Knowledge Bank

The symmetric stretching of the methyl group ($v1$) of $CH3NC$ has been recorded using a Fourier Transform Spectrometer with an unapodized resolution of $0.004cm-1$. The rotational structure has been revealed for the first time, and the molecular constants have been obtained. Over 400 spectral lines have been assigned to the P- and R-transitions of this parallel band with $K=0$ to $K=6$ and $J=40$. The rotational structure of the $v1$ is quite different from a typical parallel band (e.g., $v4$ of $CH3NC$ because of the small $\Delta$(B) and large $\Delta$(A-B) values, giving rise to an intermingling of spectral lines belonging to different J-multiplets. In addition, all of the K-subbands have been observed to he strongly perturbed. The structure analysis, spectral assignment, and perturbation origin will be discussed in this presentation.""