Sensitivity improvement in surface infrared spectroscopy: Design, characteristics, and application of a high-temperature graphite source

An infrared source designed to increase the sensitivity of the technique of reflection absorption infrared spectroscopy (RAIRS) for the detection of molecular adsorbates at submonolayer coverages on metal surfaces is described. The source is based on a graphite element with a lifetime of 500 h when operated at a temperature of similar to2300 K in a static pressure of 800 Torr of argon. The design allows for rapid and easy replacement of the low cost graphite element. The signal-to-noise ratio (SNR) achieved with this source for spectra obtained with both mercury cadmium telluride and indium antimonide detectors is a factor of 3-higher than obtained with a standard silicon carbide (SiC) source operated at similar to1500 K. With the higher SNR available with the graphite source it was possible to detect two vibrational features, delta(s)(CH3) of methyl at 1247 cm(-1), and nu(CH) of methylidyne at 2956 cm(-1), that were not detected in previous RAIRS studies. (C) 2004 American Institute of Physics.