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Although the theory of photoemission from single-crystalline solids and ordered overlayers has been studied by almost every available theoretical tool, it is quite surprising that there has not yet been any theoretical investigation of photoemission from the disordered condensed phase. In this work, we address this problem. Starting from first principles, we show that the photoelectron angular distribution from the disordered condensed phase is governed by the same general formula as in the gas phase, i.e., by Yang's formula, and in general, is highly anisotropic. This anisotropy in the angular distribution of the photoelectrons has many far reaching consequences. The most important one is that the theoretical expression for the angle-integrated photoemission intensity, which was first derived by Berglund and Spicer, needs to be modified. Another important consequence is the sensitivity of the photoemission intensity to the polarization of the incoming light: we show that at any incident angle, polarized light leads to a higher photoemission intensity than unpolarized light, with the only exception being at normal incidence where both polarized and unpolarized light lead to the same intensity. In this work, we have developed an extremely accurate technique for the measurement of the condensed phase asymmetry parameter (usd\betausd) over all range of photon energies. The behavior of usd\betausd at energies around the Cooper minima has a very important application in surface science. Since in this energy region, the usd\betausd parameter is very sensitive to the nature of the initial states, its measurements can yield information on the hybrid (bandlike) or atomiclike character of d-valence states of a transition metal at its interface with an elemental semiconductor. An important characteristic of this novel technique is its remarkable resolution. Unlike other surface sensitive tools, such as transmission electron microscopy and diffraction or reflection high energy electron diffraction, which have resolutions at coverages well above 10 ML, this technique has resolution at coverages as low as.05 ML, perhaps as good as that of the scanning tunnelling microscopy. Finally in this work, we show that in the condensed phase, the energy dependence of the usd\betausd-parameter at energies near the threshold can yield information about the nature of the continuum waves, i.e., about a quantity which, in general, is very difficult to study experimentally.
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