Ab initio R-matrix/MQDT method for near-edge x-ray absorption fine structure

Abstract

We have investigated the feasibility of an ab initio polyatomic R-matrix/MQDT (multichannel quantum defect theory) method using Gaussian type basis functions for bound and continuum states to analyze the near edge feature of molecules. Test molecules here are N2, C2H2, and NO. The R-matrix/MQDT method is revealed to be indispensable for the Rydberg states with higher quantum numbers and continuum states, none of which can be described by using Gaussian type functions in the outer region from an appropriate boundary. The close-coupling calculation augmented with the correlation term, which is carried out for the inner region, is powerful to describe the valence states and the interchannel coupling in several core-ionized states.