SPECTROSCOPIC AND KINETIC-STUDIES OF FORMIC-ACID ADSORPTION ON CU(110)

The adsorption of formic acid on Cu(110) has been studied using Fourie r-transform reflection/absorption IR spectroscopy (FTRAIRS) and molecu lar beam measurements. The adsorption is inefficient at 300 K, having an initial sticking coefficient (S-0) of ca. 0.1. Experiments with sub -ambient crystal temperatures show much more efficient adsorption with S, being 0.9 at 180 K. The adsorption appears to be of the precursor type. FTRAIRS indicates that the species adsorbed at 200 K is very dif ferent from that at 300 K. The latter is the usually reported bidentat e formate with a simple IR spectrum and symmetrically equivalent oxyge ns. At 200 K we propose that formate is produced in the monodentate fo rm, that is strongly anchored to the surface through one oxygen, with the other in the form of a carbonyl group. However, the carbonyl group may also be bonding to the surface weakly. The monodentate species co nverts to bidentate upon heating. If the bidentate formate is cooled t o 200 K, formic acid can be adsorbed from the gas phase and this conve rts all the formate on the surface back to the monodentate form.