Coupled Cluster Study Of The X-Ray Absorption Spectra Of Formaldehyde Derivatives At The Oxygen, Carbon, And Fluorine K-Edges

We have investigated the performance of a core-valence separated scheme within the coupled cluster (CC) hierarchy of methods CC singles (CCS), CC singles and approximate doubles (CC2), and CC singles and doubles (CCSD) in reproducing the K-edge x-ray absorption spectra of the low-Z elements carbon, oxygen, and fluorine in formaldehyde (CH2O), carbonyl fluoride (CF2O), formyl fluoride (CHFO), and formic acid (CHOOH). The analysis covers the entire frequency region from the first 1s -> pi* excitation to the core-ionization limit, encompassing the region of Rydberg transitions. Moreover, a simulation of the vibronic progressions in the 1s -> pi* bands of both carbon and oxygen in formaldehyde has been performed at the core-valence separated CCSD level, and the results are critically compared with highly resolved experimental data for this molecule. Published under license by AIP Publishing.