The low-lying excited states of water, methanol, and dimethyl ether

Abstract

Improved virtual orbital (IVO) calculations have been performed on the low-lying excited states of water, methanol, and dimethyl ether using minimal basis sets of contracted gaussian functions augmented with diffuse s and p functions. In all three molecules the low-lying states correspond to excitations out of an oxygen lone pair orbital to an excited orbital having the basic character of a 3s or 3p Rydberg orbital centered on the oxygen. The 3s and 3pb z Rydberg orbitals in water have especially large stabilities (term values) arising from favorable interactions with the electron-deficient hydrogens. Methylation diminishes this added stability in methanol and destroys it in dimethyl ether. The IVO calculations are used to assign the low-lying transitions in the optical and electron impact spectra of methanol and dimethyl ether.