Necessity of relativistic dipole selection rules in photoemission: A reply

We have calculated normal photoemission spectra of Cu(110) for both spin-orbit interaction neglected and included. Our results show that the occurrence of a nonrelativistically forbidden transition of type ${\Sigma }_2\to {\Sigma }_1$ in recent experimental photoemission data of Goldmann et al. is primarily a relativistic effect. It is related to a relaxation of the nonrelativistic dipole selection rules which is caused by spin-orbit interaction. Our results prove that in photoemission relativistic effects may be important even for elements of low atomic number and may dominate effects due to finite instrumental resolution.