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. 
Holger S. P. M\"uller, Audrey Coutens, Adam Walters, Jens-Uwe Grabow,   Stephan Schlemmer
astro-ph.IM astro-ph.GA physics.chem-ph