DFG (DE 2366/1)

Theoretical description of the electron continuum spectrum in molecules is a very complex and challenging problem. Here, the main difficulties are connected both with the noncentral potential of a molecule and with the essentially delocalized character of continuum orbitals. Therefore, general methodologies developed for atoms and standard quantum chemistry methods available for molecules are unfit, and the problem is difficult or even impossible to attack in a conventional way. In the past decades, considerable efforts have been invested to the development of advanced nonstandard approaches to solve the electron continuum problem in molecules. Nevertheless, most of the new methods developed for polyatomics are restricted to the calculation of the total excitation and decay spectra and are not designed for the description of the partial spectra. Moreover, nearly all of the available methods are unable to provide an accurate theoretical description of the partial electron continuous waves with given angular momentum quantum numbers, which are required for studying angular-resolved excitation and decay spectra. Nowadays, the latter problem is elaborated only for linear molecules. The principal investigator has also contributed to the development of such a method for diatomics, which is known as the single center (SC) method and is a powerful tool for angular-resolved ionization studies of molecules.

The proposed project aims at providing accurate and reliable theoretical description of the electron continuum spectrum in nonlinear polyatomic molecules and considering key investigations. We plan to apply the SC method to the description of partial electron continuous waves in polyatomics. The developed approach will be implemented in a computer code. This will result in an accurate and stable numerical tool for the theoretical study of angular-resolved photoabsorption problems of polyatomics. We, first, plan to test the method and code by considering total and partial excitation and decay spectra of relatively small polyatomics consisting of a few atoms, and to compare our results with the most accurate theoretical and experimental data available in the literature. Afterwards, the method will be applied to investigate larger molecules and, simultaneously, angular-resolved spectra. In the first case, we will mainly concentrate on the photoionization of small alkali metallic clusters. In the second case, we will consider applications to the angular-resolved electron spectra of polyatomics, available in the literature. We finally plan to describe new angular-resolved experiments on electron and fluorescence emission in polyatomics performed by our cooperation partners. Applications to large molecules and clusters is our perspective aim, which can only be realized on the basis of the investigations proposed within this project.