Electron-impact cross sections for Cu atoms

Relative differential electron-impact cross sections have been measured for elastic scattering for excitation of the 3d 10 4p 2 P 1/2,3/2 , 3d 9 4s 2 2 D 5/2 and 3d 9 4s 2 2 D 3/2 states of Cu at 6, 10, 20, 60 and 100 eV in the 0 degrees to 140 degrees angular range. The relative values were normalised to the absolute scale by utilising He as a secondary standard for determining the correct energy dependence and by accepting the value of the calculated elastic differential cross section at 100 eV, 40 degrees as 1.28*10 -16 cm 2 sr -1 . Integral and momentum-transfer cross sections have been obtained by extrapolation to 180 degress. The cross section for the excitation of the 2 P state is large compared to that for elastic scattering, and population inversion in this state with respect to the 2 D state is readily achieved by electron impact. None of the theoretical predictions utilising classical, Born or static-exchange approximations agree with the experimental results at low impact energies.