THE CONCENTRATION-DEPTH PROFILE AT THE SURFACE OF A SOLUTION OF TETRABUTYLAMMONIUM IODIDE IN FORMAMIDE, BASED ON ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY

We have investigated a solution of tetrabutylammonium iodide (TBAI) in the polar solvent formamide (FA) using angle-resolved photoelectron spectroscopy at the Berlin Electron Storage Ring for Synchrotron Radiation (BESSY). The concentration was set to 0.5 molality. We have evaluated the signals from C 1s pertaining to TBAI and FA separately, varying the photon energy between 310 and 540 eV as well as the e-emission angle with respect to the surface normal. The combination of these data with earlier results from ARXPS Obtained by Siegbahn and co-workers allowed us to establish a concentration-depth profile of the surface-active salt TBAI. For this purpose we have employed a new theoretical formulation and developed a new elaborate fitting program based on a genetic algorithm. The concentration of the salt could be followed down to a depth of about 45 Angstrom below the surface. Cross sections for the inelastic energy loss of electrons in the liquid could be established as a function of electron energy. Comparison with conventional surface tension measurements allowed us to derive absolute values for the cross sections.