Photoelectron spectroscopic studies of polyatomic molecules. I. Theory

A general expression for the angular distribution of electrons ejected in photoionization of oriented polyatomic molecules is derived. The ionization amplitude is shown to reduce to a sum of terms characterized by the irreducible representations (IRs) of the point group of the (e + M+) system, where M+ is the residual ion of the target M. This derivation automatically yields the angular distribution of electrons ejected in photoionization of freely rotating polyatomic molecules. From the expressions derived here, it is shown how the IR of a photoelectron's continuum orbital for which the dipole amplitudes will not vanish identically can be determined in certain approximations. The photoionization in a bound orbital belonging to the a1 IR of a Td molecule is analyzed, the photoionization amplitude and photoelectron angular distribution are calculated, and the angle-resolved photoelectron spectroscopy of CF4, CCl4, SiCl4, and GeCl4 is discussed.