Construction of interstellar cumulenes and heterocumulenes. Mass spectrometric and related studies

The last few years have brought an increasing interest in the chemistry of the interstellar and circumstellar environs. Many of the molecular species discovered in remote galactic regions have been dubbed 'non-terrestrial' because of their unique structures (Thaddeus et al., 1993). These findings have provided a challenge to chemists in many differing fields to attempt to generate these unusual species in the laboratory. Of particular recent interest have been the unsaturated hydrocarbon families, CnH and CnH2, which have been pursued by a number of diverse methodologies. A wide range of heterocumulenes, including CnO, HCnO, CnN, HCnN, CnS, HCnS, CnSi, and HCnSi have also provided intriguing targets for laboratory experiments. Strictly, the term cumulene refers to a class of compounds that possess a series of adjacent double bonds, with allene representing the simplest example (H2C=C=CH2). However, for many of the non-terrestrial molecules presented here, the carbon chain cannot be described in terms of a single simple valence structure, and so we use the terms cumulene and heterocumulene in a more general sense: to describe molecular species that contain an unsaturated polycarbon chain. Mass spectrometry has proved an invaluable tool in the quest for interstellar cumulenes and heterocumulenes in the laboratory. It has the ability, in its many forms, to (i) generate charged analogs of these species in the gas phase, (ii) probe their connectivity, ion chemistry, and thermochemistry, and (iii) in some cases, elucidate the neutrals themselves. Here, we will discuss the progress of these studies to this time. © 1999 John Wiley & Sons, Inc