Reflection-absorption spectroscopy in the ultraviolet (UV) of C6H6 molecules physisorbed on a gold surface has been observed in a single-pass experiment for the electronic transition (1)A(1g) --> B-1(2u) near 250 nm. The linewidths of transitions in this electronic band are 160 cm(-1). This technique permits the detection of a very low density of molecules physisorbed on a surface.