Knowledge Bank

The CO stretch and hydroxyl bend bands of normal and of deuterated methanol have been observed under high dispersion (resolution $\cong$ $0.07cm-1$). These bands are predominantly of the a-type, $\Delta$K=0, and should closely resemble the parallel bands of a symmetrical top molecule and thus have simple P, Q and R branches. The CO stretch bands of $CD3OH$ $CH3OD$ and $CD3OD$ conform quite well with this prediction. The CO stretch of $CH3OH$ and all the hydroxyl bend bands exhibit the flature that the P and R branch lines are multiple with a spread of components which is essentially independent of the J number. It seems most probable that this is due to a change in the barrier height in the excited vibrational state. The CO stretch band of $CH3OH$ has been computed under this assumption. A satisfactory agreement with the observed spectrum is obtained providing the barrier in the excited state is taken to be $19cm-1$ higher than that ($375cm-1$) in the normal state.