Molecular orbitals photoelectric effect

One of the most direct methods is photoelectron spectroscopy (PES), an adaptation of the photoelectric effect (Section 1.2). A photoelectron spectrometer (see illustration below) contains a source of high-frequency, short-wavelength radiation. Ultraviolet radiation is used most often for molecules, but x-rays are used to explore orbitals buried deeply inside solids. Photons in both frequency ranges have so much energy that they can eject electrons from the molecular orbitals they occupy. 

Einstein s explanation of the photoelectric effect was not his only contribution to chemistry. His Ph.D. dissertation, submitted in 1905, was entitled A New Determination of Molecular Dimensions. His investigation of Brownian motion (the random movement of microscopic particles suspended in liquids or gases) was intended to establish the existence of atoms as being indispensable to an explanation of the molecular-kinetic theory of heat. And the concept of relativity has shed light on the motions of electrons in the core orbitals of heavy elements, see also Quantum Chemistry. 

It is well known that the fine structure of the K absorption edge arises fiom the photoelectric effect of a Is orbital electron of an absorption atom. It is obvious that the peaks in the rising part on XANES spectra are ascribed to the electron transition fiom an inner shell orbital to higher molecular orbitals (called as Is electron transition in this rqrort). Therefore, to estimate the probabilities of the Is electron transition by an electronic dipole theory, theoretical XANES spectrum can be caloilated using molecular orbital calculations. ... 

This equation is simply that for the photoelectric effect initially observed for emission from metallic surfaces, except that the work function term has been replaced by the energy required to remove an electron, i.e., the ionization potential. Such measurements allow the construction of molecular orbital energy diagrams directly from experimental data and provide a way of critically examining bonding theories without recourse to intuition. 

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