Determination of Carbon 1s Core Ionization Energies in Saturated Molecules

Abstract

The Slater-like model was established to calculate the carbon 1s core ionization energies in saturated molecules. Using the atomic Electron Affinity (EA), average valence-shell electron energy EI and polarizability α as parameters, the charge effect, the relaxation effect, and the electrostatic field effect were evaluated for the C 1s core ionization energies in saturated molecules. The charge effect was scaled by electronegativity difference (the difference in EA and the difference in EI between the carbon atom that is being ionized and its adjacent atoms). The relaxation effect (induced dipole) was scaled by the charge on the ionized carbon atom together with the polarizability of all other atoms in the molecules. The electrostatic field effect was scaled using the charges of the other atoms in molecular backbone divided by the distance between the ionized carbon atom and the other backbone atom. Furthermore, the electrostatic relaxation effect ΔSi of C 1s electron was expressed by the above three effects. By introducing the ΔSi into the Slater model, a Slater-like model was obtained to calculate the C 1s core ionization energy E1,C of halomethane and more complex molecules, whose correlation coefficient r is 0.99955 and the average absolute error between the calculated and the experimental values for 63 compounds is only 0.079 eV. Also the crosscorrelation was tested by the Leave-One-Out (LOO) crossvalidation method, and the correlation coefficient rcv=0.99941 and an average absolute error of 0.091 eV between the predicted and the experimental values were obtained. Using the obtained model, some C 1s electron ionization energies were predicted, and the results were in agreement with the experimental values. Application of the developed approach to other systems was also tested.