An MS Xα and ETS study of the influence of “d” orbitals on the electron affinities of thio-substituted benzenes

The electron transmission spectra of the o,o′-dimethyl substituted benzenes 2,6-(CH₃)₂C₆H₃-XR (X = O,S, NR: R = H, CH₃) show that the substituents adopt a planar (R = H) or rotated (R = CH₃) conformation depending upon their size and they suggest that in the sulphur derivatives the ²B₁ H anion states are stabilized by S3d orbital participation. MS Xα calculations performed on both the planar and orthogonal forms of the model systems p-(XH)₂-C₆H₄ (X = O, S) support this hypothesis and assign the extra resonance present in the ET spectra of the thio derivatives to electron capture into σ_S-R* MOS. strongly mixed with sulphur 3d orbitals ( = 33% d character).