EXPERIMENTAL CIRCULAR-DICHROISM AND VUV SPECTRA OF SUBSTITUTED OXIRANES AND THIIRANES

Highly resolved circular dichroism spectroscopy of alkyl-substituted o xirane and thiirane chromophores was investigated in the vacuum ultrav iolet region up to 9.0 eV (138 nm) using synchrotron radiation. Compar ison of the gas phase and liquid phase spectra, along with results fro m theoretical calculations, could confirm the predicted Rydberg charac ter of some excited states including their fine structures. The n(O) - -> R(3d) Rydberg transitions in chiral methyloxirane and the predicted n(S) --> sigma valence transition of (S, S)-(-)-(2,3)-dimethylthiira ne were detected for the first time. It could be shown that the quadra nt rule for the first state previously verified for some chiral oxiran es also holds for (R)-(-)-1,2-epoxy-3-methyl-butane and (R)-(-)-1,2-ep oxy-4-methyl-pentane and is found to be expandable for thiiranes. The first ns Rydberg transitions of dimethyloxirane could be fitted to a t erm formula.