Electron-impact excitation of the (... 6s6p 1P1) level in ytterbium

We have measured and calculated differential cross sections for electron-impact excitation of the (...6s6p P-1(1)) level in ytterbium at collision energies of 5, 10, 20, 40 and 80 eV. Calculations were made in the unitarized distorted-wave approximation. Measurements of the relative differential cross section, taking account of volume correction effects, were placed on an absolute scale by normalization to the theoretical integral cross section at 80 eV with extrapolation to lower energies based on the measured excitation function of Shimon et al (1981 Opt. Spektrosk. 50 571). Excellent agreement between theory and experiment is obtained in the regime of low momentum transfer.