Volume 26, Issue 5, September 1997
Index of content:
26(1997); http://dx.doi.org/10.1063/1.555999View Description Hide Description
In this compilation we have used data from some 20 references, only two of which were available to C. E. Moore for her 1949 Atomic Energy Levels tables. The new compilation thus includes significant revisions, extensions, and improvements of the earlier data for configurations of the types and and also extends the energy range to higher configurations, including those involving 1 electron excitation. The observed wavelengths for some 200 lines are given with their energy-level classifications. The wavelength measurements, which extend from 89 to 31 780 Å, were obtained from emission spectra of hollow-cathode and arc discharges, beam-foil spectra, and far-ultraviolet photoabsorptionspectra. In addition to the energy levels derived from these spectra, we include levels obtained from multiphoton resonance-ionization mass spectrometry and projectile-Auger spectroscopy. We have evaluated a number of levels by using series formulas and/or theoretical results; these levels are more accurate than values derived from available wavelength measurements. Wavelengths calculated from energy-level differences are given for all lines; these “Ritz” wavelengths are more accurate than the observed values wherever the differences are significant.
26(1997); http://dx.doi.org/10.1063/1.556000View Description Hide Description
A self-consistent, single-valued representation of the major physical, mechanical, and thermal properties of a sintered α-SiC is presented. This comprehensive set of properties is achieved by focusing on a narrowly defined material specification in which boron and carbon are used as sintering aids to produce a dense ceramic (⩾98% of the theoretical maximum density) with a grain size of (6±2) μm. Such a representation is highly desirable in applications of concurrent engineering practices and for the increasing use of electronic processing of product specifications.
26(1997); http://dx.doi.org/10.1063/1.555995View Description Hide Description
In this article, available information on the cross sections and rate coefficients for collisional interactions of dichlorodifluoromethane F with electrons is critically evaluated and synthesized. This gas has many industrial uses and is of atmospheric and environmental interest. The CClF molecule fragments rather extensively under electron impact, principally via dissociativeionization and dissociative attachment; the latter process is temperature dependent. Information is presented and discussed on: (1) electron scattering processes [cross sections for total electron scattering, momentum transfer, differential elastic electron scattering, integral elastic electron scattering, and inelastic electron scattering for rotational and vibrational (direct and indirect) excitation]; (2) electron impactionization (cross sections for total, partial, and double ionization and coefficients for electron impactionization); (3) electron attachment (electron attachment cross sections and rate constants and their energy and temperature dependencies, electron attachment coefficients, dissociative attachment fragment anions, and negative ion states); (4) optical emission under electron impact, and (5) electron transport coefficients (electron drift velocity and ratio of transverse electron diffusion coefficient to electron mobility). Based upon the assessment of published experimental data, recommended values of various cross sections and rate coefficients are generated in graphical and tabular form. Areas where additional data are needed are identified, such as the measurement of the cross sections for momentum transfer and electron impactdissociation of CClF into neutral species.
26(1997); http://dx.doi.org/10.1063/1.556001View Description Hide Description
The biennial review of atomic weight, (E), determinations and other cognate data has resulted in changes for the standard atomic weight of 21 elements. The five most significant changes are: boron from to carbon from to arsenic from to cerium from to and platinum to An annotation for potassium has been changed in the Table of Standard Atomic Weights. To eliminate possible confusion in the reporting of relative lithium isotope-ratio data, the Commission recommends that such data be expressed using ratios and that reporting using ratios be discontinued. Because relative isotope-ratio data for sulfur are commonly being expressed on noncorresponding scales, the Commission recommends that such isotopic data be expressed relative to VCDT (Vienna Cañon Diablo Troilite) on a scale such that of IAEA-S-1 silver sulfide is 0.9997 times that of VCDT. Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on oxygen are included in this article for the information of the interested scientific community.