THE LABORATORY ROTATIONAL SPECTRUM OF $ISO$-PROPYL CYANIDE AND AN ASTRONOMICAL SEARCH IN SAGITTARIUS B2(N)

A.~Belloche, K.~M.~Menten, C.~Comito, H.~S.~P. Muller, P.~Schilke, J.~Ott, S.~Thorwirth, C.~Hieret, {\it Astron. Astrophys.H.~S.~P. Muller, A.~Belloche, K.~M.~Menten, C.~Comito, P.~Schilke, {\it J. Mol. Spectrosc.A.~Belloche, R.~T.~Garrod, H.~S.~P. Muller, K.~M.~Menten, C.~Comito, P.~Schilke, {\it Astron. Astrophys.G.~E.~Herberich, {\it Z. Naturforsch.J.~R.~Durig, Y.~S.~Li, {\it J. Mol. Struct.Author Institution: I. Physikalisches Institut, Universitat zu Koln, 50937 Koln; and Max-Planck-Institut fur Radioastronomie, 53121 Bonn, Germany; CESR, Universite de Toulouse (UPS), and CNRS, 31028 Toulouse, France; Institut fur Physikalische Chemie und Elektrochemie; Lehrgebiet A, Universitat Hannover, 30167 Hannover, Germany; Max-Planck-Institut fur Radioastronomie, 53121 Bonn, Germany; I. Physikalisches Institut, Universitat zu Koln; 50937 Koln, GermanyWe have carried out a molecular line survey of Sagittarius B2(N) in the 3\,mm region with selected recordings at 2 and 1.3\,mm to probe the chemical complexity in massive star-forming regions. Noteworthy results include the detection of aminoacetonitrile, {\bf 482} (2008) 179; Erratum {\bf 492} (2008) 796.} a possible precursor of the aminoacid glycine, the detection of $^{13}$C isotopologs of vinyl cyanide, {\bf 251} (2008) 319.} and the detection of ethyl formate as well as $normal$-propyl cyanide. (2009), accepted.} The heavy atoms in the latter molecule form a chain. An isomer with a branched structure, $iso$-propyl cyanide, also exists, but its rotational spectrum has only been recorded in few transitions up to 40\,GHz. {\bf 22a} (1967) 543.} {\bf 21} (1974) 289.} Therefore, laboratory measurements were extended. The molecule is rather asymmetric ($\kappa = -0.5766$) with a strong $a$-dipole moment component of 4.05~(2)~D and a still sizable $c$-component of 1.4~(2)~D.$^e$ Measurements in Koln were carried out in selected regions between 40 and 600\,GHz. Since the $c$-type transitions appeared to be weaker than predicted additional Stark (and also zero-field) measurements have been carried out in Hannover between 6 and 20\,GHz. We will present results of these laboratory spectroscopic investigations as well as the outcome of a search for the molecule in our Sgr B2(N) line survey