Eldad Herceg

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 ∼2300 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 ∼1500 K. With the higher SNR available with the graphite source it was possible to detect two vibrational features, δs(CH3) of methyl at 1247 cm–1, and ν(CH) of methylidyne at 2956 cm–1, that were not detected in previous RAIRS studies.

Comparison of experimental and calculated infrared spectra of aminocarbynes on the Pt(111) surface

Infrared spectra of the three aminocarbynes CNH2, CNHCH3, and CN(CH3)2 attached to Pt, Pt7H6, Pt2, Pt9H14, and Pt4 clusters are calculated from density functional theory and compared with the corresponding experimental spectra measured on the Pt(111) surface. The different clusters provide models for adsorption at on-top, twofold bridge, and threefold bridge sites. For the Pt2 and Pt9H14 models of the twofold bridge site, the calculations successfully reproduce the observed frequency shifts for 13C, 15N, and D substitutions and yield fair agreement with the observed relative intensities. In the case of CNHCH3, the calculations for one of two possible conformers give better agreement with the experimental spectra. No improvement was achieved with the larger Pt9H14 cluster compared with the Pt2 model, indicating that the differences between the experimental and calculated spectra for the latter cluster were not due to finite cluster size effects. The calculated spectra for the different adsorption site mode...