Index of content:
Volume 21, Issue 10, 01 October 1953
21(1953); http://dx.doi.org/10.1063/1.1698633View Description Hide Description
The very strong 1560‐cm−1 band of the N‐substituted amide group has been assigned previously either to ν(C–N) or to δ(N–H). This investigation consisted of a study of the frequency shifts of this and other bands in the infrared spectra of several N‐butyl‐ and N,N‐dibutyl‐ethanamides upon substitution of chlorine and fluorine in the 2 position. On the basis of these shifts and other properties of the band in question, observed in the spectra both of the pure compounds and of their CCl4 solutions, it is concluded that the ν(C–N) assignment is correct. The apparent absence of the corresponding band from the spectrum of the N,N‐disubstituted amide group is explained by the accidental degeneracy of ν(C=O) and ν(C–N). Other bands were cataloged and assigned where possible.
21(1953); http://dx.doi.org/10.1063/1.1698634View Description Hide Description
The volume exclusion effect in a chain of small impenetrable spheres is treated by two methods—one based on derivation of a Fokker‐Planck equation by consideration of the number of ways in which a chain can be extended by adding another sphere without violating the volume exclusion condition, and the other based on the calculation of the number of excluded configurations as a function of chain extension. Both approaches lead, in the first approximation, to the same simple analytic form for the distribution of chain extensions r, and to the prediction that 〈r 2〉 will increase faster than the number of spheres in the chain. Volume exclusion does not merely change the distribution function by a scale factor, as is assumed in the theory of Flory; there is a relatively large decrease in the probability of small extensions. The present theory is compared in detail with that of Hermans, Klamkin, and Ullman, which is superficially similar in appearance, but fundamentally quite different in character and result.
21(1953); http://dx.doi.org/10.1063/1.1698635View Description Hide Description
The recombination rate constant of methyl radicals has been redetermined by the intermittent illumination method as 3.7×1013 cc/mole sec at 165°, after a correction for the concurrent formation of methane. The recombination rate constant of deuterated methyl radicals has been found to have a substantially identical value. The dependence of these second‐order rate constants on total pressure was studied over the range of 1‐ to 10‐mm acetone pressure. Both rate constants were found to decrease identically with pressure. The form of their pressure dependence agrees with deductions from the ``third‐body'' stabilization theory. It is shown that the absolute magnitude of the recombination rate constants, their near‐identity and their identical decrease with pressure are all consistent with theoretical predictions, provided the methyl radicals form a loosely bound critical complex, in which they carry out essentially unhindered rotations. Recent literature data on the recombination of methyl radicals are reviewed, and it is shown that they are not in serious disagreement with the present measurements.
21(1953); http://dx.doi.org/10.1063/1.1698636View Description Hide Description
Absorption coefficients of N2O in the region 1080–2100A have been measured. Four continua were observed with maxima at 1820, 1450, 1285, and 1080A having f values of 0.0015, 0.0211, 0.367, and 0.1, respectively. The strongest absorption band in the ultraviolet lies at 1178A with an absorption coefficient of 3010 cm−1 at its maximum. A number of new bands were observed, and some of them classified. Some of the continua have been interpreted in terms of possible dissociation processes, and a potential energy diagram is presented.
21(1953); http://dx.doi.org/10.1063/1.1698637View Description Hide Description
Quantitative absorption coefficient measurements have been made for CO2 in the region 1050–1800A using a 1‐meter vacuum monochromator with a phosphor‐coated photomultiplier tube as detector. The absorption spectra obtained consisted of three continua (λmax at 1121, 1332, 1475A) and possibly a fourth, all being superposed by many bands. For each continuum f values have been calculated. The results have been compared with some theoretical formulations by Mulliken. Upper limits of dissociation energies of the excited states of CO2 are estimated.
21(1953); http://dx.doi.org/10.1063/1.1698638View Description Hide Description
Absorption coefficients of ozone gas (purity 90–95 percent) were obtained in the region 1050–2200A by a method described previously. Several strong continua, as well as weak bands, were observed. The curve for absorption intensity shows a minimum (8 cm−1) at about 2015A. Below this wavelength, the absorption coefficient increases gradually to a weak maximum (23 cm−1) at about 1725A and then rapidly to a strong maximum (420 cm−1) at about 1330A. In the region 1050–1450A, the absorption intensity does not fall below the value 130 cm−1. The results were compared with Mulliken's treatment of the electronic spectrum of ozone.
21(1953); http://dx.doi.org/10.1063/1.1698639View Description Hide Description
Further studies in the ultraviolet region between 4000 and 2500A indicate that the magnitude of the photopotential derived from a photoactive substance in solution is dependent on the absorption of the solution. Aliphatic and aromatic alcohols, hydroxy acids and phenols produce practically no photopotentials between 3000 and 8000A. The photovoltaic behavior of 38 organic halides has been studied. Methyl iodide produced the highest photopotential of any of the compounds used. The normal halides other than the iodides were inactive. In general the iso, secondary, and tertiary halides were more active than the corresponding normal halides. Results on 89 compounds other than halides are listed.
21(1953); http://dx.doi.org/10.1063/1.1698640View Description Hide Description
The specific heat of high‐purity Acheson graphite prepared by the National Carbon Company has been measured from 13° to 300°K. In the region 13° to 54°K the Cp data follows a T 2 dependence quite accurately in agreement with previous experimental work and recent theoretical investigations of specific heat in strongly anisotropic solids.
On the basis of some recent studies for other highly anisotropic solids, it is suggested that the specific heat of graphite will eventually follow a T 3 dependence at still lower temperatures.
The derived thermodynamic functions,entropy,enthalpy, and free energy, have been determined by graphical integration and tabulated at integral values of temperature up to 300°K. The entropy of graphite at 298.16°K is 1.372±0.005 cal/g‐atom deg, of which 0.004 is extrapolated from 13° to 0°K assuming the third law and the T 2 dependence.
21(1953); http://dx.doi.org/10.1063/1.1698641View Description Hide Description
Recent experiments have shown that the specific heat of graphite varies as T 2 instead of T 3 between 15°K and 80°K. In this paper such a behavior is shown to be a consequence of the elasticanisotropy of graphite, and therefore an intrinsic property, rather than a particle size effect as suggested by Gurney, or a plate‐like behavior as suggested by Komatsu and Nagamiya. The Gurney treatment is shown to be in error both as to the enumeration of modes, and as to the temperature range over which the particle size effect might be of significance. The Komatsu and Nagamiya treatment is shown to be inconsistent with elasticity theory. The present treatment employs a semirigorous analysis of the normal mode problem for the transverse vibrations, approximated for long wavelengths. It is found that experimental data from 15–1000°K can be well fitted by dividing the lattice vibrations into two types: (a) modes with atom displacements normal to the layer planes with a Debye temperature of 900°K, and (b) modes with atom displacements in the planes with a Debye temperature of 2500°K.
21(1953); http://dx.doi.org/10.1063/1.1698642View Description Hide Description
A theory was developed for computing the probability of transition, upon molecular collision, between vibrational states, involving corresponding conversion of translational energy. A spherically symmetric Lennard‐Jones 6–12 potential for interaction between the colliding molecules was introduced; their relative translational motion was described classically. Further, the theory was symmetrized to permit inclusion of collisions with nonzero impact parameters. As an example, the theory was applied to the CO2–H2O system. The effective collision diameter for an inelastic event was found to be of the observed order of magnitude, demonstrating not only the selective relaxation effect of water, but also its somewhat unusual temperature dependence.
Zener's solution of the problem for a head‐on collision was generalized to three‐dimensional collisions, assuming a spherically symmetric interaction potential; but the complete solution of this model, including a quantum‐mechanical description of the relative translational motion, was not obtained. However, for such a potential it was possible to demonstrate that the semiclassical theory is an adequate approximation to the quantum theory result, whenever the relative translational energies are much greater than the energy of exchange.
21(1953); http://dx.doi.org/10.1063/1.1698643View Description Hide Description
21(1953); http://dx.doi.org/10.1063/1.1698644View Description Hide Description
The position of the protonmagnetic resonance is concentration dependent in aqueous solutions of electrolytes yielding hydrogen containing ions. Chemical exchange averages the chemical shifts in the protonresonance position over the different chemical species. The averaged shifts observed are correlated with dissociation of the solute, and evidence is obtained in very concentrated solutions for the incomplete dissociation of HNO3, HClO4, and H2SO4 and for the formation of ion pairs of Na+OH−. A theoretical analysis of the relation between the magnetic absorption line shape and the chemical exchange frequency suggests that rather short chemical lifetimes can be measured; at least one can infer from the appearance of a single or complex resonance that the average lifetime is greater or less, respectively, than a determinable value in a range about 10−2 to 10−4 sec.
21(1953); http://dx.doi.org/10.1063/1.1698645View Description Hide Description
Measurements have been made of the protonmagnetic resonance absorption in methyl chloroform, 2,2‐dinitropropane, 2‐chloro−2‐nitropropane, t‐butyl chloride, t‐butyl bromide, and neopentane, in the solid state. In all the materials at −196°C, except neopentane, the absorption corresponds to CH3 groups effectively fixed in the lattice. The narrowing of the absorption lines with rising temperature in methyl chloroform, 2,2‐dinitropropane, and 2‐chloro−2‐nitropropane is attributable to the increasing rate of motion of the CH3 groups about their C 3 symmetry axis. In methyl chloroform at higher temperatures, and in t‐butyl chloride, t‐butyl bromide, and neopentane an additional motion of the CH3 groups is required to explain the observed absorption, and possible motions are suggested. In all the polar materials the line becomes very narrow at the thermal transition at which the dielectric constant rises to a high value, marking the onset of over‐all molecular rotation. In neopentane the line is narrower than expected for the rigid lattice at −196°C. With rising temperature, the line narrows to a very small value between the thermal transition and melting points. Theoreticalanalyses are given of the effects of external broadening upon the line shapes of fixed and rotating CH3 systems, and the results are used in interpreting the experimental data.
Proton Magnetic Resonance of the CH3 Group. II. Solid Solutions of t‐Butyl Chloride in Carbon Tetrachloride21(1953); http://dx.doi.org/10.1063/1.1698646View Description Hide Description
Measurements of the protonmagnetic resonance absorption in solid solutions of t‐butyl chloride in carbon tetrachloride are reported for temperatures above −195°C. The results confirm, in general, the phase diagram established previously by thermal and dielectricmeasurements. In addition, information is obtained on the CH3 group and molecular motions in the various phases. Rotation of the CH3 groups at −195°C depends on the composition. In solutions between 34.9 and 70.6 mole percent t‐butyl chloride there is effective rotation of the CH3 groups about their C 3 axes whereas in pure t‐butyl chloride the CH3 groups are fixed at this temperature. For some compositions two separate phases are formed at low temperatures and the observed absorption agrees with that predicted from the properties and relative proportions of the protons in the two phases. Somewhat anomalous results were obtained for the more dilute solutions. For all compositions at temperatures above −150°C the resonance line narrows to about the same value, 3 gauss, and this is shown to be due to rotation of the molecule about the C–Cl bond in addition to rotation of the CH3 groups about their C 3 axes. Other possible motions are discussed, and the second moment of the absorption line is calculated theoretically for complex motions of the CH3 group. The differences in the freedom of motion of the CH3 groups in the different phases are attributed to interactions both within a molecule and with neighboring molecules.
21(1953); http://dx.doi.org/10.1063/1.1698647View Description Hide Description
From measurements of pure rotational transitions in the microwave region, the following molecular constants have been obtained. The B 0 values are in Mc/sec, 2472.45±0.04 for HSi28Cl3 35; 2346.07±0.04 for HSi28Cl3 37; 1769.84±0.03 for C12H3SI28Cl3 35; 1699.79±0.03 for C12H3Si28Cl3 37; 2197.44±0.04 for (C12H3)3Si28Cl35; and 2147.88±0.03 for (C12H3)3Si28Cl37. With d SiH=1.47A (assumed), it is found for SiHCl3 that d SiCl=2.021A and ∠ClSiCl=109°22′. With the CH3 configuration assumed as in methane and ∠ClSiCl as in SiHCl3 it is found for CH3SiCl3 that d SiC=1.876A and d SiCl=2.021A. With all bond angles assumed to be tetrahedral and the CH distance to be that in methane, it is found for (CH3)3SiCl that dSiC=1.87A and d SiCl=2.03A.
21(1953); http://dx.doi.org/10.1063/1.1698649View Description Hide Description
From measurements of the pure rotational transitions in trichloro germane, the rotational constantsB 0 (in megacycles/sec) for the various isotopic modifications of the molecule were found to be: 2172.75 for HGe70Cl3 35, 2169.26 for HGe72Cl3 35, 2165.84 for HGe74Cl3 35, 2063.74 for HGe70Cl3 37, 2060.43 for HGe72Cl3 37, and 2057.20 for HGe74Cl3 37. The calculated structure from the above data for the molecule in the ground state is: d GeH=1.55±0.04A, d GeCl=2.1139±0.0010A, and ∠ClGeCl=108°17′±12′. Rotational lines for the molecule when it is in the two excited GeCl3 deformation vibrations are also measured and the corresponding molecular structures calculated.
21(1953); http://dx.doi.org/10.1063/1.1698650View Description Hide Description
This discussion is concerned with the excluded volume effect in polymer chains, i.e., the mathematical problem of random flights with correlations between the flights, which is of importance in relating the mean size of a chain to its structure. A general formulation of the problem is set up and compared with the theory of Markoff processes. It is shown that although an integral equation of the Markoff form for the distribution function exists, it contains a complicated function whose exact evaluation is difficult. Since the same function occurs in the problem of the osmotic second virial coefficient, it is natural to relate the excluded volume effect to the second virial coefficient. The results of preliminary numerical calculations for the relation between the mean square radius of the chain and the second virial coefficient, in good agreement with experiment, are given. It is concluded that the volume effect is certainly not negligible for real chains, except when the second virial coefficient is zero, and that the effect increases with increasing chain length.
21(1953); http://dx.doi.org/10.1063/1.1698651View Description Hide Description
Mercury dimethyl was photolyzed in the presence of various hydrocarbons between 28°C and 251°C. The activation energies in kcal per mole for reactions of the typeare: 2‐methyl propane−7.4; 2,3‐dimethyl butane−6.8; n‐butane−8.6; cylcohexane−8.3; 2,2‐dimethyl propane−10.4; and toluene−7.3, where it is assumed that the activation energy for the reactionis zero. The collision theory steric factors are less than 10−3 for all these reactions.
The agreement of the above results with those obtained from the photolysis of acetone is noted.
21(1953); http://dx.doi.org/10.1063/1.1698652View Description Hide Description
The infrared absorptionspectrum of liquid 1,2,4‐trifluorobenzene has been obtained in the region 2–38μ with the aid of LiF, NaCl, KBr, and KRS−5 prisms. The Raman spectrum of the liquidh as been photographed with a three‐prism glass spectrograph of linear dispersion 15A/mm at 4358A, and depolarization ratios have been measured for the stronger Raman bands. A complete assignment of fundamental vibration frequencies is given, and the spectra are interpreted in detail.
21(1953); http://dx.doi.org/10.1063/1.1698653View Description Hide Description
The infrared absorption of liquid 1,4‐bis(trifluoromethyl) benzene has been obtained in the region 2–22μ with the aid of LiF, NaCl, and KBr prisms. The Raman spectrum has been photographed with a three‐prism glass spectrograph of linear dispersion 15A/mm at 4358A. A nearly complete assignment of fundamental vibration frequencies is given, and the spectra are interpreted in detail.