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

Abstract

We 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.