HIGH-RESOLUTION PHOTOABSORPTION AND PHOTOELECTRON-SPECTRA OF BROMINE-CONTAINIUG MOLECULES AT THE BR 3D EDGE - THE IMPORTANCE OF LIGAND-FIELD SPLITTING

Using monochromatic synchrotron radiation, we have recorded high-resol ution Br 3d photoelectron and photoabsorption spectra (PES and PAS, re spectively) for the five molecules: HBr, DBr, Br-2, CH3Br and CF3Br. T he Br 3d PES of HBr, DBr and Br-2 show five peaks due to the combined effects of ligand field (or molecular field) and spin-orbit splitting. The CH3Br and CF3Br PES are vibrationally broadened, but also show ad ditional broadening from ligand field splitting. The Br 3d ligand fiel d splittings (as quantified by the crystal field C-2(0) parameter) are similar to the I 4d values for the iodine analogues, and increase in the order of CH3Br < HBr, DBr < Br-2 < CF3Br. The Br 3d binding energi es also increase in the above order due to the increasing electronegat ivity of the substituents. The very complex Br 3d photoabsorption spec tra also show the same ligand field/spin-orbit splitting which split e ach (3d(-1)) --> Rydberg transition into five transitions. These spect ra are dominated by the peaks from the five (3d(-1)) --> 5p transition s; but a myriad of other peaks from the (3d(-1)) --> nd (n = 4,5), np (n = 6-9), ns (n = 6,7) and nf (n = 4, 5) transitions are required to fit these spectra. Good fits to all the spectra have been obtained usi ng ligand field splittings which are similar to the PES results, and q uantum defects for s, p, d and f orbitals of similar to 3.3, similar t o 2.6, 1.6-2.0 and 0.8-1, respectively.