Methyl group internal rotation A–E line splittings in several torsionally excited states of methyl glycolate and 2-methoxyethanol

The rotational spectra of several torsional satellites of methyl glycolate and 2-methoxyethanol have been investigated.The methyl barrier to internal rotation in methyl glycolate increases with the torsional quantum number of the C-C skeletal torsion, for which A–E line splittings have been measured up to v_SK=3. The V₃ value determined from the A–E line splittings in the first excited state of the methyl internal rotation is nearly the same of that previously determined in the ground state.For 2-methoxyethanol the V₃ barrier as determined from the A–E line splittings in the ground state is about 20% lower than the value previously obtained from the splittings observed in the first excited state of the methyl internal rotation. The sequence of the A–E splittings in the first excited state of the O-C skeletal torsion (v_SK=1) is probably reversed with respect to the ground state, while in the v_SK=2 state the sequence is like that in the ground state.