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Raman spectroscopy due to electric fields at surfaces, which manifests itself as surface-enhanced Raman scattering (SERS) from adsorbate modes, and as electric field-induced Raman scattering (EFIRS) from substrate modes, is discussed. In SERS experiments with benzene adsorbed on small Ni/SiO2 and Pt/SiO2 clusters, using exciting radiation of different wavelengths, we observed not only very strong peaks of the normally Raman active vibrational modes but also normally infrared-active and some inactive modes. Although the frequencies of the modes are only slightly shifted with respect to liquid benzene, the relative intensites of the Raman lines are considerably changed and in addition they are dependent on the excitation wavelength. The observation of metal-carbon vibrations indicates a strong interaction between the adsorbate and the metal atoms. Therefore, in addition to the electric field, a metal-molecule electronic charge transfer may be responsible for the enhancement mechanism. EFIRS is based on the symmetry-forbidden scattering from the longitudinal optical (LO) substrate phonon. It allows the detection of the static electric field in the surface region of semiconductor substrates, which originates from electronic band bending. By EFIRS the band bending can be monitored at surfaces and interfaces for coverages from submonolayer up to more than 100 monolayers, depending on the overlayer material. Here, the Sb/GaAs(110) interface is treated as an example. Considerable band bending dynamics is observed for overlayer thicknesses up to 100 monolayers. Simultaneous analysis of the overlayer structure by Raman scattering from the Sb vibration modes allows the interpretation of the band bending dynamics.

We have used vibrational Raman spectroscopy to study the chemisorption of carbon monoxide and of ethylene, and the chemical interactions of coadsorbed carbon monoxide and hydrogen on silica-supported nickel particles. In each case we observe a strong enhancement of all measured vibrational bands which depends on the excitation wavelength. The maximum enhancement lies always in the excitation wavelength range 5200–4500 A. The enhancement is of the order 102−104. The complex spectra from coadsorbed CO and H2 indicate the formation of several surface species: adsorbed carbon monoxide, hydrocarbon-like species, and different oxygen-containing hydrocarbon compounds. A complete assignment of all vibrational bands is not possible because of the complexity of the Raman spectra.

The Raman spectra of carbon monoxide adsorbed on Raney nickel and on supported SiO2 are measured at high pressures and low temperatures with a rotating cell. In addition to the vibrational bands of adsorbed Ni(CO)4, we find three band systems of CO stretching vibrations at high wavenumbers and several bands at low wavenumbers. The CO stretching vibrations agree with infrared spectra.

Raman spectroscopy was used to characterize the extremely long duration metastable state of Na2[Fe(CN)5NO]·2H2O single crystals. By excitation with light of λ>540 nm only the Raman spectrum of the ground-state configuration is obtained. With an excitation wavelength in the range 540–450 nm, the vibrational bands of the ground- and metastable-state configurations are observed together with approximately equal intensities. In the wavenumber shift range 400–2200 cm−1 for each vibrational mode of the ground state a Raman band is found, but no splitting of degenerate modes appears. It is concluded that the symmetry of the molecule is not changed by pumping the metastable state. Excitation with light of λ=406.7 nm proves the existence of higher energetic states of the metastable configuration, which do not combine with the ground state. In addition to a thermal decay channel, there exists a further channel for depopulation of the metastable state using red light. Absorption spectroscopic measurements show the existence of an excited electronic state at 685 nm in the metastable configuration. This low-lying energy level crosses with the first excited electronic level of the ground-state configuration.

The Raman spectrum of chemisorbed benzene and deuterated benzene has been measured in the frequency range of 200–3400 cm−1 in backscattering geometry. In order to suppress the strong second-order light-scattering spectrum of glass, a difference Raman scattering cell has been developed. The vibrtational bands are shifted only slightly compared with liquid benzene. Additional bands are found, which are symmetry forbidden in free benzene. These bands result from symmetry lowering produced by the site symmetry of the surface. Compared with the Raman spectrum of liquid benzene, the vibrational bands of chemisorbed benzene are strongly enhanced.

The chemisorption of hydrogen on silica-supported nickel has been investigated by Raman spectroscopy at low temperatures. In the spectral range of 200–2500 cm−1, three systems of vibrational bands are detected. The vibrational bands in the high frequency range at 1999 cm−1 and 2030 cm−1 are interpreted as ṽ(NiH) stretching vibrations of a linear chemisorbed species. At 950 cm−1 a weak broad vibrational band is observed, which is assigned to a multibonded surface species. Two vibrational modes in the spectral range of 600–800 cm−1 result from δ(NiH) deformation vibrations of chemisorbed hydrogen. The spectral data are compared with the vibrational spectrum of chemisorbed deuterium.