Two-photon excitation of the [formula omitted] state of sulfur dioxide

Abstract

The two-photon excitation (TPE) spectrum of sulfur dioxide is reported in the region of the C ̃ 1B 2 ← X ̃ 1A 1 [2b 1(π ∗) ← 1a 2(π)] transition. The spectrum shows considerable rovibronic structure; the band contours are identified as arising from Δ K −1 = ± 1 transitions and rotational features are assigned by comparison with synthetic spectra generated from known rotational constants. The vibronic structure observed in TPE is quite similar to that observed in the one-photon spectrum: no zero-rank tensor transitions to levels with odd v 3 are identified, though they are allowed in the presence of vibronic coupling. The vibronic intensity distribution in the TPE spectrum below the dissociation limit is similar to that in one-photon absorption. However, near the dissociation threshold (5.63–5.67 eV), marked intensity redistribution occurs, from which it is concluded that the lowest energy photo-dissociation process proceeds through asymmetric stretching of the SO bonds.