The profile of the 2140 cm−1solid CO band on different substrates

We have studied the profile of the 2140 cm−1fundamental band of solid carbon monoxide CO at low temperature 10–15 K by infrared transmission spectroscopy and by reflection absorption infrared RAIR spectroscopy. In particular, transmission spectra have been taken after CO had been adsorbed on a bare crystalline silicon substrate and on pre-adsorbed solid N2layers of different thickness. RAIR spectra have been taken after CO had been adsorbed on a bare gold substrate and on pre-adsorbed solid N2layers of different thickness. Laboratory spectra show that the profile of the fundamental CO band at about 2140 cm−1is different in the different instances considered. In particular, we have found that the relative intensity of the LO and TO modes of the CO band depends on the thickness of the N2layer. Here we present the experimental results and show that these can be predicted by the elementary electromagnetic theory.