ELECTRON SPIN FINE STRUCTURE IN THE $\tilde{a}^{3}B_{1}$ STATE OF $SO_{2}$

Author Institution: Department of Chemistry, University of British ColumbiaRotational analyses have been carried out for the (0,0) band of the ${\tilde{a}}^{3}B_{1}$-minus ${\tilde{X}^{1}}A_{1}$, absorption systems of $S^{16}O_{2}$ and $S^{18}O_{2}$ , from high dispersion plates taken with the gases at dry ice temperature. The rotational analysis of the (0,0) band of $S^{16}O_{2}$ given by Brand, Jones, and di Lauro is confirmed in general, but their values for the anisotropic electron spin fine structure constants are found to be seriously in error. Our new values remove the discrepancy in the sign of the spin-spin interaction parameter $\beta = E$ between the gas phase work and the solid state value given by Tinti. This discrepancy had been rationalized by Brand et al., in terms of a different choice of phases for the angular momentum operators, but this argument is shown to be incorrect. The spectrum of $S^{18}O_{2}$ confirms our new values completely except for the parameter ${\epsilon}_{bb}$ , where perturbation by the nearby ${\tilde{b}}^{3}A_{2}$ state is presumably responsible