Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide

Arnaud Belloche, Robin T. Garrod, Holger S. P. Müller, Karl M. Menten

Science 26 September 2014:
Vol. 345 no. 6204 pp. 1584-1587
DOI: 10.1126/science.1256678



The largest noncyclic molecules detected in the interstellar medium (ISM) are organic with a straight-chain carbon backbone. We report an interstellar detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an abundance 0.4 times that of its straight-chain structural isomer. This detection suggests that branched carbon-chain molecules may be generally abundant in the ISM. Our astrochemical model indicates that both isomers are produced within or upon dust grain ice mantles through the addition of molecular radicals, albeit via differing reaction pathways. The production of iso-propyl cyanide appears to require the addition of a functional group to a nonterminal carbon in the chain. Its detection therefore bodes well for the presence in the ISM of amino acids, for which such side-chain structure is a key characteristic.