Strong electronic transitions reflectance spectroscopy

Reflectance. Both internal and external reflectance spectroscopy are relatively simple experiments to perform. Commercially available attachments for standard UV-visible spectrometers can be used. For films with strong electronic transitions reasonable spectra can be obtained. The theory for external and internal reflectance is the same as that for the IR and can be found elsewhere (2, 37). The techniques have not been very popular in their applications to surface analysis. The major reason appears to be... 

RAIRS spectra contain absorption band structures related to electronic transitions and vibrations of the bulk, the surface, or adsorbed molecules. In reflectance spectroscopy the ahsorhance is usually determined hy calculating -log(Rs/Ro), where Rs represents the reflectance from the adsorhate-covered substrate and Rq is the reflectance from the bare substrate. For thin films with strong dipole oscillators, the Berre-man effect, which can lead to an additional feature in the reflectance spectrum, must also be considered (Sect. 4.9 Ellipsometry). The frequencies, intensities, full widths at half maximum, and band line-shapes in the absorption spectrum yield information about adsorption states, chemical environment, ordering effects, and vibrational coupling. 

The absorption spectra of blue copper proteins typically include one major peak and two other peaks of varying size in the range 10,000-30,000 cm-1 (164-166). MCD spectroscopy has proved useful in assigning these peaks. The electronic excitations of the active site can be classed as either d—>d or LMCT transitions. The d- fd transitions will involve excited states where the electron hole remains on the Cu atom while the LMCT transitions will move the hole to the ligands, in particular the sulfur atoms of the Met and Cys groups. Thus the d- d transitions would be expected to be more strongly influenced by spin-orbit coupling and this should be reflected in the relative size of the Cj/Dj ratios of the bands in their MCD spectra. 

Photoelectron spectroscopy is a powerful technique to study ionic and electronically excited levels of atoms and molecules. In the case of single photon excitation of cold molecules the photoelectron spectrum reflects the internal energy levels of the ionic system. Many experiments are performed via two photon ionization enhanced by a one-photon resonance (R2PE spectroscopy) in which transitions to intermediate electronic levels are accessed which strongly enhance the ion yield. Photoelectron spectroscopy of molecules inside superfluid helium droplets is of particular interest since the interaction of free electrons with liquid helium is known to be highly repulsive, so much so that the electrons form bubbles of about 34 A diameter. In this section, three recent photoelectron spectra will be discussed those of bare helium droplets, of Ags clusters and of single aniline molecules in helium droplets. 

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