HEATING AND BREAKING OF AD-MOLECULE BOND BY INELASTIC TUNNELING

A two-mode model is presented to analyze the vibrational excitation of an adsorbed molecule in a scanning tunneling microscope, and to explo re the possibility of breaking the ad-molecule bond by inelastic tunne ling. Non-equilibrium heating between different modes occurs due to th e differences in electron-vibration coupling and in the electronic res onance near the Fermi level. For CO/Cu(100), the stretch mode can be e xcited to a much higher temperature (approximately 1000 K) than the mo lecule-surface mode (approximately 100 K) at a current of 10(-7) A. An harmonic coupling between the two modes leads to energy transfer from the highly excited stretch to the cooler molecule-surface bond, and in fluences the bond-breaking process drastically at the surface.