Wavelength calibration of the CI line at 94.5 nm for comparison with quasar data

With the use of an ultra-narrow-band extreme ultraviolet laser source, tunable near 94 nm, transition wavelengths are determined for lines connecting the 1s22s22p2 P0,1,23 ground-term levels to the 1s22s2p3 S13 excited level in neutral carbon at an absolute accuracy of 4×10-8. With the determination of the zero-velocity rest-frame wavelengths these lines can be included in an analysis of a possible temporal variation of the fine-structure constant α from a comparison with quasar data. A value for the C12/C13 transition isotope shift was also obtained yielding 0.5107(13)cm-1, in average over the three fine-structure lines. The latter measurement will allow to study isotopic evolution in the universe and test models of nuclear processes in stars. © 2005 The American Physical Society.