15min:

WANG CHEN, JIAN TANG AND KENTAROU KAWAGUCHI, Graduate School of Natural Science and Technology Okayama University, 3-1-1 Tsushima-Naka, Okayama 700-8530, Japan.

The Phillips system and the Ballik-Ramsay system of the spectra of C₂ have been studied extensively before, and the energy difference between the ground X^{1 +}_g state and the first triplet a³ _u state has been determined by analyzing the spin-orbit interaction between the X^{1 +}_g and b^{3 -}_g states. However, the analysis was carried out previously for the individual vibronic bands, and the perturbation parameters SO|v'> of the spin-orbit interaction determined for the different vibronic states lead to the very different values of A_so^bX.^, In the present study, we re-analyzed the previous spectral data^a,, by using the overlap integrals (Franck-Condon factors) and r-centroids between the vibronic states of X^{1 +}_g and b^{3 -}_g calculated from the RKR potential and by fitting all the vibronic states simultaneously. A new set of molecular parameters was obtained, including the single-valued spin-orbit interaction constant A_so^bX=3.067(9) cm^-1 and the energy difference E=719.84(6) cm^-1 between the X^{1 +}_g and a³ _u states, the latter of which is about 1.5 cm^-1 larger than the previously determined value.^a This new result may guide for searching the forbidden transitions between the singlet and triplet states of C₂.