Knowledge Bank

The rotational spectrum of methanol is characterized by an asymmetric top overall rotation coupled with an intermediate barrier three fold hindered rotation. The spectrum progresses from a torsionally modified asymmetric top in the $vt=0$ state to a rotationally modified torsion by the $vt=2$ state. The $vt=3$ state lies well above the torsional barrier and in close proximity to the CO stretch vibration. The $vt=3$ microwave spectrum has been assigned up to $J=34$ in over 1 THz of frequency measured spectra. In spite of the success in assigning the a-type R-branches the b-type spectra is surprisingly weak suggesting that the torsion significantly modifies the intensities of the few $K$ levels in close enough proximity to have transitions below 2.5 THz.