Far-infra red RAIRS spectroscopy employing synchrotron radiation as a source, has been used to study the interaction of SnCl4 on a thin-him silica surface. This has been made possible by growing the silica film on a highly reflecting tungsten substrate, enabling the conventional RAIRS geometry to be used. We show that reasonable S/N RAIRS spectra can be obtained in this region, even from films up to 1000 thick, enabling subtle details in the spectrum of the chemisorbed species to be obtained. (C) 1998 Elsevier Science B.V. All rights reserved.Far-infra red RAIRS spectroscopy employing synchrotron radiation as a source, has been used to study the interaction of SnCl4 on a thin-him silica surface. This has been made possible by growing the silica film on a highly reflecting tungsten substrate, enabling the conventional RAIRS geometry to be used. We show that reasonable S/N RAIRS spectra can be obtained in this region, even from films up to 1000 thick, enabling subtle details in the spectrum of the chemisorbed species to be obtained. (C) 1998 Elsevier Science B.V. All rights reserved.