 in various solvents and as a liquid has been observed and measured in the range 3—100μ. The new data, in conjunction with earlier results and force constant calculations, have enabled for the first time an essentially complete and satisfactory vibrational assignment. The fundamentals, in units of cm—1, are 1535, 265, 144 in a 1g ; 880, 208 in b 1g ; 766, 119 in b 2u ; 635, 188 in b 3u ; 66 in a 1u ; 245 in b 1u ; and 464 in b 2g . The present results for C2Br4 have required that two changes be made in the earlier assignment for C2Cl4. The angular modes of the chloro compound in b 1u and b 3u are now found to be at 288 and 310 cm—1, respectively. The assignments for C2F4, C2Cl4, and C2Br4 are then complete and concordant.
24(1956); http://dx.doi.org/10.1063/1.1742670View Description Hide Description
Sensitive resonant cavity techniques were used to search for dielectric loss in the lower members of the saturated hydrocarbon series, C 1 through C 5, at several frequencies in the range 2 to 24 kMc/sec. No detectable loss was found in methane (tanδ<8×10—7) or ethane (tanδ<4×10—7) up to the highest pressures examined, 69 and 36 atmos, respectively. Significant loss attributable to the presence of small permanent dipole moments was found in propane, isobutane, and isopentane. The results for isobutane, which show nonresonant or Debye type absorption characteristic of a symmetric top inversion spectrum having ``zero'' frequency, lead to an accurate evaluation of the dipole moment, namely 0.132 D. The effective collision diameters for impacts governing the Debye relaxation in both isobutane and isopentane are larger than the kinetic collision diameters.
24(1956); http://dx.doi.org/10.1063/1.1742671View Description Hide Description
Self‐diffusion in liquidgalliummetal at atmospheric pressure is described by the equation: D = 1.07 × 10—4 exp[—1122/RT] cm2 sec—1. At 30°C the effect of pressure on the rate of self‐diffusion is given by: log10 D = —4.7793—9.529×10—6 P (kg cm—2). The activation volume at this temperature is 0.55 cm3 g atom—1. Although the Stokes‐Einstein radius agrees quite well with the ionic radius of Ga+3, the temperature coefficients of viscosity and diffusivity differ somewhat.
24(1956); http://dx.doi.org/10.1063/1.1742672View Description Hide Description
The infrared spectra of gaseous and solidGe2H6 have been studied in the spectral region 400—4000 cm—1. The infrared‐active fundamental frequencies are as follows: A 2u : 2078, 755; Eu : 2114, 898, and 407 cm—1. Assignment of combination bands gives the remaining fundamentals: A 1g : 2070, 765, 229; A 1u : 144; Eg : 2150, 875, and 417 cm—1. From the torsional frequency, a cosine barrier to internal rotation is 1200 cal. The structure of the perpendicular band at 898 cm—1 has been resolved, giving information connecting the Coriolis constant for this vibration with the molecular structure parameters.
The spectrum of the solid, obtained at 90°K, shows only those fundamentals active in the gas phase. Small splittings or satellites are observed, and possible crystal symmetries are suggested.
24(1956); http://dx.doi.org/10.1063/1.1742673View Description Hide Description
The products of acetylene photolysis at 1849 A were found to be a polymer resembling cuprene, hydrogen, ethylene, diacetylene, vinylacetylene, and benzene. The relationships of the quantum yields of these products to pressure of acetylene suggest that both free radicals and excited acetylene molecules are involved in the photolytic mechanism. This suggestion is strongly supported by the nature of the absorptionspectrum, since in this wavelength region, the absorption is partly discrete and partly continuous.