ADSORBATE VIBRATIONAL DYNAMICS IN THE ANOMALOUS SKIN-EFFECT FREQUENCY REGION

It is shown that in surface infrared reflectance at low frequencies, dipole forbidden parallel adsorbate vibrations give rise to anti-absorption resonances, whose asymmetry is independent of the nature of the adsorbate-substrate bond. The theory is compared with new absolute IR measurements for CO/Cu(100) and (111) over the frequency range 180-2500 cm-1 at high resolution (1 cm-1). The linewidth of the CO frustrated rotation is dominated by energy relaxation via electron-hole pair exitations. The deduced lifetimes (approximately 1 ps) are in good agreement with theory.