Knowledge Bank

Assignments of far-infrared (FIR) laser lines of $CH3OH$ originating from excited states other than the normal pure CO-stretch mode will be discussed. First, laser lines optically pumped by the 9R(18), 10P(12) and 13-9R(18) $CO2$ laser lines will be examined. It is proposed that each of these FIR laser systems involves highly excited n=3 torsional levels of the ground vibrational state, in two cases interacting via Fermi resonance with $n=0,C-O$ stretch levels. Secondly, FIR emission from $CH3$ deformation and $CH3$ in-plane rocking modes, pumped by the 9P(40), 10R(44), 13-9P(14) and 13/18-9P(34) $CO2$ lines, will be considered. Probable assignments will be presented, along with supporting spectroscopic evidence from combination frequency loops formed from observed or calculated IR and FIR frequencies.