Extended permutation-inversion groups for simultaneous treatment of the rovibronic states of trans-acetylene, cis-acetylene, and vinylidene

► Simultaneous group theory treatment of trans and cis acetylene and vinylidene. ► Extended permutation-inversion groups and character tables defined. ► ”Limited identities” defined for multiple-valued coordinate systems. ► Predicted rotational K-staggerings compared with experiment for S1-cis acetylene.