Anomalous simplicity of the (A)over-tilde -> (X)over-tilde dispersed fluorescence spectrum of (C2H2)-C-13

Dispersed fluorescence (DF) spectra, from several bands in the ii state of (C2H2)-C-13 were recorded with 18 cm-l resolution. The spectra are analyzed using standard pattern recognition techniques in order to extract the brig ht state fractionation patterns. A comparison is made between the DF spectr a of (C2H2)-C-13 and (C2H2)-C-12 At low energy, the DF spectrum of (C2H2)-C -13 appears similar to that of (C2H2)-C-12, other than the expected isotopi c shifts. Surprisingly, the DF spectra of (C2H2)-C-13 at high energy are si mpler than the corresponding spectra of (C2H2)-C-12, reflecting simpler str etch-bend dynamics. This simplicity can be qualitatively explained due to a detuning of the 3245 resonance. (C) 2001 Elsevier Science B.V. All rights reserved.