Volume 22, Issue 2, 01 February 1954
Index of content:
22(1954); http://dx.doi.org/10.1063/1.1740023View Description Hide Description
The total vapor pressure of graphite is calculated as a function of temperature to the harmonic oscillator‐rigid rotator approximation. It is assumed that three species (C1, C2, and C3) are present in the gas. The C1 atoms are most prominent in the mixture. C3 molecules are relatively more abundant than C2 diatoms. The heats of sublimation of the various carbon species are discussed.
22(1954); http://dx.doi.org/10.1063/1.1740024View Description Hide Description
Chemical shifts in the phosphorus nuclear magnetic resonance absorption have been measured in twenty compounds. The shifts arise from differences in the magnetic shielding of the phosphorus nuclei by electrons, and the values observed are interpreted qualitatively in terms of the molecular electronic structures. The range in shifts in 7×10—4 which is somewhat larger than observed for fluorine on which more extensive data are available. The phosphorus resonance shifts fall into two distinct groups one of which contains compounds with trivalent phosphorus and the other, pentavalent. The shifts in pentavalent compounds fall in a relatively narrow range, generally with greater nuclear magnetic shielding than in the trivalent. The resonance shifts between similar or homologous compounds can be accounted for by considering changes in the importance of ionic and double‐bonded electronic structures.
22(1954); http://dx.doi.org/10.1063/1.1740025View Description Hide Description
The specific reaction rate for chemical reactions is formulated in terms of the totaltransmission coefficient in the reaction coordinate and a modified transition state, which differs from the original transition state only in the treatment of the reaction coordinate. If the total transmission coefficient is factored into two partial transmission coefficients, the modified theory gives the transition state theory in both the classical and the quantum‐mechanical‐particle‐in‐a‐box treatments. It is then shown that the momentum density in the virtual state over a symmetrical square barrier is that of a quantum‐mechanical‐particle‐in‐a‐box at low momentum and that of a classical system at high momentum. Finally, the reaction rate transmission coefficient is calculated from the modified theory for an unsymmetric square barrier and shown to depend on the temperature, the activation energy, and the thermicity of the reaction.
22(1954); http://dx.doi.org/10.1063/1.1740026View Description Hide Description
A large number of the Chapman and Cowling collision integrals have been calculated for gases obeying a modified Buckingham potential,The results are tabulated over a large temperature range, kT / ε from 0 to 200, and for four values of the parameter α, 12, 13, 14, and 15. The treatment was entirely classical, and no corrections for quantum effects were made. The results should be applicable to most simple, nonpolar gases, and may be used to obtain information about intermolecular forces from the observed temperature dependence of gaseous transport properties.
The second approximation to the thermal diffusion ratio and the third approximation to the coefficient of ordinary diffusion have been derived according to the method of Chapman and Cowling.
Evaluation of the potential parameters for specific substances and applications of the results will be published later.
22(1954); http://dx.doi.org/10.1063/1.1740027View Description Hide Description
The second virial coefficient has been calculated for gases obeying a modified Buckingham potential, (Exp‐Six),The results are tabulated over the temperature range kT / ε from 0.40 to 400, and for seven values of the parameter α, from 12 to 15. The treatment was entirely classical, and no corrections for quantum effects were made.
A separate paper will present the evaluation of the parameters for specific substances and applications of the results, together with applications of the calculated transport properties given in the preceding paper.
22(1954); http://dx.doi.org/10.1063/1.1740028View Description Hide Description
Raman (liquid) and infrared (liquid and gas, with KBr and NaCl prisms)spectra have been obtained for two mixtures of C13H3I (9.3 and 61 atom percent) and C12H3I, and from these the vibrational spectrum of C13H3I has been deduced. In the Raman spectrum, only v 3(a 1)—the C–I stretching frequency—could be resolved from the C12H3I lines; the isotopic shift was — 17.7±0.5 cm—1. In the infrared spectrum (gas), five isotopic shifts were obtained; they were: v 1(a 1) — 10±3, v 2(a 1) — 5.5±1.0, v 3(a 1) — 16.1±1.0, v 5(e) — 4.4±0.8, and v 6(e) — 3.7±0.3 cm—1. For the remaining fundamental, v 4(e), the shift was obtained by use of the Redlich‐Teller product rule; the value was — 9.4±2.3 cm—1. Analysis of the perpendicular bands yielded, with the aid of microwave data, values of the rotational constants, Coriolis interaction constants, and band origins for the v 6(e), v 5(e), and v 4(e) bands of C12H3I and C13H3I, though the values for the v 4(e) band of C13H3I are incomplete and are only estimated values since the sub‐bands were not resolved in this case.
22(1954); http://dx.doi.org/10.1063/1.1740029View Description Hide Description
The energy difference between the rotational isomers of the gauche‐ and trans‐forms of 1,2‐dichloroethane in various solutions have been calculated by use of a modified Onsager's reaction field. The following assumptions have been employed in the calculation: first, the cavity of the solute molecule is spheroidal; second, the dipole moment of the molecule is composed of two point dipoles which are placed at the foci of the spheroidal cavity, the focal distance being taken as equal to the distance between the contact points of the carbon and chlorine atoms in the dichloroethane molecule. The change of energy difference between rotational isomers by solvents thus computed has been found to be in close agreement with the experimental observations, that is, those obtained by infrared absorption measurements as well as dipole moment.
22(1954); http://dx.doi.org/10.1063/1.1740030View Description Hide Description
The infrared spectra of thin films of H2NOH and D2NOD were obtained at — 78° and — 190°C in the region 4000—500 cm—1. Two distinct types of spectra resulted depending on whether the films were formed at — 78° or at — 190°C. The spectra obtained when the films were formed at — 190°C were characterized by broad overlapping bands; those formed at — 78°C gave much narrower bands, some of them splitting into two or more distinct components. The latter type spectrum is representative of the stable crystalline form at low temperature. This spectrum could not be correlated with the amine oxide form of hydroxylamine, NH3→O. Satisfactory vibrational assignments could, however, be made for the model with symmetry of the point group C 3, H2NOH. If cis‐ and trans‐rotational isomers coexist in the solid, they must possess very nearly the same potential energy or at least a high potential barrier between them. The O–H stretching vibration in the solid is found at a very low frequency, 2867 cm—1, indicating a very strong hydrogen‐type bond with energy of about 13 kcal per mole.
22(1954); http://dx.doi.org/10.1063/1.1740031View Description Hide Description
A description is given of the method used to measure the dielectric constant of steam at densities between 0.2 and 0.4 g/cc in the temperature range 377 to 395°C. Smoothed values of the dielectric constant are tabulated at 378, 383, 388, and 393°C for densities from 0.1 to 0.5 g/cc.
22(1954); http://dx.doi.org/10.1063/1.1740032View Description Hide Description
A description is given of the method used to measure the electrical conductivity of NaCl in steam at steam densities between 0.2 and 0.4 g/cc. Values of the specific and equivalent conductances are tabulated at 378, 383, 388, and 393°C for various NaCl concentrations at different steam densities. Sodium chloride behaves as a weak electrolyte at all steam densities used. Estimates of the ion‐pair dissociation constant K, based on Shedlovsky's method, indicate that K decreases from about 9×10—3 to 6×10—7 as the steam density decreases from 0.4 to 0.2 g/cc. Preliminary results for cesium chloride and hydrogen chloride in steam indicate that cesium chloride is comparable in strength with sodium chloride, but that hydrogen chloride is a much weaker electrolyte.
The Infrared Spectra and Structure of LiOH, LiOH·H2O and the Deuterium Species. Remark on Fundamental Frequency of OH‐22(1954); http://dx.doi.org/10.1063/1.1740033View Description Hide Description
The infrared spectrum of a thin path of solid LiOH and LiOH·H2O (undeuterated, partially deuterated, and completely deuterated) has been observed. The spectra indicate that both hydrogens from each water molecule are used to form strong hydrogen bonds in the hydrate. The results serve to substantiate the crystal structures previously determined by x‐ray diffraction. For LiOH the absorption maximum occurs at 3678±1 cm‐1; the fundamental frequency of OH‐ in LiOH is 3839±10 cm‐1. The spectrum of LiOH·HDO exhibits an anomaly in the bending frequency of HDO.
22(1954); http://dx.doi.org/10.1063/1.1740034View Description Hide Description
Single crystals of PbSe were grown from melts in sealed quartz tubes. Except for a very narrow range of initial melt compositions, stoichiometric excesses of Pb or Se in the melt resulted in crystals that were wholly n or p type, respectively. Initial composition within the critical range yielded crystals showing both p and n regions.
The electrical resistivities were related to crystal compositions permitting the construction of the Pb‐Se phase diagram in a narrow region about the compound PbSe. The invariant melting point for the system falls in the Se‐rich region. This precludes the possibility of growing a crystal from a melt which is of stoichiometric composition throughout.
Theory of Linear Flame Propagation. Part I. Existence, Uniqueness, and Stability of the Steady State22(1954); http://dx.doi.org/10.1063/1.1740035View Description Hide Description
It is shown that the equations governing the steady, adiabatic, one‐dimensional propagation of single‐reaction flames admit an infinity of solutions, only one of which, however, can be realized physically. The steady state is shown to be stable against small perturbations, and the possibility of reconciling this result with apparently contradictory experimental data is discussed.
22(1954); http://dx.doi.org/10.1063/1.1740036View Description Hide Description
A quantitative approximate theory of flame structure in the steady state, including formulas for the determination of flame speeds, is set forth. The theory predicts that in a first approximation, the sensitivity of a steady deflagration wave to external perturbations depends upon the shape of the temperature profile, but not upon the speed or width of the wave, or the pressure. It is shown that the sensitivity increases with increasing dilution of the explosive mixture, in agreement with the explanation of inflammability limits suggested in Part I.
22(1954); http://dx.doi.org/10.1063/1.1740038View Description Hide Description
The Relation between Energy Levels of Substituent Groups and Electron Migration Effects in Some Monosubstituted Benzenes22(1954); http://dx.doi.org/10.1063/1.1740039View Description Hide Description
Determinations of the highest occupied (HB, HS ) and the lowest vacant levels (VB, VS ) were made with benzene and some substituent groups using experimental knowledge of their ionization potentials and their near ultraviolet absorption spectra. On the basis of the relative height of these levels, monosubstituted benzenes can be classified into following three groups: (1) | VS –HB | < | VB –HS | for meta‐directing molecules: (2) | VS –HB | > | VB –HS | for ortho‐, para‐directing molecules: (3) | VS –HB | ≈ | VB –HS | for styrene. By the aid of a simple quantum‐mechanical treatment, it becomes sure that in the case of (1) the interaction between levels VS and HB is predominant and the migrating electron flows out of benzene into the substituent: on the other hand in the case of (2) the interaction between levels VB and HS is the stronger and the migrating electron moves in the reverse direction: and finally, in the case of (3), both interactions referred to in the foregoing should be taken into account with almost equal importance.
Furthermore, it was shown that the difference in the ionization potential between the meta‐ and the ortho‐, para‐directing monosubstituted benzenes can be interpreted by taking into consideration the interaction of HB with HS or VS , and that the absorption bands in the wavelength region 2300∼2600A, observed with meta‐directing molecules, may be regarded as due to the transition between two levels which occur by the interaction between levels VS and HB .
22(1954); http://dx.doi.org/10.1063/1.1740040View Description Hide Description
The nature of an implicit assumption in a recent Fokker‐Planck treatment of the excluded volume problem is indicated. This assumption makes the results of the treatment conditional. It is shown that if one can verify the assumption, one can dispense with the use of a Fokker‐Planck equation.
22(1954); http://dx.doi.org/10.1063/1.1740041View Description Hide Description
Kinetic theory of phase transitions in which embryos of the new phase may grow or diminish by the acquisition or loss of monomer and dimer is presented. The error committed in neglecting the latter is shown to be negligible except in systems in which a large fraction of the old phase is present in the form of dimer.
22(1954); http://dx.doi.org/10.1063/1.1740042View Description Hide Description
The microwave spectrum of OH affords a new method of determining the abundance of OH in a low‐pressure gas mixture. This method applied to the products of a discharge in H2O shows that certain previous methods for detecting the presence of OH radicals in fact are not sensitive to OH, but to some other reactive components of a discharge in H2O. OH radicals are obtained from a discharge in concentrations near 10 percent and with a lifetime of approximately sec.