Construction of interstellar cumulenes and heterocumulenes: Mass spectrometric studies

The last few years have brought an increasing interest in the chemistry of rite interstellar and circumstellar environs. Many of the molecular species discovered in remote galactic regions have been dubbed 'non-terrestrial' b ecause of their unique structures (Thaddeus et al, 1993). These findings ha ve provided a challenge to chemists in many differing fields to attempt to generate these unusual species in the laboratory of particular recent inter est have been the unsaturated hydrocarbon families, CnH and CnH2, which hav e been pursued by a number of diverse methodologies. A wine range of hetero cumulenes, including CnO, HCnO, CnN, HCnN, CnS, HCnS, CnSi and HC,Si hale a lso provided intriguing targets for laboratory experiments. Strictly the te rm cumulene refers to a class of compounds that possess a series of adjacen t double bonds, with allene representing the simplest example (H2C=C=CH2). However for many of the non-terrestrial molecules presented here, the carbo n chain cannot be described in terms of a single simple valence structure, ann so we use the terms cumulene and heterocumulene in a more general sense : to describe molecular species that contain an unsaturated polycarbon chai n. Mass spectrometry has proved ail invaluable tool ill the quest for inter stellar cumulenes and heterocumulenes in the laboratory it has the ability in its many forms, to (i) generate charged analogs of these species (ii) th e gas phase, (ii) probe their connectivity, ion chemistry: and thermochemis try and (iii) in some cases, elucidate the neutrals themselves. Here, we wi ll discuss the progress of these studies to this time. (C) 1999 John Wiley & Sons, Inc.