Left: section of the rotational spectrum of EMS showing the 19_0, 19–18_1, 18 and 16_2, 15–15_2, 14 rotational transitions for trans and gauche conformers, respectively. For these transitions, the A − E splittings are irresolvable since they are smaller than the experimental broadening of the lines. The negative features marked with an asterisk are produced by the folding of the frequency-switched data and appear at ±25 MHz of each rotational transition. Middle: 36_3, 33–36_2, 34b-type Q-branch rotational transition for the trans conformer of EMS where the A − E splittings can be observed. Right: 33_5, 28–33_4, 29b-type Q-branch rotational transition for the gauche conformer of EMS with the A − E internal rotation components indicated.