The inner valence photoionization of acetylene

Abstract

We performed both single and coupled-channel scattering calculations of the photoionization of acetylene using an iterative Schwinger variational method. A comparison of the resulting single-channel and multichannel cross sections shows that the two results differ at photon energies of up to several hundred eV, which indicates that interchannel coupling and/or nonorthogonality terms may continue to be important even at these high photon energies. We compared the energy dependent satellite branching ratios with the corresponding ratios of spectroscopic intensity factors (SIFs) and found that the theoretically predicted high energy convergence of the former to the latter occurs by 1000 eV in only half of the cases studied. When the satellite provenance results from more than one main line, we do not observe this convergence behavior. We compare our theoretical results to experimental synchrotron radiation photoelectron spectroscopy (SRPES) results and illustrate how the superposition of one or more low intensity satellite lines may lead to the erroneous identification of convergence behavior. Based on our theoretical results for the photon energy dependence of the branching ratios of the four principle satellites of acetylene, results which are in excellent agreement with the experimental results, we conclude that all four of the satellites are dynamically correlated according to a phenomenological classification system. This conclusion opposes conclusions of a recent study that three of the satellites are intrinsically correlated, conclusions based upon the same experimental data that we use here, the same classification system, but differing in that the conclusion was formed in part on the basis of SIFs, i.e., static theoretical results. The results presented here underscore the difficulties inherent in analyzing the dynamics of photoionization using static theoretical results such as SIFs, and illustrate how a dynamic theory of photoionization can be used to interpret experimental data.