The vertical excitation energies for many of the known electronic transitions in carbon monoxide have been calculated from LCAOhyphen;MO SCF functions built on three different basis sets of functions: (a) 1s, 2s, 2sprime;, 2p, and 2pprime; atomic functions on each center; (b) 1s, 2s, 2p, 3s, and 3patomic functions on each center; (c) 1s, 2s, 2sprime;, 2p, 2pprime;, 3s, and 3pfunctions 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, 2sand 2pfunctions 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 atomicLfunctions; (2) transitions between molecular orbitals the lower of which is mainly made up of atomicLfunctions and the upper is mainly atomicMfunctions. Set (c) gives the best energy for the ground state and moderately good agreement with experiment for both kinds of transitions.
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