Ultraviolet Spectra of Carbon Monoxide

Abstract

The vertical excitation energies for many of the known electronic transitions in carbon monoxide have been calculated from LCAO‐MO SCF functions built on three different basis sets of functions: (a) 1s, 2s, 2s′, 2p, and 2p′ atomic functions on each center; (b) 1s, 2s, 2p, 3s, and 3p atomic functions on each center; (c) 1s, 2s, 2s′, 2p, 2p′, 3s, and 3p functions on each center. The excitation energies calculated from the functions built on set (a) are hardly different from those obtained from an earlier calculation where the SCF orbitals were constructed from the simplest possible basis set (1s, 2s and 2p functions on each center). Set (b) gives results which are in quite good agreement with experiment for all the transitions studied. Our calculations support the analysis made many years ago by Mulliken that the presently known electronic transitions in carbon monoxide can be divided into (1) transitions between molecular orbitals both of which are mainly made up of atomic L functions; (2) transitions between molecular orbitals the lower of which is mainly made up of atomic L functions and the upper is mainly atomic M functions. Set (c) gives the best energy for the ground state and moderately good agreement with experiment for both kinds of transitions.