Index of content:
Volume 27, Issue 3, 01 September 1957
27(1957); http://dx.doi.org/10.1063/1.1743796View Description Hide Description
Chemical etches have been found which polish or remove thick surface layers from PbS crystals. One of these etches results in the formation of etch pits. The dissolving action of this etch on PbS, PbSe, and PbTe and the etch pit patterns formed by it on natural and synthetic PbS crystals are discussed.
27(1957); http://dx.doi.org/10.1063/1.1743797View Description Hide Description
A quantitative reinvestigation of the pressure broadening in the γ(0,0) and γ(1,0) bands of nitric oxide has established that the pressure effect is not abnormal as has sometimes been supposed and that the collision diameter of the excited NO molecule is approximately 3.8 A.
27(1957); http://dx.doi.org/10.1063/1.1743798View Description Hide Description
The second π‐ionization potentials, corresponding to the process R+→R+++e, are calculated for a number of unsaturated hydrocarbon molecules R. The SCF LCAO molecular orbital method, together with semiempirical values proposed by Pariser and Parr and Hush and Pople for interaction and core integrals, has been employed. The value obtained for benzene (16.9 ev) is in good agreement with that reported by Hustrulid, Kusch, and Tate (17.2±1.0 ev).
27(1957); http://dx.doi.org/10.1063/1.1743799View Description Hide Description
Mass spectra and appearance potentials have been determined for methanol, ethanol, and propanol. These data are used in semiempirical application of the statistical theory of mass spectra. The theory facilitates assignment of plausible mechanisms for the production of the various ion fragments. It is possible to obtain computed spectra in agreement with experimental data using an internally consistent set of structural parameters.
27(1957); http://dx.doi.org/10.1063/1.1743800View Description Hide Description
The existing theoretical interpretation of the activation energy for viscous flow in terms of the intermolecular potential is discussed in the light of the Born‐Green theory. This theory suggests the possibility of an absolute calculation of the activation energy. A simplified treatment affords results of the right order of magnitude.
27(1957); http://dx.doi.org/10.1063/1.1743801View Description Hide Description
The complex dielectric constants of ethylene, diethylene, triethylene, tetraethylene, and hexaethylene glycols in the liquid state have been measured at frequencies of 1.43, 9.73, and 18.7 kmc/sec at temperatures from 5 to 50°C. The parameters of dielectric relaxation for these polyethylene glycols have been calculated from the complex dielectric constants and the static dielectric constants by the circular arc rule of Cole and Cole. It has been found that the dielectric relaxation times obtained do not vary much with the homolog of this polyethylene glycol series, being of the order of 10—10 sec at 20°C. The value of relaxation time is the largest for diethylene glycol, decreasing slightly with higher homologs of this series. This striking feature is discussed in terms of flexibility of the polyoxyethylene chain due to internal rotation around the C–O bonds of the chain skeleton, which would make more possible a partial and independent orientation of the hydroxyl groups at the ends of the molecular chain in the case of higher polyethylene glycols.
Rates and Mechanisms of Protolysis of Methylammonium Ion in Aqueous Solution Studied by Proton Magnetic Resonance27(1957); http://dx.doi.org/10.1063/1.1743802View Description Hide Description
The application of the nuclear magnetic resonance technique to the study of fast protolysis reactions of methylammonium ion in water is described. It is shown that reaction rates can be measured quantitatively for half‐times in the range, 0.002 to 0.2 sec. Reaction rates were measured as a function of the methylammonium ion concentration and of the hydrogen ion concentration. Detailed information on the reaction mechanism was obtained by correlating the rate constants obtained from the CH3, the NH3 + and the H2O lines of the NMR spectrum. In the pH range employed (between 3 and 5), the exchange rate is very nearly proportional to [CH3NH3 +][CH3NH2], the second‐order rate constant being 6×108 sec—1 M —1 at 19°. Two separate reactions contribute to this rate constant: One of them, which accounts for about 40% of the total rate, is a direct proton transfer from CH3NH3 + to CH3NH2. The other involves also at least one molecule of water, CH3NH2 receiving a proton from the solvation shell of CH3NH3 + while simultaneously, or soon thereafter, a proton is transferred from CH3NH3 + to the solvation shell.
27(1957); http://dx.doi.org/10.1063/1.1743803View Description Hide Description
Acid‐base equilibria in aqueous solutions of methylamine, dimethylamine, and trimethylamine have been studied by nuclear magnetic resonance. It is shown that the chemical shift of the methyl protons is a linear function of the concentration ratio of acid to base plus acid. The NMR spectrum of tetramethylammonium ion is also given.
27(1957); http://dx.doi.org/10.1063/1.1743804View Description Hide Description
The thermodynamic properties of the alkali halides in the gas phase have been computed for the temperature range 298.16°K to 2000°K. These data are applied to the determination of the dimer concentration in the gas. It is concluded that there is very little dimer and/or higher polymer in the gas, in agreement with previous infrared spectroscopic studies.
27(1957); http://dx.doi.org/10.1063/1.1743805View Description Hide Description
An investigation of the adsorption of nickel on molybdenum is compared with theoretical considerations of adsorption phenomena. Nickel was found to adsorb coherently on molybdenum, preferentially on the (111) planes of the substrate. For coverages of about ⅕ of a monolayer, the following activation energies were determined:The desorption energy did not vary with degree of completion. Heavy adsorbed layers of nickel were investigated. The equilibrium position of heavy layers was found to be field dependent.
27(1957); http://dx.doi.org/10.1063/1.1743806View Description Hide Description
The kinetics of the isotopic chlorine exchange between SiCl4 and HCl have been measured using the tracer Cl36. The reaction is first order in HCl and second order in SiCl4. E‡ and S‡ are 22.4 K cal mole—1 and —17.6 cal deg—1 mole—1, respectively. A mechanism for the exchange is proposed.
27(1957); http://dx.doi.org/10.1063/1.1743807View Description Hide Description
The solid phases of ordinary methane were studied under pressure at low temperatures by the volume discontinuity method. The phase diagram of the solid is presented. A new phase was observed, and the ``missing'' phase (by analogy to CD4 and CD3D) evidently appears only under pressure at liquid helium temperatures. Observations indicate another phase at high pressures in the low‐temperature region. Indications of correlations among the phase diagrams of CH4, CH3D, and CD4 are shown.
27(1957); http://dx.doi.org/10.1063/1.1743809View Description Hide Description
The infrared spectrum of PCl5 in the vapor state and as a solution in CS2 has been obtained. The Raman spectrum of a solution of PCl5 in benzene has been obtained photoelectrically together with depolarization ratios. A complete vibrational assignment has been made on the basis of D 3h symmetry, and force constants have been calculated. Thermodynamic functions have been computed from the assigned fundamentals and used to interpret the equilibrium of the reaction PCl3(g)+Cl2(g)=PCl5(g) giving ΔE 0 0=—20 525±160 cal mole—1.
27(1957); http://dx.doi.org/10.1063/1.1743810View Description Hide Description
The infrared spectra of solid Hg(CN)2 and the mono‐ and di‐substituted C13 and N15 species have been observed. The polarized spectrum of a single crystal of the normal species was also observed. The seven fundamental vibrations of the linear, symmetric Hg(CN)2 molecule have been assigned at 2192, 415, 2193.5, 442, 276, 341, and ca 100 cm—1.
From the observed frequencies of the normal and isotopic species, force constants were calculated for two possible structures: N–C–Hg–C–N and C–N–Hg–N–C. It is shown that the latter structure gives unreasonably large values for the CN stretching force constant (> 20 md/A) and the CN, HgN interaction constant (∼2.4 md/A), while the former structure yields quite reasonable force constants, namely: Fcn=17.6, Fhgc=2.61, Fcn, c′n′=—0.1, Fhgc, hgc′=0.1, and Fhgc, cn=0.1 md/A. These results are presented as strong evidence that the cyanides are bound to the mercury through carbon atoms.
27(1957); http://dx.doi.org/10.1063/1.1743811View Description Hide Description
The rates of exchange of NH3 between solventliquid ammonia and ligand ammonia in five metal‐ammine cations have been measured with N15 labeling. Reactants were separated by distilling off the solvent ammonia. Within the exchange times of 0.5, 3, and 11 minutes, respectively, exchange is complete for Ag(NH3)2 +, Cu(NH3)4 +2, and Ni(NH3)6 +2 at concentrations of ca 0.01 f and in the dark at —33.5°C. Based on a single run, exchange with 0.013 f Cr(NH3)6 +3 in the dark at 25.0°C exhibited a good McKay plot with a half‐time of 1500 minutes, corresponding to a bimolecular rate constantk=1.3×10—6 l·mole—1·sec—1. Exchange with Co(NH3)6 +3 was shown to be slow (half‐times of the order of several hours at 0.002–0.005 f in the dark at 25.0°C), but reproducible results were not obtained. All complexes were studied as the nitrates. The observed slow exchange for Cr(NH3)6 +3 and Co(NH3)6 +3 is consistent with their classification as ``inert inner‐orbital'' complexes.
Exchange of N15 between NO3 — and solventliquid ammonia, including exchange during the hot NaOH treatment used to distill off the ammonia, is less than 3% at 0.05 f NO3 — and 25°C.
27(1957); http://dx.doi.org/10.1063/1.1743812View Description Hide Description
Study of the Wurtzite‐Type Binary Compounds. II. Macroscopic Theory of the Distortion and Polarization27(1957); http://dx.doi.org/10.1063/1.1743813View Description Hide Description
The slight departure of wurtzite‐type binary compounds from ideal c/a ratio and ideal sublattice displacement parameter u is accounted for by the forces arising from partial polar binding. These long‐range forces are calculated in terms of a postulated charge ±fe per ion and certain lattice sums which we evaluate. When balanced against the elastic,piezoelectric, and dielectric constants of the crystal, the forces account for both the direction and the order of magnitude of the distortion. The compounds AlN, BeO, and ZnO are considered in detail. An experimental value of 8.5 is given for the dielectric constant of AlN, but in the absence of precise values for elastic and piezoelectric constants only an order of magnitude check of the theory can be made at this time. Some remarks are appended on the general problem of finite lattice sums in complex lattices which have dipole and/or quadrupole moments in the unit cell.
27(1957); http://dx.doi.org/10.1063/1.1743814View Description Hide Description
The infrared spectra of the following compounds have been investigated: microcrystalline NaNO2, KNO2, and AgNO2; and aqueous solutions of NaNO2 and KNO2. The spectra of N15‐labeled compounds have also been obtained. The spectrum of the high‐temperature modification of NaNO2, which exists above 160°, has been observed. The fundamental frequencies for NO2 — (in crystalline NaNO2) are: . These are used to calculate the following force constants, in units of millidynes/A: .
27(1957); http://dx.doi.org/10.1063/1.1743815View Description Hide Description
The polarized infrared spectra of Rochelle salt from 4550 cm—1 to 8100 cm—1 have been observed with a grating spectrometer. These spectra and the Raman spectra reported by other authors have been partially interpreted. Tentative conclusions concerning the location of the hydrogen atoms in the crystal at a temperature of 300°K are drawn from the analysis of the spectra.