Systematic study of molecular anions within the self-consistent-field approximation: OH−, CN−, C2H−, NH−2, and CH−3

Abstract

The title molecular anions have been studied at the self-consistent-field (SCF) level of theory with several different basis sets. The smallest of these bases is triple zeta (TZ) in quality while the largest can be labeled near Hartree–Fock limit. The dependence of proton affinities, dipole moments, harmonic frequencies, and infrared intensities on the inclusion of diffuse functions in the basis set is investigated. It is concluded that at the SCF level of theory the addition of diffuse s and p functions (for first row elements) is necessary in order to obtain reliable results. This is true especially for NH−2 and CH−3. A method to extend any standard Gaussian basis set is suggested. Finally, predictions are made for some of the as yet unobserved fundamentals of the anions.