Theoretical study of the Cl 1s and 2p near edge photoabsorption spectra of HCl by accurate ab-initio configuration interaction and density functional approaches Original Research Article

Calculations of the discrete Cl 1s and 2p excitation spectra of HCl are performed employing accurate ab-initio Configuration Interaction (CI) and Density Functional (DF) approaches. The core excited spectra above edge are described with a new DF method based on a one-centre approximation. The highly correlated quasi-degenerate perturbation scheme gives results in excellent accord with experimental data and allows a definite assignment of the Rydberg excited states below edge. The simpler 1h–1p CI scheme shows some deficiencies essentially attributed to the use of inadequate orbitals, although it appears adequate for a qualitative description of the spectra. The DF approach provides dependable results for the lower-energy states of the discrete spectra while some limitations affect the present description of the higher Rydberg states. Good agreement with experimental data is obtained for the calculated cross-section profiles relative to the Cl 1s and 2p photoionization. Also the theoretical asymmetry parameter profiles are analysed.