Section of the rotational spectrum of CH₃¹⁷OH displaying the $J_{K_a,K_c}=1_{0,1}\leftarrow 0_{0,0}$ a-type transitions. The v_t = 0 transition of A symmetry appears at lower frequencies, while the v_t = 0 transition of E symmetry appears at higher frequencies. Both transitions are split into three HFS components whose upper and lower state F quantum numbers are indicated, which are often designated as F′ and F″, respectively.