Sum-frequency generation study of reacting species at surfaces

Time-resolved infrared-visible SFG spectroscopy has been used to detect the species produced in chemical reactions: the species produced in the thermal decomposition of fomates on the Ni(111) surface and NiO(111)/Ni(111) surface (details of the latter being described in a separate article in this issue) were detected by inducing a transient temperature jump of similar to 300 K by the irradiation of 1064-nm picosecond pulses. The formates assuming bridged and bidentate configurations as stable species on metal and oxide surfaces, respectively, were found to transform reversibly into a monodentate configuration. The transformation was ascribed to the shift of chemical equilibrium caused by the laser-induced temperature jump at the surfaces. The decomposition started at similar to 25 K and similar to 100 K above the temperatures at which significant transformation occurred on the metal and oxide surfaces, respectively. We postulate that the transformation to the monodentate configuration is a common occurrence in the thermal decomposition of formate on solid surfaces.