Knowledge Bank

The methanol spectrum from $550cm-1$ to $900cm-1$ (reported in the preceeding paper by D. R. Woods and C. W. Peters) arises principally from b-type transitions between the torsion-rotation levels of the molecule. In these transitions $\Delta K=\pm 1;\Delta J=0$ (Q branch lines) and $\Delta J=\pm 1$ (P and R branch lines). In this region of the spectrum the upper state levels have high torsional quantum numbers, mainly, $n=3$ and 4, whereas the lower states have $n=0$ and 1. The significant values of K range from 0 to around 12 and hence the effects of perturbing terms become quite large. Using the molecular constants derived by Lees and $Baker1$ from the microwave spectrum, a preliminary spectrum was calculated which included all P, Q and R branch lines above a preassigned intensity. The agreement with the experimental spectrum was sufficiently good to allow an identification of a great many of the lines and consequently a more accurate determination of the energy levels. By making use of these, together with the line widths and the spectrometer resolution, the spectrum has been recomputed and compared with the observations.