Index of content:
Volume 21, Issue 4, 01 April 1953
21(1953); http://dx.doi.org/10.1063/1.1698972View Description Hide Description
Diffusion coefficients are presented as a function of pressure to 10 000 atmospheres for the following systems:using S35 tagged CS2.
The results are interpreted in terms of the activation volume, enthalpy, and entropy, and conclusions are drawn concerning the effect of pressure on the structure of the liquids.
21(1953); http://dx.doi.org/10.1063/1.1698973View Description Hide Description
Diffusion coefficients are presented as a function of pressure to 10 000 atmospheres for the following systems:The results are interpreted in terms of the activation volume and the tetrahedrally coordinated structure of water. It is found that pressure tends to break down the structure, and in certain regions an increase in diffusion coefficient with pressure is noted.
In the salt solutions the water structure is controlling with some added effects due to solvation and ionic interaction.
21(1953); http://dx.doi.org/10.1063/1.1698974View Description Hide Description
Diffusion coefficients have been measured as a function of pressure to 10 000 atmos for the following aqueous solutions:and for 0.01 M HgCl2 in n‐butanol at 25° and 50°C. The results are interpreted in terms of the activation volume, and compared with previous data on water and sulfate solutions.
21(1953); http://dx.doi.org/10.1063/1.1698975View Description Hide Description
A technique has been developed for handling the extremely reactive interhalogen compounds which makes it possible to investigate their structures by x‐ray diffraction at low temperatures. As the first step in a program of study of the interhalogen group the crystal structure of chlorine trifluoride has been determined at −120°C. The chlorine trifluoride molecule is planar with the point group symmetry mm. The Cl atom is bonded to one F atom at 1.621A and to two F atoms at 1.716A. The F–Cl–F bond angle is 86°59′. In the succeeding pages of this journal, a parallel investigation of the vapor phase by microwave spectroscopy is presented by Dr. D. F. Smith. The molecular configuration is identical in the two cases.
21(1953); http://dx.doi.org/10.1063/1.1698976View Description Hide Description
A microwave spectrometer designed for the study of the microwave spectra of corrosive fluorine compounds has been used to observe and measure a portion of the microwave spectrum of chlorine trifluoride. A number of transitions have been identified, and from these the moments of inertia and quadrupole coupling coefficients of both Cl35F3 and Cl37F3 obtained. An intensity alternation was observed showing that the ClF3 molecule has a C2v axis and is planar. The moments of inertia confirm this and further show that ClF3 has a distorted ``T'' structure with one short (1.598A) and two long (1.698A) ClF bonds. The angle between the two different kinds of ClF bonds is 87°29′. The quadrupole coupling coefficients χ aa (Cl35F3)=−81·2 mc, χ bb (Cl35F3)=−64·7 mc, χ cc (Cl35F3)=146 mc agree with the observed frequency, f(Cl35F3)=75.1295 mc, of the pure quadrupole spectrum of ClF3, which corresponds to an eqQ of 150 mc.
21(1953); http://dx.doi.org/10.1063/1.1698977View Description Hide Description
The process of chemical stress relaxation in elastomers is examined in some detail. It is predicted that in some cases it will be possible to determine the location of the chemical bond broken. The special cases of relaxation due to scission of cross links and random scission of the polymer are calculated. The shapes of the stress vs time curves are widely different.
21(1953); http://dx.doi.org/10.1063/1.1698978View Description Hide Description
Measurements of shock front thicknesses in argon by the reflectivity method have been extended to Mach 2.09, and the shape of the front has been investigated by comparing the experimental results with the reflectivity expected on the basis of five simple models for the density change through the front. The thicknesses agree with Zoller's calculations but for the strongest shocks are considerably greater than those of other theoretical estimates. The magnitude and form of the reflectivity (as a function of λ/L cosθ) of shock fronts in three diatomic gases have been used to study the rate of equilibration of rotational with translational energy. Hydrogen requires more than one hundred and fifty collisions for this equilibration, while nitrogen and oxygen equilibrate much more rapidly. For the latter two gases there is evidence that at least two relaxation times are involved in the equilibration.
Adiabatic Correlation Rules for Reactions Involving Polyatomic Intermediate Complexes and their Application to the Formation of OH(2Σ+) in the H2–O2 Flame21(1953); http://dx.doi.org/10.1063/1.1698979View Description Hide Description
Adiabatic orbital and spin correlation rules applicable to a detailed study of elementary chemical reactions involving nonlinear polyatomic intermediate complexes have been formulated and are presented together with some pertinent correlation tables. These correlation rules and tables permit the determination of the adiabatically allowed term manifold of reaction products from the states of the separated reactants without reference to their detailed electronic configurations. The formulation presented here utilizes group theoretical arguments relating to the symmetry properties of the reactants, the intermediate reaction complex, and the products and is based principally upon the results obtained previously by Mulliken for the resolution of species into those of point groups of lower symmetry. The effects of the change of the (geometrical) configuration of the intermediate reaction complex during reaction and of the electronic‐vibrational coupling on these correlations have been considered in detail. It is concluded that strict orbital electroniccorrelation rules are operative only for reactions where neither the reactants nor the products are polyatomic. For reactions involving polyatomic reactants and/or products, the vibrational‐electronic coupling weakens the simple orbital electronic correlations so that detailed vibroniccorrelations will be necessary. The spin correlation rules, however, are not affected by these interactions and are identical with those given by Wigner and Witmer for atomic and diatomic systems.
These correlation rules are then applied to a study of the reactions which may be of importance in the production of electronically excited OH[OH(2Σ+)] in the hydrogen‐oxygen flame. The mechanism of these reactions is investigated with special reference to the predissociating OH(2Σ−) state discussed recently by Gaydon and Wolfhard. It is suggested that the interaction of and the consequent radiationless transition between HO2 intermediate reaction complexes is primarily responsible for the formation of OH(2Σ+) in its observed vibrational nonequilibrium distribution with the specific enhancement of the levels v′=2 and 3.
The adiabatic correlations for the special case of association (and dissociation) reactions involving linear polyatomic intermediate complexes and products are considered briefly in the Appendix. It is concluded that vibronic correlations are required for the determination of the product term manifold for these reactions.
21(1953); http://dx.doi.org/10.1063/1.1698980View Description Hide Description
The paper discusses the relation of the relaxation time τ of a dielectric to the measured decay time of polarization T and proposes a new expression for the internal field in a dielectric subjected to an alternating field. It is found for this expression that and that in most instances no serious error is incurred in using T instead of τ. Application to the case of several distinct relaxation times shows that the new expression gives relations between the complex dielectric constant and frequency which are observed experimentally.
21(1953); http://dx.doi.org/10.1063/1.1698982View Description Hide Description
The absorptionspectrum of single crystals of Nd(BrO3)3·9H2O was photographed in the visible and near infrared and ultraviolet in σ and π polarizations. Empirical energy level diagrams are presented for some of the groups of lines, and in this way it is found that the 4 I 9/2ground state is split in the electric field into five levels at 0, 115, 184, 363, and 382 cm−1. An analysis is made of the spectrum based on a Russell‐Saunders coupling model and a knowledge of the expected splitting of the levels of the free Nd+++ ion in the electric field of the crystal. The electrostatic interaction energies of terms arising from f 3 electrons were computed by the Slater method and the results agree with those previously given by Racah. The Landé interval factors were also computed in order to predict the multiplet splitting. Trial values of the parameters were first found by extrapolation mainly from Pr+++. Selection rules for transitions in an electric field of C3v symmetry are presented, and the results applied to the neodymium bromate spectrum indicate that the transitions are not purely electric dipole, quadrupole, or magnetic dipole alone.
21(1953); http://dx.doi.org/10.1063/1.1698983View Description Hide Description
21(1953); http://dx.doi.org/10.1063/1.1698984View Description Hide Description
The accommodation coefficient method of Roberts was used to measure the adsorption isotherms of the upper molecular oxygen film on tungsten at 25 and 100°C and at pressures from 9×10−9 to 1×10−4 mm Hg. The isotherms were found to fit Wang's theoretical isotherm for a mobile film with repulsive interaction. An entropy of adsorption was calculated from the surface pressure by Hill's method and found to be about four entropy units at low film concentrations. The large discrepancy between calculated and theoretical entropies suggests either or both irreversible effects and nonlinearity of the relation between accommodation coefficients and surface coverage. The minima which are exhibited during the growth with time of the adsorbed film at 100°C may be direct evidence for the presence of holes in the immobile first layer which are filled by activated diffusion from the upper layer.
21(1953); http://dx.doi.org/10.1063/1.1698985View Description Hide Description
The rate of the homogeneous three‐body recombination of iodine atoms, , is measured. A short intense pulse of light from a flash lamp dissociates 1–9 percent of the ca 1018 iodine molecules in a 200‐cc cell, and the subsequent recombination of iodine atoms is followed by fast photoelectric techniques.
The measured values of k at room temperature are 4.2(±0.4)×109 liter2 moles−2 sec−1 (argon), 58(±4)×109 (neopentane), 65(±6)×109 (pentane). The value for neopentane is the same at 200°C.
The large values of the recombination rate constants indicate that an important recombining process consists of a ``sticky'' collision between an I atom and an M molecule or atom, leading to the formation of a complex IM, which reacts with a second I atom. The lifetimes of the collision complexes are estimated.
The rates of the reverse process, the dissociation of I2 by collision with M, are calculated; the pre‐exponential factors are extraordinarily large.
The extinction coefficients of gaseous iodine have been remeasured.
21(1953); http://dx.doi.org/10.1063/1.1698986View Description Hide Description
Sodium nitrate, potassium nitrate, and potassium chlorate have been exposed two to four weeks in the experimental thimble of the Argonne Heavy Water Pile. After exposure these salts evolve a gas when dissolved in water or when melted or heated to a crystal transition point. The gas yields are in sodium nitrate ca 0.3, in potassium nitrate ca 0.8, and in potassium chlorate 2.0–3.0 molecules gas/100 ev. For the nitrates this gas has been shown to be largely oxygen which is trapped during irradiation in the gaseous form in small pockets in the crystal. This conclusion is based on the paramagnetism of the irradiated crystals, on chemical analysis of the evolved gases, and on measurements of the amounts of gas liberated in crushing experiments. When irradiated crystals are heated below the melting point, the gas pockets grow and coalesce, this being accompanied by a decrease in crystal density. In irradiated nitrates, oxygen and nitrite ion are formed in equivalent amounts. Experiments with low energy x‐rays indicate that most of the decomposition results from electronic ionization and excitation and not from elastic collision of the bombarding particles.
21(1953); http://dx.doi.org/10.1063/1.1698987View Description Hide Description
The following bands have been located in the far infrared spectra by the method of residual rays: cis‐dichloroethylene at 170 cm−1; trans‐dichloroethylene at 265 cm−1 and 192 cm−1; phosphorus trichloride at 190 cm−1; trans and ``gauche'' 1,2 dichloroethane at 223 cm−1 and 125 cm−1; propylene at 177 cm−1; acetaldehyde at 245 cm−1 and 120 cm−1; methyl alcohol at 190 cm−1, 161 cm−1, and 120 cm−1; carbon suboxide at 192 cm−1.
21(1953); http://dx.doi.org/10.1063/1.1698988View Description Hide Description
It has been shown that the fluorescence of biacetyl vapor at 25°C excited with 3650A radiation does not decay as a simple exponential function of time. After flash excitation, there is a ``fast'' fluorescence followed by a slow exponential decay. The quenching of the fluorescence has also been studied at several temperatures, pressures, and in the presence and absence of oxygen gas. A consideration of this and previous work permits a further elucidation of the fluorescence phenomena in terms of two upper emitting states. Fluorescence from the state responsible for most of the fluorescence at room temperature is quenched strongly by oxygen and is apparently completely removed at 200°. Fluorescence from the other state is unaffected by oxygen and is still measurable at 200°.
21(1953); http://dx.doi.org/10.1063/1.1698989View Description Hide Description
The infrared spectrum of a‐C2H2D2 has been obtained, and the vibrational frequencies used to complete the calculation of the force constants of C2H4. The spectra of C2H3D, trans‐C2H2D2, and a mixture of cis‐ and trans‐C2H2D2 were also observed and used to check the force‐constant calculations.
21(1953); http://dx.doi.org/10.1063/1.1698990View Description Hide Description
The effect of spectral line shape on apparent rotational temperatures of OH has been investigated for the P 1 branch, 2Σ→2Π transitions, (0, 0) band, by treating the ratio of collision half‐width to Doppler half‐width as a variable parameter. The results of calculations for emission experiments, using conventional plots, show a large effect of line shape on apparent temperature. In general, the greater the ratio of collision half‐width to Doppler half‐width, the smaller the distortion of experimental data. The analysis predicts higher apparent rotational temperatures for isothermal systems at reduced pressures than at atmospheric pressures. Although this result is in agreement with experimental observations on flames, it cannot be used as an explanation for the observed data without auxiliary studies proving that distortion of data is of importance in any given case. The two‐path method for determining temperatures and emissivities (concentrations) in flames has been extended to spectral lines with combined Doppler‐ and collision‐broadening.
21(1953); http://dx.doi.org/10.1063/1.1698991View Description Hide Description
The low velocityscattering of H+, H2 +, and H3 + in both methforane and ethforane has been measured at ion velocities of less than 150 volts. Ion neutralization was detected and measured for all three ions in both fluorocarbons and elasticscattering potential functions evaluated for all six interactions. These measurements are compared with similar ones made on the hydrocarbons methane and ethane.
21(1953); http://dx.doi.org/10.1063/1.1698992View Description Hide Description
The isothermal order‐dependent change in the Young's modulus of a single crystal of Cu3Au is measured as a function of time at various temperatures in the range 279.3°C to 384.3°C. These temperatures were reached by quenching rapidly from an equilibrium state 28.2°C above the critical temperature (386.0°C).
The time variations of Young's modulus indicate two distinct stages of the disorder‐order transformation. The initial stage starts immediately and is completed a few minutes after quenching, while the later stage requires a few minutes before starting and then proceeds very slowly toward an equilibrium state. ``Relative relaxation times'' are associated with each of them.
In conformance with the work of Sykes and Evans and others, the initial stage is described as the formation of contiguous, antiphase, ordered domains by means of normal atomic interdiffusion. The later stage consists of the coalescence of these domains and requires at least two different geometrically constrained diffusion processes.