Gauche-trans conformational changes in ethyl formate chemisorbed on Ni(111): Coverage-dependent RAIRS spectra

Infrared reflectance spectra of ethyl formate on Ni(111) at 105 K were reco rded as a function of surface coverage. The RAIRS activities of several ban ds are found to vary in a correlated manner as a function of coverage. The activity of both the asymmetric stretching vibration and the twisting vibra tion of the CH2 group at low coverages conclusively show that adsorption oc curs initially in the s-cis,gauche conformation. These two bands fade out o n increasing the coverage and are completely removed at full monolayer cove rage. The coverage dependence is interpreted in terms of rotational isomeri zation to a planar conformation as the packing density in the adlayer is in creased. The results are consistent with an attribution of the full coverag e molecular structure to the s-trans,trans conformation.