Wavelength, energy shape, and structure of the Cu Kα1 x-ray emission line

The shape of the Cu Kα1 x-ray emission line was measured with the use of a channeled silicon monolithic double-crystal spectrometer of a novel design. With an accuracy <1%, the only structure detected was a very small shoulder 2.6 eV away from the peak on the low-energy side of it. Values obtained of the full width at half maximum and the index of asymmetry of the line are in good agreement with some of the previously published data. The high stability and accuracy of the spectrometer is demonstrated by the determination of the absolute wavelength of the Cu Kα1 x-ray emission line. The result obtained is λ(Cu Kα1)=1.540 595 2 A (0.85 ppm) on the x-ray scale defined by the National Bureau of Standards value for the lattice spacing of silicon [R. D. Deslattes, E. G. Kessler, W. C. Sauder, and A. Henins, Ann. Phys. (N. Y.) 129 378 (1980)]. A full discussion of the method is given, and ways of increasing the present accuracy by an order of magnitude are indicated. An analysis of the data within the framework of the manybody theory of photoelectron and x-ray emission spectra is presented. The analysis indicates that while a well-defined value for the lifetime width of the core-hole state can be extracted from the data, this is not the case for the asymmetry parameter. The reasons for this behavior are fully discussed. Finally, a value of 1.73 eV is calculated from the data for the width of the Cu K level.