Abstract
The ability to study the interactions of hydrocarbons on carbon surfaces is an integral step towards
gaining a molecular level understanding of the chemical reactions and physical properties occurring on
them. Here, we apply vibrational sum frequency generation (SFG) to determine the tilt angle of toluene, a common organic solvent, on mm-thick highly oriented pyrolytic graphite (HOPG). The combination of a time-delay technique, which results in the successful suppression of the nonresonant SFG response, and a null angle method is shown to overcome the ’strong optical absorber’ problem posed by macroscopically thick carbon samples and yields a molecular tilt angle of toluene in the range of 37° to 42° degrees from surface normal. The implications of this approach for determining the orientation of organic species adsorbed on carbon interfaces important for energy relevant processes are discussed.