Knowledge Bank

The rotational spectrum of $n$-butyl cyanide (C$4$H$9$CN) was measured between 75 and 130~GHz using a novel all-solid-state spectrometer with a total absorption path of 44~m. In the course of the analysis of the spectrum, about 3000 transitions were assigned and a full set of quartic centrifugal distortion parameters with some sextic and octic terms could be determined for each of the three known conformers (anti-anti, anti-gauche(methyl end) and gauche(CN end)-anti). The work was motivated by the fact that $n$-butyl cyanide is likely to be found in interstellar hot core environments. This is indicated by the discovery of $n$-propyl cyanide (C$3$H$7$CN), the next smaller alkyl cyanide, in the ISM, 215 (2009)}. The increased accuracy of the model, which will be additionally extended by future laboratory measurements around 200~GHz, may now be employed for a prediction of the spectrum up to 300~GHz with a feasible uncertainty for astronomic line surveys. Furthermore, there are two less abundant conformers, \emph{cis}-gauche-gauche and \emph{trans}-gauche-gauche, which have not yet been detected in the rotational spectrum, 293 (1997)}. Due to the increased sensitivity of the new spectrometer, it seems possible now for the first time to identify their sectroscopic fingerprints in the recorded data.