Carbon-nitrogen chains of astrophysical importance

Some 130 hitherto revealed interstellar molecules were identified mostly by means of the microwave astronomy. However, the microwave detection (rotational spectroscopy) can only be applied to chemical species bearing substantial electric dipole moments. Infrared spectroscopic searches, free from this limitation, were recently very successful in astrochemical studies [1]. The interpretation of observational IR data relies on the knowledge of vibrational frequencies of certain exotic molecules – often hard to obtain in laboratories. Our work is aimed primarily at the cryogenic (rare gas matrix) isolation, and subsequent measurement of IR spectra for unstable compounds with the established or probable interstellar relevance [2]. This yielded vibrational frequencies of unsaturated chain molecules like HNCCC [3,4] (already discovered in space), NC5NC [5] or CNC4NC [6]. An alternative way consists in carrying out the quantum chemical calculations for a variety of atomic arrangements, pinpointing promising, yet thus far unknown, “interstellar-like” molecules. This tactics directed us to linear chains of HCNCC [7] and CCCNCN [8], and to cyanovinylidenes – for which reasonably high stabilities were predicted. The laboratory detection of HCNCC and CCCNCN followed shortly thereafter [9]; it is presently a challenge to find these species in space.