Orientation of carboxylates on TiO2(110)

C K-edge NEXAFS has been used to examine the orientation of formate. acetat e and propanate in their 2 x 1 overlayers on TiO2(1 1 0) at 300 K. These da ta indicate that the carboxylate planes are more or less perpendicular to t he surface. The off-normal tilt angles from NEXAFS are 20 +/- 10 degrees, 0 +/- 5 degrees and 14 +/- 10 degrees for formate, acetate and propanate, re spectively. The corresponding apparent twist angles out of the [0 0 1] azim uth are 29 +/- 10 degrees. 26 +/- 5 degrees and 39 +/- 10 degrees, indicati ng a bond geometry essentially independent of the alkyl chain length. The a pparent twist angles probably arise from averaging of majority and minority species. (C) 2001 Elsevier Science B.V. All rights reserved.