Dj. Dai et Ge. Ewing, VIBRATIONAL OVERTONE SPECTROSCOPY AND COUPLING EFFECTS IN MONOLAYER CO ON NACL(100), Surface science, 312(1-2), 1994, pp. 239-249
Monolayer physisorbed CO on NaCl(100) single crystal surfaces has been
investigated with polarized Fourier transform infrared (FTIR) spectro
scopy at 5 K. While the fundamental (upsilon = 1 <-- upsilon = 0) tran
sition of the monolayer has been studied previously, we report for the
first time the overtone (upsilon = 2 <-- upsilon = 0) transition. Its
integrated absorbance is very weak, being only 0.5% of the fundamenta
l. Comparisons of the transition frequencies, the bandwidths and absor
bances for these two transitions together with those of dilute isotope
s allow us to isolate the contribution of dynamic and static coupling
effects of molecules within the monolayer. We can also distinguish hom
ogeneous and heterogeneous effects from band profiles of these various
transitions. The method of analysis of these data is the exciton mode
l appropriate to treating the coupling of the electric multipoles of m
olecules within the adlayer.