Quantitative local structure determination of R , R - tartaric acid on Cu ( 110 ) : monotartrate and bitartrate phases

The local adsorption site of the monotartrate and bitartrate species of R,R-tartaric acid deposited on Cu(110) have been determined by scanned-energy mode photoelectron diffraction (PhD). In the monotartrate phase the molecule is found to adsorb upright through the O atoms of the single deprotonated carboxylic acid (carboxylate) group, which are located in different off-atop sites with associated Cu-O bondlengths of 1.92±0.08Å and 1.93±0.06Å; the plane of the carboxylate group tilted is by 17±6° off the surface normal. The bitartrate species adopts a ‘lying down’ orientation, bonding to the surface through all four O atoms of the two carboxylate groups, also in off-atop sites. Three slightly different models give comparably good fits to the PhD data, but only one of these is similar to that predicted by earlier density functional theory calculations. This model is found to have Cu-O bondlengths of 1.93±0.08Å and 1.95±0.08Å, while the planes of the carboxylate groups are tilted by 38±6° from the surface normal.