Effect of Electronegativity and Polarizability on the C 1s Core Ionization Energies of Halomethanes

The charge and relaxation effects on the C 1s core ionization energies of halomethanes CHnY4-n-mZm (Y, Z=F, Cl, Br, I) were evaluated based on the atomic electronegativity χP and the polarizability α. The charge effect was scaled using the electronegativity discrepancy between C and H or the halogen atom in the CH or CY(Z) bond. The relaxation effect (induced dipole) was scaled using the charge on the carbon atom together with the polarizabiliy of the H and halogen atoms. Furthermore, the electrostatic-relaxation shielding ΔSi of the C 1s electron in the halomethane was expressed by the charge effect in combination with the relaxation effect. By introducing the ΔSi into the Slater model, a Slater-like model was obtained for calculating the C 1s core ionization energy E1,C of halomethane, whose correlation coefficient r is 0.99987, and the average absolute error is only 0.038 eV between the calculated and the experimental C 1s core ionization energies for 27 halomethanes. Moreover, the cross-correlation was tested using the leave-one-out (LOO) cross-validation method, and the obtained model has good predictive ability and stability (the correlation coefficient rcv was 0.99977, and the average absolute error between the predicted and the experimental values is only 0.049 eV). The proposed model probably lays a good foundation for computing the core ionization energies of various atoms in more complex molecules.