Low frequency infrared emission spectroscopy of molecules at single crystal surfaces

We have developed an infrared emission spectrometer for studying molecules at surfaces in the low frequency spectral region (100–600 cm−1). Here we report on thermal emission (TE) studies of C6D6 and CO on single crystal platinum surfaces. For an exposure of 33 L C6D6 on Pt(1 1 0), we observed an emission peak at 510 cm−1 at temperatures of 90 K up to multilayer desorption, corresponding to an intramolecular out-of-plane bending mode of C6D6. We also studied the adsorbate–substrate stretching vibration for atop CO on Pt(1 1 1) and Pt(1 1 0). At saturation coverage and 200 K, the Pt–C stretch was observed at 466 cm−1 on the Pt(1 1 1) surface, in agreement with previously reported results. On the Pt(1 1 0) surface, the Pt–C stretch was observed at 466 cm−1 on the (1×2) phase and was found to shift upwards to 475 cm−1 on the (1×1) phase. These TE studies demonstrate the capabilities of our instrument in studying low frequency vibrational modes of adsorbed molecules. The possibility of extending the instrument to the study of dynamic surface processes is also discussed.