Reflection FTIR studies of the conformation of 2,2 '-bipyridine adsorbed at the Au(111) electrode/electrolyte interface

Subtractively normalized interfacial Fourier transform infrared spectroscop y (SNIFTIRS) has been employed to study the conformation of 2,2'-bipyridine (22BPY) adsorbed at the Au(111) electrode surface. in addition, ab initio Hartree-Fock calculations were carried out to calculate the IR spectra for the trans-planar, cis-planar, and twisted conformations both for an isolate d 22BPY molecule and for the molecule attached to a gold atom or ion. The s pectra for the trans- and the cis-conformations were predicted to be distin ctly different. The differences between the predicted spectra and the diffe rences for most structural parameters between the cis-planar conformer and the torsional conformations with a twist of 0 degrees to 40 degrees between the two rings were small. SNIFTIRS spectra with a good signal to-noise rat io were measured only for those potentials where the 22BPY molecules associ ate into stacks. Efficient packing into stacks requires a planar or very ne arly planar conformation for the 22BPY molecules. For these potentials, the SNIFTIRS spectra provided direct evidence that 22BPY molecules coordinated to the surface gold atoms assume a cis- or nearly cis-conformation.