Torsional splitting of Q-branch transitions with K_a = 6−5 and K_c = J − K_a + 1 in the vibrational ground state of DME-¹³C₁. The solid lines connect predicted transitions belonging to the same torsional substate. Experimental data are shown as errorbars. The splitting displayed is the difference between the transition frequency observed or predicted and the frequency derived if all tunneling parameters are neglected.