Table 1. Relative Intensities of Pb, I, and Br^a.

	relative intensity (theoretical)	relative intensity (experimental)	normalized intensity (laser off)	relative intensity (laser off)
Pb	1	1	0.89	0.89
I	2.55	2.56	0.91	2.32
Br	0.45	0.44	1.92	0.86

^aTheoretical (from preparation) and experimental (from PES with a photon energy of 540 eV) values before laser illumination. The third column shows the values after 30 min of 0.52 mW laser illumination, normalized to the corresponding intensity before illumination. The fourth column shows the estimated amounts in the surface region compared to the theoretical ratios before illumination (calculated by multiplying the values in column 1 and 3). An increase of the relative amount of halides relative to Pb is found.