Jf. Fan et M. Trenary, SYMMETRY AND THE SURFACE INFRARED SELECTION RULE FOR THE DETERMINATION OF THE STRUCTURE OF MOLECULES ON METAL-SURFACES, Langmuir, 10(10), 1994, pp. 3649-3657
Reflection absorption infrared spectra for several adsorbates on Pt(11
1) are presented that illustrate the use of symmetry in applying the s
urface IR selection rule. The selection rule states that only vibratio
ns that belong to the representation of the surface normal will be sur
face IR active. The selection rule does not forbid vibrations that are
dominated by the stretching of bonds that are parallel to the surface
, and we show two such examples: the O-O stretch of adsorbed Oz and th
e C-C stretch of di-sigma bonded ethylene. Using multilayer CH3I as an
example, we show how IR bands can be split due to formation of struct
ures with symmetry different from the isolated molecule. Spectra of su
bmonolayer coverages of CH3, ICH3, CCH3, and CCD3 demonstrate that, ev
en for adsorbates having the same symmetry and same functional group,
the relative intensities of the allowed vibrations can be quite differ
ent.