MO Calculations of the Rydberg Transitions of the Methane Molecule

Abstract

Abstract The vertical transition energies of both the Rydberg and valence-shell type transitions of CH4 were calculated by the use of the ab initio SC-LCAO-MO method. We used Slater-type AO’s as the basis AO’s and added the extra-valence AO’s (3s, 3p, 4s, and 4p) of a carbon atom to the minimal-basis set in order to express the Rydberg MO’s. From the limited CI calculations, the mixing expressed in terms of the orthogonalized AO’s between the Rydberg and valence-shell transitions was shown to be little. The lowest two absorption bands near 9.7 and 11.7 eV were identified as a 3s-like Rydberg transition with a 3p-like one and a 4s-like Rydberg transition with a 4p-like one respectively. The total energy and Mulliken population analysis were also calculated and compared with the results of the minimal-basis calculations.