Torsional spectrum of 12CH313CH3: A 2-state frequency analysis of the torsional bands and the ν12 vibrational fundamental

The far-infrared spectrum of 12CH313CH3 is studied between 220 and 350cm-1 at an effective resolution of 0.004-0.005cm-1 using a Bruker IFS-120 HR. Observation of the torsional fundamental ν6(289cm-1) and the torsional hot band 2ν6-ν6(255cm-1), together with the lowest frequency vibrational fundamental ν12(821.5cm-1), also obtained with the same spectrometer at an effective resolution of 0.0025cm-1, gives information on the torsional stack of the ground vibrational state and that for v12=1 state. The frequencies are analyzed in terms of a 2-state fit to determine the torsion mediated Coriolis interactions between the torsional stacks. A comparison is made with a 2-state fit of similar data for 12CH312CH3.