Symmetry classification of the degenerate vibrational normal modes of ethane

Abstract

We determine the G 36(EM) (usually called G 36 † ) symmetry species of all the degenerate vibrational normal modes of ethane unambiguously. We are able to do this as a result of observing the K-dependence of the sign of the energy separation between the torsionally split levels of ν 4 + ν y combination states, where ν 4 is the torsion and ν y ⊂ E g of D 3 d , and by observing the lack of any intrinsic torsional splitting or broadening in the ν x fundamentals and hot ( ν 4 + ν x ) − ν 4 transitions ( ν x ⊂ E u of D 3 d ). It is found that in C 2H 6 all the E u normal modes of D 3 d correlate with E 1 d of G 36(EM) (and hence E′ of D 3 h ), and all the E g normal modes of D 3 d correlate with E 1 d of G 36(EM) (and hence E″ of D 3 h ). High-resolution Q branches of ν 8, ν 4 + ν 12, and ( ν 4 + ν 8) − ν 4 of C 2H 6 are shown as illustrations.