Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry最新文献

The chemiluminescent reaction of Pb + O₃ has been studied using both "cold" and vibrationally excited O₃. Emission from new states a and b has been observed in addition to the A and B states. The reaction of vibrationally excited O₃ with Pb to yield PbO(A) appears to be faster than that using "cold" O₃.

A list of about 9500 classified lines of Th I in the range 2345-29 662 Å is given. Lines in the range 2345-9239 A were observed and measured at NBS. Zeeman effect data for 2281 lines are listed. Lists of 254 even and 322 odd levels including their g values are presented. Among them there are 72 new levels, which were not contained in earlier publications.

The extinction coefficient of NO₂ has been measured in the spectral range 185 to 410 nm as a function of temperature between 235 and 298 K. In order to correct for the effect of the dimer absorption, the extinction coefficient of N₂O₄ has also been measured. The effect of a decrease in temperature upon the NO₂ absorption is a reduction in the extinction coefficient of approximately 10 percent in the range 320 to 380 nm.

A chemical model is proposed for describing charge-transfer complexes between aromatic amines and electron-accepting benzene derivatives containing a group having a double- or triple-bond conjugated with the benzene ring. According to this model, an electron migrates from the nitrogen atom of the amine to one of the atoms of the multiple-bonded group during charge-transfer interaction. Structure-property relationships were derived for correlating: (1), the transition energies of the complexes; (2), the ionization, or oxidation, potentials of the amines, and (3), the electron affinities or reduction potentials of the electron acceptors, with the electron-donating abilities of the substituents of the various compounds. Transition energies calculated from reported spectroscopic data for these complexes were correlated using equations derived in this study. Similarly correlated were reported data for the above properties of the amine and electron acceptor. Equations were derived for correlating the effect of variation in solvent on the transition energies of the complexes. Correlation of reported spectroscopic data indicated that the greatest effect is caused by variation in the refractive index; of secondary importance was the change in dielectric constant.

New measurements of the vapor pressures and PVT properties of ethane are reported. PVT determinations have been made from near the triple point to 320 K at pressures to 33 MPa. The density range investigated extends to more than three times the critical density. The new measurements of the vapor pressures of ethane extend from 160 K to near the critical point.

The relative enthalpy of solid beryllium aluminate BeO · Al₂O₃ from 1180 to 2025 K and liquid beryllium aluminate from 2170 to 2350 K was measured by "drop" calorimetry using an adiabatic "receiving type" calorimeter. The thermodynamic functions from 1175 to 2025 K and the enthalpy of melting at 2146 K are reported.

The index of refraction and absorptive properties are estimated in nuclear matter consisting of protons and neutrons and in nuclear matter charge neutralized by electrons.

The fluorescence polarization of uniaxial molecules dissolved in an ordered medium is studied. A theoretical model is developed which relates the polarization of the fluorescence emission to molecular structure, orientation of absorption and emission dipole oscillators and the degree of ordering. This theory was tested experimentally using all trans 1,6-diphenyl-1,3,5-hexatriene dissolved in an ordered liquid crystal.

Young's modulus and Poisson's ratio have been measured simultaneously on a series of particulate composites containing volume fractions of filler up to 0.50. The composites consisted of small glass spheres imbedded in a rigid epoxy polymer matrix. The measured values were compared with theoretical values calculated from current theories. A recently generalized and simplified version of van der Poel's theory provided the best agreement. It predicted values of Young's modulus for composites with filler volume fractions up to 0.35. Measured values of Poisson's ratio exhibited scattering, but were consistent with values calculated from van der Poel's theory.

Equations are presented which explicitly express the enhancement of water vapor in CO₂-free air from 0.1 to 2 MPa. The equations are approximations to the formulation of Hyland and provide the means of obtaining enhancement with very modest computational facilities. The agreement with Hyland's enhancement values is well within his estimated uncertainty.