Index of content:
Volume 22, Issue 1, 01 January 1954
22(1954); http://dx.doi.org/10.1063/1.1739812View Description Hide Description
Raman and infrared spectra have been obtained for trimethylphenylsilane, hexamethyldisilylmethylene, hexamethyldisiloxane, hexamethyldisilazine, and hexamethyldisilane. For the last compound the infrared spectral region covered extended from 1—50 microns; for the other compounds the region extended only from 1—15 microns. The intensities and depolarization factors of the Raman bands have been determined photoelectrically. A few tentative frequency assignments have been given.
Irradiation of Ferrous Ammonium Sulfate Solutions: Energy Absorption and Ionization Calculations for Cobalt 60 and Betatron Radiation22(1954); http://dx.doi.org/10.1063/1.1739858View Description Hide Description
Solutions of ferrous ammonium sulfate in 0.8N H2SO4 have been irradiated with Co60gamma rays and with x‐rays from a 25‐Mev betatron. The energy absorbed per unit volume of solution has been calculated from a modification of the Bragg‐Gray formula, Ev =JvW ρ in which the factor ρ was determined according to a calculated distribution of primary electron energies. The chemical yield was then calculated in terms of G, the number of ferrous ions oxidized per 100 ev absorbed.
22(1954); http://dx.doi.org/10.1063/1.1739820View Description Hide Description
Quantitative kinetic data on the isotope‐exchange reaction of fluorine with chlorine trifluoride, bromine pentafluoride, and iodine heptafluoride have been obtained using F18 (t ½=112 min) tracer. The materials were handled in a metal vacuum line, and the exchanges were carried out in a 2‐liter nickelreaction vessel at three temperatures in the range 181—257°C. While the experimental data do not uniquely determine the mechanism, they strongly suggest that exchange takes place either through a heterogeneous catalysis by the metal fluoride coating on the walls of the reaction vessel, or by a combination of the heterogeneous mechanism plus a homogeneous gas‐phase exchange in those cases where a measurable amount of dissociation of the halogen fluoride occurs at the temperature of exchange. It has been shown to be unlikely that the observed exchanges take place through either an atomic mechanism or a purely homogeneous mechanism. It has also been shown that all fluorine atoms in the halogen fluoride molecules are exchangeable.
22(1954); http://dx.doi.org/10.1063/1.1739848View Description Hide Description
The absorption and luminescencespectra of triphenylmethyl, tri‐p‐xenylmethyl, phenyl‐di‐p‐xenylmethyl, diphenyl‐p‐xenylmethyl, and their cations have been determined. Polarization of the luminescence of each substance under excitation by plane polarized light has been examined. Assignment of symmetry classifications to the energy levels of these substances has been attempted.
22(1954); http://dx.doi.org/10.1063/1.1739849View Description Hide Description
A theoretical analysis is given of the fluorine magnetic resonance shifts in molecules. It is shown that the large range of shifts among different fluorine compounds arises from the effects of binding on the magnetic fields at the nucleus produced by the orbital motion of the electrons in the unfilled valence shell. The simple dependence on ionic character of the bond is also explained. The chemical shift between F2 and HF is calculated to be 14×10—4 compared to the experimentally observed value 6.3×10—4.
Bromination of Hydrocarbons. VII. Bromination of Isobutane. Bond Dissociation Energies from Bromination Kinetics22(1954); http://dx.doi.org/10.1063/1.1739850View Description Hide Description
The kinetics of the gas phase photochemical bromination of isobutane to yield 2‐bromo 2‐methylpropane was investigated in the temperature range 40—95°C and the reaction found to proceed through an atom and radical chain mechanism analogous to that observed with a number of other hydrocarbons. The thermal reaction was studied at 112 and 130°C and shown to have the same mechanism except for the mode of production of bromine atoms. Bromination was inhibited by hydrogen bromide, a product of the reaction, and also by oxygen. The dissociation energy of the tertiary C–H bond in isobutane was found to be 89.6 kcal/mole at 0°K, in agreement with the idea that tertiary bonds are considerably weaker than primary bonds. A general review of activation energies of bimolecular reactions involved in bromination is given as well as a recapitulation of values of C–H and C–C bonddissociation energies derived from bromination studies.
22(1954); http://dx.doi.org/10.1063/1.1739851View Description Hide Description
A detailed account of the appearance of and the constants derivable from the infrared absorption spectra of the active fundamentals v 2 and v 3 of C14O2 is given. The following constants have been determined: v 2 = 632.20 cm—1, v 3 = 2225.85 cm—1, B 000 = 0.39078 cm—1, α3 = 0.00293 cm—1. The harmonic frequencies ω i and the anharmonic constants x ij for the three isotopic species have been determined. Excellent agreement is obtained between observed and calculated band centers.
22(1954); http://dx.doi.org/10.1063/1.1739852View Description Hide Description
The effect of changing the dielectric constant and the effect of changing the ionic strength on the reaction between thiosulfate ion and ethyl bromomalonate have been studied. The rates of the ion‐molecule reaction could be accounted for on the basis of the simple second‐order mechanism between the dipolar ester molecule and the thiosulfate ion represented by the equationand considering the change of ionic strength with extent of reaction to be secondary in importance.
The reactions of thiosulfate ion and ethyl bromomalonate was studied at 0.1°C and at 25°C. The specific reaction rates for this reaction conformed to the prediction of the Amis‐Jaffe equations with respect to changing ionic strength and conformed to the Amis equation with respect to changing dielectric constant.
22(1954); http://dx.doi.org/10.1063/1.1739853View Description Hide Description
The structure of the monomer of formic acid was determined by the sector‐microphotometer method in electron diffraction. The equilibrium distances are C=O = 1.23±0.01A, C–O = 1.36±0.01A, O–O = 2.27 ±0.005A, and angle OCO = 122.4°±1°. The average displacements from equilibrium due to the molecular vibrations are listed in Table I.
22(1954); http://dx.doi.org/10.1063/1.1739854View Description Hide Description
A study of the heat conductionequation for reactions going on in a spherical flask leads to a calculation of three parameters, τ the mean lifetime for the establishment of stationary states, ΔT m the maximum temperature difference between the walls of the vessel and the reacting gas, and the average temperature difference 〈ΔT m 〉Av. These are given by in which ρ is the density, c v the specific heat at constant volume, r 0 the radius of the vessel, K the coefficient of thermal conductivity,R the specific rate of reaction, and H the heat of reaction.
In liquid systems under usual conditions τ is of the order of r 0 2 minutes (r 0 in cm) while 〈ΔT m 〉Av is about ±0.2°C (for H = ±10 kcal, half‐life = 1 hour, r 0 = 5 cm) so that such effects are usually negligible. In gases on the other hand 〈ΔT m 〉Av can be of the order of magnitude of 2°C or higher depending on the various conditions, resulting in significant errors in observed rate constants and activation energies. The effects of added inert gases, pressure, vessel packing, and other parameters are discussed. A very crude treatment of convection shows that it is not expected to alter appreciably the magnitude of 〈ΔT m 〉Av.
22(1954); http://dx.doi.org/10.1063/1.1739855View Description Hide Description
22(1954); http://dx.doi.org/10.1063/1.1739856View Description Hide Description
Neutron bombardment of liquidcarbon tetrachloride yields 38.5 min Cl38, and approximately 40 percent of the induced activity is retained in organic form. Dissolved chlorine reduces this retention in a regular fashion to approximately 25 percent at a concentration of 6 mole percent. Allyl chloride increases retention to 53 percent in equivalent concentrations. Neither of these ``scavenger effects'' is significantly dependent on the intensity of total dose of concomitant nonactivating pile radiation. This rules out the radiation‐decomposition theory of scavenger action and supports an atom‐radical diffusion‐recombination mechanism.
22(1954); http://dx.doi.org/10.1063/1.1739857View Description Hide Description
Experiments reported by other workers have shown that when a precipitate of silver bromide is shaken with a solution containing either silver or bromide ions, some of which are radioactive, the radioactive strength of the solution decreases. The final value reached corresponds to a uniform distribution of the active material throughout both solid and solution. No agreement on the interpretation of these results has up until now been reached. Two possible mechanisms for this exchange are described, and their consequences are examined. A new theoretical treatment is given which includes a consideration of the effect of the spread in crystal sizes, which was neglected in previous discussions of the problem. From those results, a new method of comparison between theory and experiment is suggested. This shows unambiguously that the exchange of silver ions is in agreement with predictions based on the hypothesis that the ions diffuse through the solid. It is shown that the exchange of bromide ions cannot be explained in this way. Values obtained for the diffusion constant of silver are in fair agreement with those from other sources. The relation of these results to the various suggestions put forward by other workers is discussed.
22(1954); http://dx.doi.org/10.1063/1.1739859View Description Hide Description
The radiation‐induced reaction between iodine and n‐heptane has been studied with a view to its use in the quantitative determination of free radical production in the radiolysis of liquid hydrocarbons. The yield of this reaction has been found to be nearly independent of iodine concentration and of temperature of the sample. The reaction is inhibited by the presence of dissolved oxygen. For each mole of hydrogen produced, 0.6 mole of iodine is absorbed which indicates that free radical production is a major component of the over‐all process. The primary decomposition yield is of the order of 10 bonds broken per 100 ev of absorbed energy.
22(1954); http://dx.doi.org/10.1063/1.1739860View Description Hide Description
22(1954); http://dx.doi.org/10.1063/1.1739861View Description Hide Description
A microwave spectroscope, especially designed for studies of the temperature dependence of microwave line widths is described. With this spectroscope, the line width of the J=1—2 OCS line has been measured over a temperature range from 195°K to 476°K. Over this range, the line width varies as T ‐0.9. An interpretation in terms of intermolecular forces is deferred, pending work with other linear molecules and other transitions.
22(1954); http://dx.doi.org/10.1063/1.1739862View Description Hide Description
The effect of the difference in asymmetry of the ground and excited states of a vibrttional band on the line strengths of the vibrational‐rotational transitions has been investigated. It is found that for sufficiently large Δk (∼0.1—0.2) in A‐ and C‐type bands there is an enhancement of the line strengths of either the R or P branch, depending on whether or not k of the ground state is greater or less than k of the excited state. In B‐type bands certain sub‐bands are enhanced, but in general no branch of the band is enhanced as a whole.
22(1954); http://dx.doi.org/10.1063/1.1739863View Description Hide Description
By means of microwavespectralmeasurements the following molecular parameters have been determined: 1. The dipole moment of NF3 is 0.235±0.007 Debye. 2. The nuclear quadrupole coupling of arsenic in AsCl3 is —173±20 Mc. 3. The internuclear distance Sb–Cl and the bond angle Cl–Sb–Cl are 2.325±0.005A and 99.5±1.5°, respectively, in SbCl3.
The measured molecular parameters of the group V‐trihalides are assembled and interpreted in terms of s—p hybridization, partial ionic, and partial multiple bond character. In particular, certain regularities in the dipole moments are pointed out which indicate that apparent anomalies in the dipole moments of these molecules can be understood in terms of s—p hybridization.
From the evidence of nuclear hyperfine structure, it appears that NF3 and AsH3, as was previously suggested for NH3, have an s—p hybridization which is not simply related to the bond angles. The quadrupole coupling per p‐electron of N14, previously reported to have been established by the measurements on NF3, has been again thrown open to question.
22(1954); http://dx.doi.org/10.1063/1.1739864View Description Hide Description
From the pure rotational spectra of several different isotopic species of CH3HgCl it is shown that dCHg=2.061±0.02A, dHgCl=2.282±0.005A, and ∠CHgCl=180°. Similarly, for CH3HgBr it is shown that dCHg=2.074±0.015A, dHgBr=2.406±0.005A, and ∠CHgBr=180°. Nuclear quadrupole couplings evaluated are Cl35=—42 Mc, Cl37=—33 Mc in CH3HgCl, and Br79=350 Mc, Br81=290 Mc in CH3HgBr. These indicate ionic character of 62 percent for the HgCl and 55 percent for the HgBr bond in these molecules, and lead to a value of 1.7 to 1.8 for the electronegativity of divalent mercury.
22(1954); http://dx.doi.org/10.1063/1.1739865View Description Hide Description
The available mathematical solutions for fixed‐bed concentration histories apply primarily to one‐component systems in adsorption and to two‐component systems in ion exchange. Thomas has developed explicit general relations for the saturation of an adsorbent bed initially free of saturating component by a fluid phase containing only this component; as well as for the converse elution situation.
These results are extended here to cases of mixed binary feeds (in ion exchange), and cases of columns that are uniformly partially saturated prior to the run under study. New definitions of the dimensionless parameters that characterize the sorption processes render the existing numerical framework applicable for evaluating this broadened range of operating conditions. From the theoretical standpoint, these new parameters clarify the mathematical interrelationships between adsorption and ion exchange, between saturation and elution, and between sorption of trace components and sorption of gross or bulk components. A method is suggested for calculating physical‐adsorption operations which do not conform to Langmuir isotherms.
Calculation procedures based upon this approach are illustrated by an idealized but representative example.