Index of content:
Volume 23, Issue 2, 01 February 1955
23(1955); http://dx.doi.org/10.1063/1.1741944View Description Hide Description
The increase in fluorescence yield of β‐naphthylamine vapors in the presence of foreign gases provides a new powerful method for studying energy exchange. The effect, discovered by Neporent, is analyzed kinetically and the analog of the Stern‐Volmer equation for this effect is derived. Neporent's data are recalculated in the light of this analysis.Fluorescence stabilization by deuterium and sulfur hexafluoride is studied experimentally following the procedure of Neporent. It is concluded, in particular, that the vibrational and rotational modes of the hydrogen molecules are inactive in the excitation or de‐excitation of vibrational energy of complex molecules.
23(1955); http://dx.doi.org/10.1063/1.1741945View Description Hide Description
Infrared spectroscopic studies of naphthalene and naphthalene‐d 8 are reported as follows: (a) far infrared studies of solid C10H8 in the region 450 to 130 cm—1, (b) studies of single crystals of C10H8 with polarized light in the spectral region 3500—450 cm—1 for the ab and bc planes at normal incidence, (c) study of gaseous C10H8 in the spectral region 1350—440 cm—1, (d) studies of single crystals of C10D8 with polarized light in the spectral region 3400—500 cm—1 for the ab plane at normal incidence, (e) study of a gaseous C10D8 in the spectral region 1000—700 cm—1. Most likely symmetry assignments for the absorptions of C10H8 and C10D8 are given and some of the bands of C10D8 are correlated with those of C10H8.
23(1955); http://dx.doi.org/10.1063/1.1741946View Description Hide Description
A critical examination of the oriented gas model is made on the basis of several suggested criteria applied to the infrared studies of solid C10H8 and C10D8. The frequency difference between gas and solidspectra is as high as 1 percent ν for only a few naphthalene bands. The dichroic band splittings which can be assigned to intermolecular interactions are small, averaging less than 3 cm—1, but with a few well defined exceptions. A comparison between the observed and predicted dichroic behaviors for those bands whose symmetry classes are known indicates that the dichroism is dominated by the gas phase symmetries of the vibrational modes. The general applicability of the oriented gas model for naphthalene indicates its usefulness in interpreting those solidspectra. On the other hand, the occasional, distinct deviations from the model warn that it is not likely to be useful in studying crystals involving stronger crystal forces (such as hydrogen bonds or ionic forces).
23(1955); http://dx.doi.org/10.1063/1.1741947View Description Hide Description
Infrared and Raman spectra taken of samples of naphthalene‐d‐8 of high deuterium content are reported. These spectra along with spectral data on naphthalene have been used to make an assignment of frequencies to the normal modes of vibration for this molecule. Although this assignment represents a significant contribution towards a correct one and provides good agreement with the experimental thermodynamic data, it still contains a number of tenuous points.
23(1955); http://dx.doi.org/10.1063/1.1741948View Description Hide Description
A complete vibrational assignment of naphthalene and naphthalene‐d 8 is presented. This assignment is in substantial agreement with the experimental thermodynamic properties, the product rule and the spectroscopic data. The assigned frequencies are used to calculate the thermodynamic properties of naphthalene, S 0, Cp 0, (H 0—E 0 0)/T, and — (F 0—E 0 0)/T from 273.16° to 1500°K.
23(1955); http://dx.doi.org/10.1063/1.1741949View Description Hide Description
The ΔJ=0, ΔF=0 transition in HCN and DCN in an excited bending mode of vibration was observed to possess structure due to an asymmetry in the electric field gradient at the nitrogen nucleus coupling to the quadrupole moment of that nucleus. A selective breaking of the π bond perpendicular to the plane of bending when the molecule assumes its ionic structure is suggested as the source of the asymmetry.
23(1955); http://dx.doi.org/10.1063/1.1741950View Description Hide Description
The quadrupole coupling of the deuteron (eqQ) D was measured in DCCCl where it was found to be +175±20 kc/sec. A less accurate determination of the absolute value (eqQ) D in DCN yielded approximately 290 kc/sec. The field gradient, q, at the deuterium nucleus in DCCCl is +8.85±10 percent×1014 esu. A calculation of q based on a Hund‐Mulliken molecular model yields a q of the same sign as that observed but approximately twice as large, indicating the insufficiency of the model for such detailed calculations.
23(1955); http://dx.doi.org/10.1063/1.1741951View Description Hide Description
The atomic polarizations,PA (theor.), of five diatomic molecules, HCl, DCl, HBr, NO, and CO, have been calculated from an equation derived from dispersion theory (Van Vleck, 1927), using recent data obtained from infrared dispersion and absorption intensity measurements. These PA (theor.) values are compared with the PA (exp.) values obtained from dielectric constant and optical refractive index measurements. The greater accuracy of the PA (theor.) values is emphasized. The PA (theor.) values have been used to recalculate the dipole moments, μ, of the diatomic molecules considered. A qualitative relationship is discussed between the series of dμ/dr and μ values for some of the diatomic molecules. The PA (theor.) are calculated approximately for the gaseous alkali halides.
23(1955); http://dx.doi.org/10.1063/1.1741952View Description Hide Description
The vacuum ultraviolet absorption spectra of bicycloheptane and bicycloheptene have been investigated in the region from 45 000 to 65 000 cm—1. Two distinct band systems with maxima at 51 125 and 59 715 cm—1 were noted in the case of bicycloheptene, each with an oscillator strength of 0.15. The first observed absorption of bicycloheptane was near 55 000 cm—1 while that of the unsaturated hydrocarbon was displaced more than 8000 cm—1 toward lower frequencies. In both compounds, sharp narrow bands were superimposed on the continuous absorption. In a study of the photodecomposition, it was shown that cyclopentadiene and ethylene were formed as photodecomposition products of bicycloheptane and also of bicycloheptene.
23(1955); http://dx.doi.org/10.1063/1.1741953View Description Hide Description
A vertical glass tube (1 cm bore and about 100 cm long) carries at its closed upper end two opposed spherical platinumelectrodes, approximately 1 and 2 mm in diameter. The lower end of the tube is bent upward in the form of a J, to which is attached a cylindrical reservoir. After introducing sufficient electrolyte (1NH2SO4) to more than fill the long tube, the system is evacuated and sealed off.
On rotating the long tube from an inverted to a vertical position, the column of liquid remains hanging from the top of the tube, under a negative pressure (at the top), equal to the length of the column down to the meniscus, times its density, less the vapor pressure in the reservoir. The minimumelectric charge required to drop the column is determined by successive trials, using a mica capacitor (adjustable in steps of 0.001 μf), which is first charged to a known potential and then connected to the electrodes through a quick‐acting switch. After each drop of the column, the polarity is reversed. Hydrogen is deposited as an incomplete monomolecular film when the smaller test electrode is the cathode; oxygen, when it is the anode.
The critical anodic charge was divided by 2, oxygen being bivalent. The ratio of the critical charges gives the relative number of molecules involved; and its reciprocal, the ratio of the projected areas. The mean of 9 series of measurements gave 1.022±0.006 as the ratio of the diameter of the oxygen to the hydrogen molecule. Measurements by other methods range from 1.54 to 0.89.
23(1955); http://dx.doi.org/10.1063/1.1741954View Description Hide Description
The radial distribution functions for binary mixtures of rigid spheres with a size ratio of 3 to 1 have been calculated at several mole fractions and at several densities by numerical solution of a set of integral equations obtained with the use of the superposition approximation. The distribution functions have then been used to evaluate the relevant thermodynamic properties of the system.
23(1955); http://dx.doi.org/10.1063/1.1741955View Description Hide Description
The density profile of the rarefaction wave which follows a detonation has been determined using the technique of x‐ray absorption measurements to follow rapid gas density changes. The observed density‐time dependence was found to agree, within experimental errors, with the predictions of the hydrodynamic theory developed by Taylor, Doering, and others. As the theory predicts, the density in the rarefaction wave decreases for approximately one‐half of the distance traveled by the detonation wave; behind this is the region of quiescent gas at constant density.
23(1955); http://dx.doi.org/10.1063/1.1741956View Description Hide Description
Measurements of the ac and dc response of illuminated F‐centered potassium bromide single crystals have been carried out. The dependence of crystal capacitance and conductance on frequency, light intensity, electrode character and separation, F‐center concentration, applied voltage, temperature, and optical bleaching time have been investigated. Most of the measurements were made on crystals containing both U and F centers, but a few were also made on additively colored and plain untreated crystals for comparison.
It was found that F centers in U‐centered crystals bleached much slower under strong illumination than did those in additively F‐centered crystals. The frequency response of the crystals depended significantly upon whether the electrodes were blocking or rectifying, but in both cases it was characterized by a single relaxation time given by the quotient of a series capacitanceC 0 and G ∞, the normal conductance of the crystal. C 0 was found to be independent of all variable parameters except dark storage and bleaching time and is thought to arise from a charge‐free layer located at one or both electrodes. Space‐charge capacitance effects were apparently largely hidden by C 0 but did probably produce a small voltage‐dependent non‐linearity observed at low frequencies with high applied voltages. G ∞, and thus the conduction‐band electron concentration, depended linearly on light intensity over a wide range but underwent a transition from linear dependence on F‐center concentration to independence thereof at high concentrations. Partly bleached crystals in total darkness exhibited appreciable conductivity, probably electronic in character. Most of the results on U‐centered crystals can be tentatively explained in terms of electron trapping by negative‐ion vacancies,F centers, interstitial hydrogen atoms, and hydrogen atoms in negative‐ion vacancies.
23(1955); http://dx.doi.org/10.1063/1.1741957View Description Hide Description
A theory of thermal diffusion in liquids has been developed based on Denbigh's interpretation of the ``net heat of transport'' which arises in the thermodynamics of irreversible processes. The thermal diffusion ratio α is expressed in terms of the energies of vaporization of the pure components, the excess energy, entropy and volume of mixing, and the concentration dependence of ΔU c. The efficiency with which the two species pack together is also introduced. The Hildebrand‐Scatchard solution theory is applied to these results and α is expressed in terms of solubility parameters, molal volumes and packing efficiencies.
The equations are compared with previously published experimental results, and reasonably explainable packing efficiencies are obtained.
In the appendices the effects of nonrandomness of mixing are considered and the theory is extended to ternary mixtures.
23(1955); http://dx.doi.org/10.1063/1.1741958View Description Hide Description
Simpson first called attention to the analogy between the free electron method in finite difference form and the simple LCAO molecular orbital method for electronic energy calculation. This analogy is extended to branched molecules using both the one‐ and two‐dimensional viewpoints and also applied to a case of two electrons in interaction. It appears that the success of the free electron method is due to this similarity to the LCAO method.
23(1955); http://dx.doi.org/10.1063/1.1741959View Description Hide Description
The thermal cis‐transisomerization of trans‐ethylene, d 2 has been studied from 450° to 550°C over a pressure range of 0.9 cm to 31 cm Hg in two quartz reactors. The rate is pressure dependent over the entire pressure range. It is concluded that at 0.9 cm the reaction is a homogeneous, unimolecular reaction. A high pressureactivation energy of 65 kcal and frequency factor of 1013 sec—1 are deduced. At higher pressures the reaction is sensitized by processes attendant on polymerization, which occurs as a side reaction with propylene as the principal product. The relation of this study to other work on substituted ethylenes is discussed briefly, as well as a few other topics pertinent to the results obtained.
23(1955); http://dx.doi.org/10.1063/1.1741960View Description Hide Description
The infrared spectrum of gaseous cyclobutforene has been obtained in the region from 2 to 38μ with the aid of LiF, NaCl, KBr, and KRS‐5 prisms. The Raman spectrum of the liquid phase has been photographed with a three‐prism glass spectrograph of linear dispersion 15 A/mm at 4358 A. With some uncertainties, especially as to symmetry species, all of the twenty‐four fundamental vibration frequencies have been assigned, and the spectra have been interpreted in detail.
23(1955); http://dx.doi.org/10.1063/1.1741961View Description Hide Description
The infrared spectrum of gaseous CF3CF2H has been observed in the region from 2 to 38μ, and the spectrum of the liquid at — 50°C from 2 to 22μ, with the aid of LiF, NaCl, KBr, and KRS‐5 prisms. The Raman spectrum of gaseous CF3CF2H has been photographed with a three‐prism glass spectrograph of linear dispersion 15 A/mm at 4358 A. All but one of the fundamental vibration frequencies have been assigned, and the spectra have been interpreted in detail.
23(1955); http://dx.doi.org/10.1063/1.1741962View Description Hide Description
The technique of temperature pattern determination, shown previously to be suitable for the measurement of fast gaseous reactions, has been extended to reactions of boron trifluoride with ammonia, dimethylamine, n‐butylamine, t‐butylamine, and pyridine. The bimolecular rate constants of the first two of these show pressure dependence; those of the other three, within experimental error, do not. A comparison with the previously obtained results on methylamine and trimethylamine demonstrates that the lifetime of the ``hot'' quasi‐molecules formed by the addition of boron trifluoride and an amine increases regularly with the number of vibrational degrees of freedom of the quasi molecule. The rates of addition are all substantially smaller than the rate of recombination of methyl radicals. They increase by about a factor of thirty from that of ammonia to those of heavier amines, being then about 1/30 of the collisional frequency. This finding is not consistent with the supposition that steric requirements alone limit the rates of addition and the existence of a small activation energy is clearly suggested, although it could not be observed experimentally. To explain the present results, the activation energy must decrease from ammonia to heavier amines. Such a decrease is found to be consistent with the presently accepted views on the electronic structure of the boron‐nitrogen bond.
23(1955); http://dx.doi.org/10.1063/1.1741963View Description Hide Description
The vaporizing species in the Al–Al2O3 system are identified mass spectrometrically. Intense ion currents of Al2O+ formed from gaseous Al2O are observed. At T = 1750°K ions formed from other gaseous oxides are at least 1000 times less intense than Al2O+. The appearance potential of Al2O+ is 7.7±0.2 ev. A thermodynamic treatment of gaseous Al2O gives for Al2O(g) = 2Al(g) + O(g), ΔH 298 = 256±7 kcal.