CRITICAL-POINT ENERGIES FROM INVERSE PHOTOEMISSION SPECTRA OF CU(110) AND NI(110)

Constant initial state (CIS) inverse photoemission measurements of a direct optical transition along the GAMMA ( SUMMATN )K(S) X line in Cu and Ni are presented. From the intensity variation of the emission as a function of the initial state energy the critical point energies X//6// plus //(//1//) equals (22. 6 plus or minus 0. 5)eV, X//6// minus //(//4// prime //) equals (2. 9 plus or minus 0. 3)eV for Ni and X//6// plus //(//1//) equals (19. 7 plus or minus 0. 5)eV, X//6// minus //(//4// prime //) equals (2. 3 plus or minus 0. 3)eV for Cu are determined. These data are in good agreement with recent calculations.