ELECTRON-IMPACT EXCITATION OF THE (... 6S6P P-1(1)) LEVEL IN YTTERBIUM

We have measured and calculated differential cross sections for electr on-impact excitation of the (...6s6p P-1(1)) level in ytterbium at col lision energies of 5, 10, 20, 40 and 80 eV. Calculations were made in the unitarized distorted-wave approximation. Measurements of the relat ive differential cross section, taking account of volume correction ef fects, were placed on an absolute scale by normalization to the theore tical integral cross section at 80 eV with extrapolation to lower ener gies based on the measured excitation function of Shimon et al (1981 O pt. Spektrosk. 50 571). Excellent agreement between theory and experim ent is obtained in the regime of low momentum transfer.