Index of content:
Volume 23, Issue 9, 01 September 1955
23(1955); http://dx.doi.org/10.1063/1.1742386View Description Hide Description
In pure silicagel,irradiation with 2 to 8×1018 fast neutrons/cm2 produced a significant increase in catalytic activity for the double‐bond isomerization in hexene. The effect is believed to be due to lattice dislocations.
23(1955); http://dx.doi.org/10.1063/1.1742388View Description Hide Description
Several collision integrals useful for the calculation of the second approximation to the thermal diffusion factor have been evaluated for the Lennard‐Jones 12:6 model and utilized to calculate [RT ]2, the second approximation to the thermal separation ratio from the expressions developed by Mason for the exp‐six model. It has been shown that the difference between [RT ]1 and [RT ]2 for the 12:6 model is very small and does not vitiate the method developed by us elsewhere for calculating the force constants from the thermal diffusion data. These considerations have been applied to argon and the results compared with the experimental data. A simple empirical relation connecting [RT ]1 and [RT ]2 has been derived for the Lennard‐Jones 12:6 model.
23(1955); http://dx.doi.org/10.1063/1.1742389View Description Hide Description
The existing experimental data on the low‐temperature fluorescence and absorption of naphthalene crystal is reviewed and correlated with our own data. Some preliminary work on crystals of C10D8 is included. A vibrational analysis of the first moderately strong absorption region, 31 476—33 700 cm—1 is made on the basis of the corresponding absorption of naphthalene in solid solution with durene. Some constants of the exciton theory of molecular crystals are obtained for the first and second excited singlet molecular states. Some discrepancies with the theory are pointed out; one of these is removed by calculating the crystal induced mixing of the two excited molecular states. Factor group splitting is found for certain vibronic levels of the ground and first excited state, but most vibronic levels of these states do not split appreciably.
23(1955); http://dx.doi.org/10.1063/1.1742390View Description Hide Description
The thermal conductivities of binary mixtures of organic vapors have been investigated in the temperature range 60—125°C. When nonpolar vapors of similar viscosity and molecular weight are used, the variation of conductivity with composition of the mixture is roughly linear. Mixtures of nonpolar and strongly polar vapors, on the other hand, exhibit pronounced maxima in the conductivity vs composition curves. The difference in behavior is due to the strong interaction between polar molecules on collision.
23(1955); http://dx.doi.org/10.1063/1.1742391View Description Hide Description
An optical system has been made so that absorption and emission spectra from stages of a combustion process can be observed. Spectra from the two‐stage cool flame of diethyl ether indicate that carbonyl compounds are formed as intermediates and final products are HCHO, CO2, H2O, CO, and C2H4. Also identified are CH3OH and CH4. Temperature calculations indicate that the infrared emission from this reaction is of thermal origin in contrast to the visible emission which is undoubtedly chemiluminescence. Calculated temperatures range from 700°K in the first cool flame to ∼1000° in the second‐stage flame.
23(1955); http://dx.doi.org/10.1063/1.1742392View Description Hide Description
An investigation of the oxidation states of P32 formed by neutron irradiation of KCl shows that like the simultaneously formed S35 the ratio of the different oxidation states depends on the preirradiation treatment. Through outgassing of the crystals results in the production of lower oxidation states. On the other hand, the oxidation states of P32, unlike S35, are strongly affected by the presence of x‐ or γ radiation. The recoil energy of the newly formed P32 fragment seems to have little effect on its final oxidation state.
23(1955); http://dx.doi.org/10.1063/1.1742393View Description Hide Description
A calculation is made of the correction for the volatility of mercury which should be applied to observed pressures of compressed gases, when mercury is used as the confining fluid. The usual correction is simply the subtraction of the normal vapor pressure of mercury corrected for the effect of hydrostaticpressure (the Poynting effect). Here we show that this is an inadequate treatment of the problem, as the mixture of mercury atoms and compressed gas cannot behave as an ideal mixture. An estimation of the intermolecular forces between mercury atoms and the added gas leads to values of the virial coefficients from which a revised correction can be computed, assuming that the system is at equilibrium. This revised correction can be considerably larger than the usual correction and is often of opposite sign.
23(1955); http://dx.doi.org/10.1063/1.1742394View Description Hide Description
In the region between 475 and 3500 Mc/sec one P‐branch and five Q‐branch lines in the spectrum of HDO have been completely measured and identified. These data have contributed materially to an evaluation of the structural constants of the molecule. From the data obtained by this and other microwave spectroscopy projects we have computed the principal moments of inertia, respectively, as having the values of 1.1982, 3.0862, and 4.3887 in units of gm cm2×10—40. In addition, the shape of the 32 → 33 line at 824.64 Mc/sec has been extensively studied. At low pressure the wings of the line have been shown to be wider than is consistent with the Lorentz line shape probably due to the presence of sattelite lines arising from the hyper‐fine splitting of the energy levels by the quadrupole moment of the deuteron. The observed effects are consistent with a quadrupole coupling constant of 272±90 kc/sec with respect to an axis along the O–D bond.
23(1955); http://dx.doi.org/10.1063/1.1742395View Description Hide Description
Infrared spectroscopic studies have been made of the solid formed when the products of the glow‐discharge decomposition of hydrazoic acid are condensed on a surface cooled to 90°K. Spectra were obtained at several temperatures as the solid was allowed to warm to 230°K. The solid shows absorptions attributed to HN3, NH4N3, and NH3, and to two intermediate species in the reaction. These intermediates are interpreted to be N2H2 and (NH) x , where x may be equal to 4. The presence of the imine radical, NH, in the solid at 90°K is inferred.
23(1955); http://dx.doi.org/10.1063/1.1742396View Description Hide Description
Sr or Ba was deposited on W ribbon receivers by evaporation from source filaments in which a chemical reaction produced the metal at least 99.7% pure. The receiving surfaces could be cleaned at will by heating to high temperatures; repeated tests were thus possible. By thermionic measurements, adsorption and desorption were observed independently under nonequilibrium conditions. By using radioactive Sr isotopes, the deposit corresponding to any thermionic activation was measured. For each ribbon, thermionic activation was apparently a reversible function of the amount adsorbed.
Our experimental methods give information on kinetics, rather than equilibria. The adsorption mechanism more nearly resembles that proposed in Langmuir's later papers rather than that of his earlier theories but treatment of desorption by the theory of absolute reaction rates is considerably more satisfactory. This accounts for desorption kinetics over the experimental temperature range by only two disposable constants, the activation energy for desorption, (a.e.d.), and a repulsive energy of interaction between adatoms.
The work function [open phi] for a monolayer of Sr is ∼2.2 v and for Ba is ∼1.9 v. The thermionic activation is explained in terms of polarized adatoms, rather than by the usual assumption of partial ionization, which has no experimental justification for Ba or Sr films. The theory proposed gives a reasonable value for the polarizability of Sr and of Ba, which when substituted into the theory of Prosen, Sachs, and Teller predicts a heat of physical desorption agreeing well with the observed a.e.d. This also agrees with the heat of desorption (h.d.) determined by the usual method of applying the Clapeyron equation to kinetics of this kind. We therefore believe that this adsorption should be called ``physical,'' rather than ``chemical,'' although the mean a.e.d.'s are, for Sr 77.4, and for Ba 80.7 kcal/mole, considerably larger than for most examples of chemisorption.
23(1955); http://dx.doi.org/10.1063/1.1742397View Description Hide Description
The exchange of radioactive F18 between hydrogen fluoride and fluorine has been studied over a wide range of concentrations at three temperatures in the range 194° to 257°C. The exchange may be accounted for entirely by a heterogeneous catalysis mechanism involving competitive adsorption of the Langmuir‐Hinshelwood type. Experiments have been performed indicating the important role of surface treatment on the kinetics of the exchange.
23(1955); http://dx.doi.org/10.1063/1.1742398View Description Hide Description
Absorption cross sections of CO2 and CO in the region from 1306 A to 374 A have been measured. The absorptionspectrum of CO2 consists of strong resonance bands between 1306 A and 700 A, with one of them at 923 A showing an unusually large cross section of 117×10—18 cm2. A continuum with bands superimposed on it was observed to start at about 860 A or 14.4 ev which corresponded to the first ionization potential of CO2. From 700 A toward shorter wavelengths, the contour of the continuum was better defined and smooth with a broad maximum of 36×10—18 cm2 at 550 A and a total f‐value of 4.4. The CO absorption between 1306 A and 955 A was less than 10—18 cm2. Prominent resonance bands appeared at 924 A and extended to 600 A. An absorption continuum could be identified between 876 A and 374 A showing maximum values of σ≃19×10—18 cm2 between 750 A and 550 A with perhaps a small dip of 15×10—18 cm2 at 644 A. The f‐value of this continuum was 2.8.
23(1955); http://dx.doi.org/10.1063/1.1742399View Description Hide Description
23(1955); http://dx.doi.org/10.1063/1.1742401View Description Hide Description
The absorption characteristics of helium adsorbed on TiO2 (anatase) have been studied in the temperature range 2°—20°K. Isotherms are reported at 2.60°, 4.17°, 13.96°, and 20.28°K. Isosteric heats of adsorption at low coverage have been measured at 17.1°K. The data are interpreted in terms of a previously discussed model.
23(1955); http://dx.doi.org/10.1063/1.1742402View Description Hide Description
Cyclopropane‐d 6 has been synthesized from deuterium oxide and magnesium tricarbide in steps giving successively methyl acetylene‐d 4, propylene‐d 6, allyl chloride‐d 5, 3‐bromo‐1‐chloropropane‐d 6, and cyclopropane‐d 6. Infrared spectra of cyclopropane and cyclopropane‐d 6 have been obtained in the spectral region 350 to 3700 cm—1 for the vapor and 650 to 3700 cm—1 for the liquid. Raman spectra, including semi‐quantitative depolarization factors, have been determined for the liquid state. The spectroscopic results satisfy the Teller‐Redlich product rule for a molecule of D 3h symmetry. All active fundamentals in cyclopropane‐d 6 but one have been directly observed. The inactive fundamentals in both molecules have been located provisionally from overtone assignments. An attempt to determine the molecular geometry from rotational contours of the infrared bands was not successful, but high‐resolution work on cyclopropane‐d 6 shows that the C–C distance is 1.524±0.014 A.
23(1955); http://dx.doi.org/10.1063/1.1742403View Description Hide Description
The intermolecular potentials of argon, krypton, and xenon are investigated using the recently measured second virial coefficients and the crystal properties at 0°K. The potential functions considered are the 9:6, 12:6, and exp:6. The methods of determination of parameters are reviewed and the method of least squares used in this paper described. All the potentials fitted the second virial coefficient very well, but with the same parameters fitted the crystal properties only moderately well.
23(1955); http://dx.doi.org/10.1063/1.1742404View Description Hide Description
The magnetic susceptibilities of U(SO4)2·4.22H2O, U(C2O4)2·6H2O, UF4·NaF, (γ)UF4·2NaF, and UF4·3NaF have been measured in the temperature range from 14°K to 300°K. The results are presented in graphical form and their general form is discussed. The susceptibilities of all five compounds appear to approachfinite values at 0°K.
23(1955); http://dx.doi.org/10.1063/1.1742405View Description Hide Description
A perturbation theory of the excluded volume effect in chain polymers is developed. The theory is applied to the mean square end‐to‐end distance, 〈L 2〉, of a linear chain (second‐order perturbation), and to the mean square radius of a linear and a branched chain (first‐order perturbation). Flory's approximate theory is found to be in fair agreement with the second‐order perturbation theory. Integro‐differential equations are developed to discuss the behavior of 〈L 2〉/nb 2 as n→ ∞, for a chain composed of n segments of length b.