Author Institution: Department of Chemistry, Penn State University; Department of Physics, Penn state UniversityThe symmetric stretching of the methyl group (v1β) of CH3βNC has been recorded using a Fourier Transform Spectrometer with an unapodized resolution of 0.004cmβ1. 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 v1β is quite different from a typical parallel band (e.g., v4β of CH3βNC because of the small Ξ(B) and large Ξ(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."