High resolution absorption spectrum of CO2 between 1750 and 2000 Å.: 2.: Rotational analysis of two parallel-type bands assigned to the lowest electronic transition 13B2←(X)over-tilde1Σg+

The absorption spectrum of CO2 gas between 175 and 200 nm was photographed at high resolution some years ago. This very weak spectral region proved to be extremely rich in bands showing rotational fine structure. In Part I [C. Cossart-Magos, F. Launay, J. E. Parkin, Mol. Ph, Vs., 75, 835 (1992), nine perpendicular-type bands were assigned to the lowest singlet-singlet transition, 1 (1)A(2) <-- X(1)Sigma(g)(+) a forbidden transition rendered vibronically allowed by excitation of one quantum of the asymmetric stretching v'(3) (b(2)) vibration. Here, the parallel-type bands observed at 185.7 and 175.6 nm are assigned to the lowest triplet-singlet transition, 13 B, <-- <(X)over tilde> Sigma(g)(+) excited with different quanta of the bending v'(2) (a(1)) vibration. The assignment and the rotational and spin constant values obtained are discussed in relation to previous experimental data and ab initio calculation results on the lowest excited states of CO,. The actual role of the 1(3)B(2), state in CO2 photodissociation, O(P-3)+CO(X (1)Sigma(+)) recombination, and O(D-1) emission quenching by CO(X) molecules is reviewed.