Journal of research of the National Bureau of Standards. Section A, Physics and chemistry最新文献

The spectrum of the neutral bromine atom, Br I, has been newly investigated by using electrodeless discharge tubes as light sources. The observations have led to a list of wavelengths and estimated intensities for 1253 spectral lines in the range 1067 to 24100 Å. The number of known energy levels has been increased to 123 even and 128 odd levels, as compared with the 27 even and 33 odd levels previously known. All predicted energy levels of the 4s ²4p ⁴ ns, up, nd, nf electron configurations from 0 to ~93250 K have been discovered. The observations in the vacuum ultraviolet establish that the positions of all the levels lying above those of the ground configuration as given in the compilation Atomic Energy Levels, Vol. II (1952) should be increased by 6.7 K. All but 26 faint lines of Br I have been classified. A total of 67 levels has been ascribed to the 4s ² 4p* nf configurations. It is demonstrated that the nf configurations exhibit almost pure pair coupling. The very regular (³P₂)nf[5]°_11/2 series yields for the principal ionization energy of Br I the value 95284.8 K.

The adsorption of poly(ethylene o-phthalate) from chloroform solution on glass powder and aluminum oxide was studied. The adsorption of a number of fractions, varying in number average molecular weight from 970 to 6250 showed a decrease in the moles of polymer adsorbed with increase in molecular weight. The results are interpreted to indicate that this polymer molecule lies in a relatively flattened conformation on the glass surface. More polymer was adsorbed on glass powder at 50 °C than at 0 °C. Adsorption on glass powder that had been outgassed to remove adsorbed water was less than on untreated glass. Initial adsorption at one temperature followed by exposure at the other temperature resulted in complete reversibility of sorption on the untreated glass. Decreasing the temperature from 50 to 0 °C resulted in desorption from the outgassed glass, but increasing the temperature did not result in additional adsorption. These differences are ascribed in part to adsorption across an adsorbed water layer on the untreated glass. An explanation for the "one-direction reversibility" observed for the outgassed glass is presented.

The three spectral types of muscovite sheet mica, i.e., very pink ruby, light green, and dark green, were subjected to heat treatments at temperatures up to 600 °C. The changes in the apparent optic axial angle and in the absorption spectra (0.3 to 15 μ) were studied along with color. The differentiation of muscovite sheet according to these spectral types extends to the behavior of apparent optic axial angle and to certain regions of the spectrum under heat treatment. The pink associated absorption region (0.47 to 0.6 μ) can be enhanced or bleached away by appropriate thermal treatment, although the associated infrared multiplet at 3 to 3.5 μ is little affected. The absorption band at 12 μ increases in intensity with temperature of treatment. It is suspected that the 0.47 to 0.6 μ absorption is the result of color centers.

A consideration of the deficiencies in standard methods used for the cryometric determination of purity has led to a new approach in which the measurement of an intensive rather than an extensive property is the controlling factor. This method, measurement of the dielectric constant as a function of the fraction melted and correlation with the accompanying change in temperature, allows calculation of purity with high precision. The apparatus used and experimental work performed to ascertain the scope of the method are described. Determination of purity for organic compounds with differing polarizabilities and dipole moments indicate a rather wide applicability of the method. The large change in the dielectric constant of a high purity compound as it passes from solid to liquid state, with an accompanying small change in temperature, may allow automatic control of temperature within extremely narrow limits.

A method has been developed for the precise assay of potassium dichromate by constant-current coulometric titration with ferrous ions generated at a platinum cathode. It, is shown that one-half gram samples of the dichromate can be titrated with a standard deviation of 0.003 percent.

Nucleophilic reactions of hexafluorobenzene and related polyfluorobenzenes were studied in detail. Reaction of hexafluorobenzene with hydroxides, alcoholates, aqueous amines, and organolithium compounds led to the substitution of one or more fluorine atoms. The structures of the products were determined, using near infrared and nuclear magnetic resonance spectra. Fluorine is replaced more readily than chlorine, bromine, iodine, or other groups. In the majority of the products in which two of the fluorines in hexafluorobenzene were replaced, the substituting groups were para to each other. However, depending on the reagents other orientation effects were noted. The reaction mechanisms were a function of reagents and conditions. The most prevalent mechanism is presumably the displacement of a fluoride anion by another anion, probably via the formation of transition complexes of different lifetimes. However, simple ionization or attack by neutral species may occur under some conditions. The diazotization and oxidation of pentafluoroaniline were also investigated.

The heat of oxidation of aqueous sulfur dioxide with gaseous chlorine has been determined by calorimetric methods. The results correspond to the reaction: $\begin{array}{c}{\text{Cl}}_2\left(g\right)+{\text{SO}}_2\cdot 2500H_{2}O+2502H_{2}O=H_2{\text{SO}}_4\cdot 2500H_{2}O+2\left(\text{HCl}\cdot 1250H_{2}O\right),\\ \Delta H\left(25°C\right)=-77.28\pm 0.14\text{kcal}/\text{mole}.\end{array}$ The heat of formation of aqueous sulfuric acid (in 2500 moles of water) has been calculated to be -213.92 kcal/mole.

The adsorption of polystyrene from cyclohexane below the theta temperature onto chrome ferrotype plate was studied by means of ellipsometry (polarization spectrometry). In this technique changes in the state of polarization of polarized light are measured upon reflection from a film-covered surface. The measurements were carried out in situ and permitted determination of the thickness and refractive index of the swollen polymer film at the solidsolution interface. A concentration range of 0.18 to 9.7 mg/ml was studied for polymer with a molecular weight of 76,000. The thickness of the adsorbed film increased with increasing solution concentration, reaching a plateau for most of the concentration range studied. The average thickness at this plateau was approximately 210 Å. The adsorbed film was highly swollen, consisting of about 12 g/100 ml of polymer for most of the concentration range. The amount adsorbed was determined to be approximately 2.25×10^-4 mg/cm² at the plateau. Comparison of the radius of gyration of polystyrene in solvent is made to the results obtained.