Index of content:
Volume 26, Issue 2, 01 February 1957
Spectroscopic Survey of Energy Distributions of OH, C2, and CH Radicals in Low Pressure Acetylene‐Oxygen Flames26(1957); http://dx.doi.org/10.1063/1.1743273View Description Hide Description
Rotational and vibrational ``temperatures'' from electronic transitions of OH, C2, and CH radicals have been measured in detail as functions of position in low pressure acetylene‐oxygen flames.Pressures were varied from 0.8 to 6.0 mm Hg. Trends of ``temperature'' are presented as functions of mixture, pressure, position, mass flow rate, and burner size. Abnormalities in ``temperature'' are discussed. Evidence is presented for the existence of a newly discovered region at the base of the flame. This region is about the visible flame thickness and is characterized by strong emission of C2 and CH relative to OH and by relatively high ``temperatures'' of C2 and CH. Just above this region the OH rotational ``temperature'' is very high, about 9000°K, and is independent of pressure.
26(1957); http://dx.doi.org/10.1063/1.1743274View Description Hide Description
The heat capacity of α‐quartz has been computed over the temperature range 10–700°K, and that of vitreous silica from 10° to 900°K. Debye θ's obtained from the T 3 law below 10° were used for the ``translational'' degrees of freedom, and recent infrared and Raman data for the other frequencies. Cp —Cv was negligible for vitreous silica and was computed from compressibility and thermal‐expansion data for α‐quartz. Agreement with new Cp measurements is excellent for α‐quartz (within 1% above 60°K) but is less satisfactory for vitreous silica because of inadequate knowledge of the distribution of frequencies below 500 cm—1.
Vibrational Spectra, Potential Constants, and Calculated Thermodynamic Properties of cis‐ and trans‐BrHC=CHBr, and cis‐ and trans‐BrDC=CDBr26(1957); http://dx.doi.org/10.1063/1.1743275View Description Hide Description
Raman displacements for the liquid and infrared absorption wave numbers for both liquid and gas, together with quantitative depolarization factors for the Raman lines and semiquantitative relative intensities for both Raman and infrared bands, have been obtained for cis‐ and trans‐BrHC=CHBr and cis‐ and trans‐BrDC=CDBr. Assignments, consistent with the selection rules, were made for the 4 molecules. As a further check on the assignments a normal coordinate treatment (Wilson FGmatrix method) was carried out. The heat content, free energy,entropy, and heat capacity for each of the molecules were calculated for 12 temperatures from 100 to 1000°K for the ideal gaseous state at 1 atmos pressure. Finally the energy difference between the cis‐ and trans‐isomers of C2H2Br2 has been calculated.
26(1957); http://dx.doi.org/10.1063/1.1743276View Description Hide Description
The microwave spectrum of the symmetric tops, CF3C≡C–CH3 and CF3C≡C–CD3, has been investigated. Excited vibrational state transitions were observed, but the l‐type doublet fine structure was not resolvable. Since lines originating from species containing C13 in natural abundance were identified, only two assumptions were necessary in order to determine the 7 structural parameters. The parameters giving the best fit with the experimental data are: d(C,F) = 1.340, d(C(1), C(2)) = 1.455 = d(C(3), C(4)), d(C(2), C(3)) = 1.189, and d(C,H) = 1.097 A and the angles ∠F–C–F = 106°08′ and ∠H–C–H = 108°30′.
26(1957); http://dx.doi.org/10.1063/1.1743278View Description Hide Description
The specific heat of heavily irradiated Acheson‐type graphite has been measured from 13° to 300°K. Throughout this temperature range, the specific heat of the irradiated graphite is appreciably larger than that of unirradiated graphite of similar type. This difference is explained by assuming that interplanar atoms or clusters of atoms, give rise to modes of low energy which contribute to the specific heat at lower temperatures than do the normal lattice modes. The entropy of the irradiated sample at 298.16°K is 1.492±0.009 cal/g‐atom deg compared with 1.372±0.005 cal/g‐atom deg for the unirradiated graphite.
26(1957); http://dx.doi.org/10.1063/1.1743279View Description Hide Description
The infrared absorption spectra of urea, thiourea, and thiourea complexes with cesium bromide, potassium iodide, potassium bromide, sodium bromide, and sodium iodide have been observed from 2 to 40 μ, except for the sodium iodide complex which was studied between 2 and 15 μ. The vibrations of urea and thiourea are assigned on the basis of a planar C 2v structure.
26(1957); http://dx.doi.org/10.1063/1.1743280View Description Hide Description
Observations are reported on the polarized infrared spectra of single crystals of urea and thiourea in the 3μ region. Complex structures accompanying the N – H fundamentals appear, at least in considerable part, to be attributable to combinations and overtones of fundamentals in the neighborhood of 1650 cm—1.
26(1957); http://dx.doi.org/10.1063/1.1743281View Description Hide Description
Absorption spectra of rubidium in the presence of fourteen different hydrocarbons (methane, ethane, propane,n‐butane, n‐pentane, n‐hexane, n‐heptane, n‐octane, n‐nonane, n‐decane, n‐dodecane, cyclopropane, butene‐2, and benzene) were studied. About one hundred new rubidium‐hydrocarbon absorption bands associated with the first four members of the Rb principal series were observed. Some regularities in the occurrance of the bands were found. The positions of the bands are given and the properties of the bands are discussed.
Calculation of Compressibilities of High Polymers from the Energy of Interaction between Chain Groups26(1957); http://dx.doi.org/10.1063/1.1743282View Description Hide Description
A potential function for the interaction of long chain molecules in polymer lattices is formulated. The adopted model assumes polymeric substances to consist of imperfect assemblies of perfect chain crystals. The chains are infinitely long compared to the range of intermolecular forces so that end effects can be neglected. Each chain is composed of evenly spaced dipolar dispersion force centers, with dipole orientations perpendicular to and alternating along the chain axes. Pairs of force centers in neighboring chains interact according to a Lennard‐Jones (12–6) potential and the electrostatic interaction terms. The interaction between neighboring force centers within a chain is assumed to be Hookian with a force constant calculated from combined valence bond distortions and valence angle deformations.
The lattice energies of five linear polymers are calculated. It is found that the contributions from induction terms are negligible. The contributions from dipole interaction terms depend on the mutual orientation of the chains and amount to only ca 0.1–1% of the lattice energies. To this accuracy, certain ``structure insensitive'' properties can be described by an equation of corresponding intermolecular states. This approach is shown to fail, if applied to ``structure sensitive'' properties, which depend strongly on the interplay of inter‐ and intramolecular degrees of freedom. Absolute calculations of specific polymer volumes over large pressure ranges are in agreement with experiment.
26(1957); http://dx.doi.org/10.1063/1.1743283View Description Hide Description
In chemical kinetics it is customary to determine the concentrations of each of the free radicals and chemically unstable intermediates by assuming that these intermediates are in pseudostationary equilibrium with the principal chemical components. The mathematical nature of the pseudostationary approximation is examined and a method is developed for testing its validity or improving its accuracy in specific cases. In those cases where the rates of destruction of the intermediate compounds are rapid, the pseudo‐stationary solutions are accurate.
26(1957); http://dx.doi.org/10.1063/1.1743284View Description Hide Description
If a chemically reacting mixture is confined between two parallel plates, one hot and the other cold, the temperature and the chemical composition at a point, as well as the over‐all heat flux, depend upon the rates of both the homogeneous reactions in the gas phase and the heterogeneous reactions on the surfaces. However, if the reaction rates are fast in either the forward or the reverse direction, the assumption of local chemical equilibrium (which is equivalent to the thermodynamics of irreversible processes) is found to be very good. Under such conditions the heat conductivity behaves as though the reacting gas mixture were a pure substance with an effective coefficient of thermal conductivity. A simple equation is given for this effective coefficient of thermal conductivity. Detailed examples are given for a unimolecular rearrangement A⇄B and for the dissociation of oxygen, 02⇄20. The analysis applies equally well to liquid and to gaseous mixtures.
26(1957); http://dx.doi.org/10.1063/1.1743285View Description Hide Description
The usual Eucken equation for the heat conductivity of a molecule with internal degrees of freedom is derived and improved. In the improved form the correction to the coefficient of thermal conductivity for the internal degrees of freedom of the molecule is given by the factor 0.115+0.354 Cp/R. With the help of Part I, we prove that this approximation is valid only if the electronic states are not metastable and if the coefficients of diffusion of all the molecular quantum states are equal. The metastable electronic species should lead to anomalously large coefficients of thermal conductivity, whereas the usual excited electronic states, because of their gigantic size, should give a much smaller contribution to the coefficient of thermal conductivity than would be expected on the basis of the Eucken assumption.
26(1957); http://dx.doi.org/10.1063/1.1743286View Description Hide Description
While there are many experimental measurements on binary liquid systems, very few measurements have been designed specifically for statistical mechanical analysis. This paper describes an effort to design a series of experiments to secure all necessary information for theoreticalanalysis. The necessary measurements are those of vapor pressure, heats of mixing, variation of density with composition, and measurements of the viscosities of mixed vapors. This system of experiments is used on the system perfluoroheptane and iso‐octane. The analysis of the data is discussed and calculations of the thermodynamic properties and intermolecular potential are carried out.
26(1957); http://dx.doi.org/10.1063/1.1743287View Description Hide Description
Using the TFD electron density, recently published by one of us (T), the atomic scattering factor f 0 has been calculated for neutral atoms as well as for singly through quadruply ionized positive ions with intermediate atomic numbers on the IBM 607 and 650. The f 0 values thus obtained for Ar and Cu+ agree qualitatively with those calculated from the Hartree‐Fock fields recently by MacGillavry et al. The experimental fact has been again confirmed, that the f 0 value is not much influenced by the state of ionization. The effect of exchange has been displayed by the deviation of the TFD curve of the atomic scattering factor per electron versus the Bethe variable ξ, from the TF universal curve. The TFD curve of versus Z for a definite state of ionization has a slight minimum at a certain value of Z which increases with decreasing scattering angle and tends finally at vanishing scattering angle to a definite limiting value just corresponding to the maximum of 〈r 2〉Av.
26(1957); http://dx.doi.org/10.1063/1.1743288View Description Hide Description
Mass spectra and appearance potentials are presented for the principal positive and negative ions of hexafluorobenzene along with comparative data for benzene. Although complete analysis of bond dissociation energies is prevented by lack of thermochemical data, the C–F bond is estimated to be 145 kcal. Qualitatively, the results indicate that C6F6 is thermally more stable than C6H6 and is a relatively stable configuration in the presence of ionizing radiation.
26(1957); http://dx.doi.org/10.1063/1.1743289View Description Hide Description
The molecular beam method for the measurement of the lifetime of metastable states has been improved by the introduction of differential pumping, control of the energy of the bombarding electrons, and use of a movable detector.
A lower limit of 10—2 sec is obtained for the lifetime of the A 3Σ u + state of N2, in closer agreement with spectroscopic observations than the previous work of Muschlitz and Goodman.
The measured value of the lifetime of the a 1II g state of N 2 is (1.7±0.3)×10—4 sec.
Some new observations on metastable states of the rare gas atoms, A, Kr, and Xe; CO and H2 are mentioned briefly.
26(1957); http://dx.doi.org/10.1063/1.1743290View Description Hide Description
A number of new metastable transitions have been identified in the mass spectra of n‐butane and i‐butane. The appearance of various metastable transitions was discussed in terms of the quasi‐equilibrium theory of mass spectra and the energetics of ionic decomposition processes. A study of the pressure independence of metastable transitions revealed the existence of several collision‐induced dissociations. Some similarities of these processes to electron impact‐induced dissociations were pointed out. Approximate relative cross sections were determined for the various collision processes.
26(1957); http://dx.doi.org/10.1063/1.1743291View Description Hide Description
The importance of energy transfer by collision (used in the sense of diffusion together of an excited and an unexcited molecule) has been investigated by measuring the fluorescence of nearly identical solid and liquidsolutions under like conditions. Since the solids seem to transfer as well as the liquids, the conclusion is made that the ``collision'' mechanism does not play a major part in this type of transfer.
26(1957); http://dx.doi.org/10.1063/1.1743292View Description Hide Description
A general method is described for evaluating the third virial coefficient for any intermolecular potential in which the interaction varies as a sum of inverse powers of the distance outside a hard‐sphere core. The calculations involve only simple algebraic operations and can be extended to include angular dependent potentials, quantum effects, and mixtures of molecules. An illustrative calculation on a modified Lennard‐Jones potential shows the dependence of the third virial coefficient on the repulsive forces.
26(1957); http://dx.doi.org/10.1063/1.1743293View Description Hide Description
The infrared and Raman frequencies of liquid VOCl3 (of symmetry C 3v ) have been measured. The a 1 fundamentals are 1035, 408, and 165 cm—1; those of species e are 504, 249, and 129 cm—1. Most of the fifteen remaining bands can be explained as combinations of these.