REFLECTION-ABSORPTION IR SPECTROSCOPY AT CRYOGENIC TEMPERATURES

Reflection-absorption IR spectroscopy (RAIRS) has been used to study t he adsorption and behaviour of a number of adsorbates on a Cu(100) sur face at cryogenic temperatures (in the range ca. 20-77 K). Sample cool ing to temperatures below 77 K presents a wide range of opportunities for definitive experiments on the nature of the surface-adsorbate and adsorbate-adsorbate interactions. Adsorption of methane and carbon dio xide on Cu(100) at 24 K results in physisorbed mono- and multi-layers; for CO2 the effect of orientation of the layer can be clearly seen. C arbon monoxide adsorption on Cu(100) produces both chemisorbed and phy sisorbed molecules. The physisorbed multilayers are desorbed at 26 K, leaving chemisorbed and physisorbed monolayers. Above 35 K, a transiti on occurs where the physisorbed species disappears and additional CO i s chemisorbed. The final example is the use of an argon matrix to dilu te the adsorbate and disrupt adsorbate-adsorbate interactions, for ads orbed chromium hexacarbonyl on copper.