Rotational spectroscopy, dipole moment and ${}^{14}$N nuclear hyperfine structure of $iso$-propyl cyanide

Rotational transitions of $iso$-propyl cyanide, (CH${}_3$)${}_2$CHCN, also known as $iso$-butyronitrile, were recorded using long-path absorption spectroscopy in selected regions between 37 and 600 GHz. Further measurements were carried out between 6 and 20 GHz employing Fourier transform microwave (FTMW) spectroscopy on a pulsed molecular supersonic jet. The observed transitions reach $J$ and $K_a$ quantum numbers of 103 and 59, respectively, and yield accurate rotational constants as well as distortion parameters up to eighth order. The ${}^{14}$N nuclear hyperfine splitting was resolved in particular by FTMW spectroscopy yielding spin-rotation parameters as well as very accurate quadrupole coupling terms. In addition, Stark effect measurements were carried out in the microwave region to obtain a largely revised $c$-dipole moment component and to improve the $a$-component. The hyperfine coupling and dipole moment values are compared with values for related molecules both from experiment and from quantum chemical calculations.