Singlet and triplet states of the CO3 and CO4 molecules

The C-2v isomers of CO2 and CO3 and the metastable D-2d isomer of CO4 are s hown to have a similar electronic nature in both their ground singlet and e xcited triplet states. A simple MO model explaining the electronic structur e of the species containing the cyclic CO2 fragment was suggested. On the b asis of qualitative analysis and the results of MP2/6-31G* calculations, it is shown that the radiationless singlet-triplet decay of the lowest vibrat ional levels of the metastable CO4(1(l)A(l),D-2d) State is hardly probable, but that such a decay seems to be possible in the case of higher-lying vib rational levels of this state. (C) 1999 Elsevier Science B.V. All rights re served.