THEORETICAL-STUDY OF THE LOWEST 5-PI AND 5-SIGMA+ STATES OF CO

The lowest 5PI and 5SIGMA+ states of CO are characterized using very large one-particle basis sets and the internally contracted multireference configuration-interaction treatment of electron correlation. It is found that the (1) 5SIGMA+ state is weakly bound (D(e)=572 cm-1) with an r(e) of 4.76 a0, in good agreement with earlier theoretical calculations by Rosenkrantz et al. [Theor. Chim. Acta 82, 153 (1992)]. The (1)5PI state (hereafter designated a'' 5PI ) has a weakly bound outer well (D(e)=18 cm-1, r(e)=5.80 a0) and a significantly bound inner well (D(e)=6043 cm-1 r(e)=2.76 a0). It is shown that the emission spectrum between about 360 and 520 nm observed by Bahrdt et al. [Chem. Phys. 144, 273 (1990)] can be assigned to the a'' 5PI-a' 3SIGMA+ and a'' 5PI -d3DELTA transitions. Franck-Condon factors are presented to aid in the experimental identification of the a'' 5PI state by absorption from the low-lying triplet states of CO.