Structure of Methyl Pyruvate and α-(1-Naphthyl)ethylamine on Pd(111)

The adsorption of methyl pyruvate and alpha-(1-naphthyl)ethylamine (NEA) on Pd(111) is explored using first-principles density functional theory (DFT) calculations. It is found that methyl pyruvate adsorbs in a flat-lying geometry with a heat of adsorption of similar to 44 kJ/mol, in good agreement with the experimentally measured desorption activation energy of 41 +/- 6 kJ/mol. For a perpendicular methyl pyruvate geometry, the s-cis conformer is the most stable, while previous experimental results suggest that it adsorbs in the s-trans conformer. Since the s-trans conformer is the most stable in the gas phase, this may be due to the formation of a metastable species on the surface. The calculated heat of adsorption (similar to 29 kJ/mol) is in good agreement with the experimental desorption activation energy (33 4 +/- 4 kJ/ mol). NEA adsorbs on Pd(111) predominantly through the naphthyl ring with a heat of adsorption of similar to 224.3 kJ/mol in an exo conformation and 2.1 kJ/mol less stable in an endo conformation. Including effects of van der Waals' interactions in the calculation dramatically increases the adsorption energy (to 563.7 kJ/mol) and slightly increases the energy difference (to 2.8 kJ/mol) but does not affect the order of energies for the two conformers nor does it have a significant effect on their optimized geometries. The B-3u out-of-plane naphthyl C-H bending mode and the NH2 wagging mode (782 and 802 cm(-1)) are not observed for the adsorbed species due to a downward shift in the C-H bending frequencies on adsorption and a change in the orientation of the dynamic dipole moment for the NH2 causing it to be surface infrared forbidden.