Infrared study of hydrogen chemisorbed on W(100) by surface-electromagnetic-wave spectroscopy

Abstract

The ${\nu }_1$ vibrational mode of H chemisorbed on W(100) at saturation coverage has been measured at high resolution by infrared surface-electromagnetic-wave (SEW) spectroscopy. This technique is observed to provide an order-of-magnitude larger contrast ratio for weak vibrational modes on metal surfaces than is expected from reflection-absorption spectroscopy. A UHV compatible geometry has been devised so that SEW's can be excited on the W(100) surface with a quasitunable C${\mathrm{O}}_2$ laser. We find that at room temperature the center frequency and absorption strength of the ${\nu }_1$ mode, as measured with SEW's, are in good agreement with electron-energy-loss-spectroscopy measurements. In addition, our high-resolution study leads us to postulate that the ${\nu }_1$ absorption is composed of a sharp zero-phonon line surrounded by broad one-photon sidebands.