The Resonance Fluorescence Spectrum of Sulfur Dioxide

The 2100 Å line of Zn+ excites strong resonance fluorescence in sulfur dioxide gas. Vibrational analysis shows that the fluorescence bands form progressions of about 5 members in ν1, ν2, and ν3, singly and in combination. Although the occurrence of transitions to odd- and even-numbered levels of ν3 without discernable alternation in intensity is unexplained, the widespread activity of ν3 provides strong physical evidence for an unsymmetrical (Cs) structure in the upper state of the transition. Rotational analysis indicates that the transition moment is parallel, or nearly parallel, to the a axis and therefore that the upper electronic state of these transitions has B2(A′) orbital symmetry.