SINGLE-MOLECULE VIBRATIONAL SPECTROSCOPY AND MICROSCOPY

Vibrational spectra for a single molecule adsorbed on a solid surface have been obtained with a scanning tunneling microscope (STM). Inelast ic electron tunneling spectra for an isolated acetylene (C2H2) molecul e adsorbed on the copper (100) surface showed an increase in the tunne ling conductance at 358 millivolts, resulting from excitation of the C -H stretch mode. An isotopic shift to 266 millivolts was observed for deuterated acetylene (C2D2). Vibrational microscopy from spatial imagi ng of the inelastic tunneling channels yielded additional data to furt her distinguish and characterize the two isotopes. Single-molecule vib rational analysis should lead to better understanding and control of s urface chemistry at the atomic level.