The research carried out in the Laboratory Astrochemistry Group deals mostly with a very
special kind of chemistry - that of the interstellar medium. Some 170 chemical compounds
were hitherto identified in the interstellar space. Among those, the profusion of chain
molecules, held together by carbon backbones with multiple bonds, is striking.
Cyanopolyacetylenes, H-(CC)n-CN (with n=1-5), methylcyanoacetylene H3C-C≡C-C≡N or
allenyl cyanide H2C=C=CH-C≡N constitute representative examples. The astrochemical
importance of such molecules is not confined to inter- or circumstellar environments; it may
extend to Solar System bodies such as Titan, (the gigantic Saturn’s moon), Triton, (satellite of
Neptune) or comets.
The interpretation of astronomical spectral data cannot be accomplished without any prior
knowledge coming from laboratory measurements. Paradoxically, the molecules of interest most abundant in the Galaxy, and possibly also in the entire Universe - are often unstable
and/or hard to synthesize with standard chemical methods. Our current research concentrates
on 1) detailed spectroscopic studies of molecules already discovered in space; 2) predicting
the properties of “new”, i.e. thus far unknown, yet potentially interstellar species (when
possible, we try to synthesize them); 3) looking for possible interstellar synthesis pathways;
4) analysing the astronomical spectra.
Cyanoacetylene (H-C≡C-C≡N) found in the dense clouds of interstellar gas, and in some
evolved circumstellar shells, is the archetype for a family of cyanopolyacetylenes, and for a
multitude of related isomers, radicals, and ions. The interstellar microwave (pure rotational)
emissions from two isomers of this compound, namely an isonitrile HCCNC, and imine
HNCCC - were found in early 1990s. Noteworthy, the radio astronomical detection methods,
based on the rotations of gas-phase molecules, are as a rule not useful for highly symmetric
species. An alternative technique, that of infrared (IR) spectroscopy, is free (for polyatomic
species) from this limitation, and has indeed proved its value, e.g. with the discoveries of
interstellar acetylene, diacetylene, triacetylene or benzene.
Figure 1. UV irradiation of a cryogenic solid doped with cyanoacetylene, HC3N, leads to an ‘in situ’
creation of longer chains – HC5N, C4N2, and C6N2 – detected via their strong electronic luminescence.
[Phys. Chem. Chem. Phys. 13 (2011) 16780]
The IR spectra of HCCNC and HNCCC were observed in our group following the far-UV
photolysis of cyanoacetylene dispersed in solid argon at about 10 K. In addition, two other
interesting species appeared, namely the new isomer HCNCC, and the C3N‒ anion (in
coincidence with the discovery of first anions, including C3N‒ , in space). Likewise, we have
uncovered at least 3 isomers, and the C5N‒ anion, as the products of HC5N photolysis. A
remarkable discovery in this line of our laboratory research consists in the detection of
intermolecular coupling processes, leading to the photochemical growth of carbon chains,
among which we have detected (via their strong electronic luminescence) dicyanoacetylene,
cyanodiacetylene, and dicyanodiacetylene molecules created out of HC3N (Figure 1).
Rare gas solids (neon, argon, krypton or xenon) proved useful for the photochemical
synthesis and isolation of unstable chemical species. In the majority of cases we do not
employ this environment with the intention of simulating the astrochemical environments, but
rather as a playground for investigating the spectroscopy (unknown, to a large extent) and
chemistry of otherwise unstable photochemical products. Not only are the solidified rare
gases chemically inert, but they are also transparent to the radiation throughout a vast spectral
range, from far-IR to vacuum-UV. The majority of our experiments are based on the
ultraviolet photolysis of appropriate precursor compounds trapped in rare gas crystals.
Alternatively, the gaseous mixture of rare gas atoms with precursor molecules can be
subjected to electrical discharges (prior to solidification) which widens the variety of obtained
products (Figure 2). Another possibility consists in using non-inert cryogenic environments
(e.g. solid para-hydrogen, water, carbon oxide, methane), with the goal of mimicking, to
same extent, the photochemistry taking place in interstellar ices.
Another approach to astrochemistry is accomplished with quantum chemical calculations,
namely by searching for simple, yet thus far unknown arrangements of basic elements, which
could reasonably be proposed as candidates for interstellar molecules. These investigations
resulted e.g. in the discovery of CCCNCN molecule (which was first theoretically predicted,
and subsequently found in the laboratory) or in a theoretical study on the feasibility of
interstellar cyanovinylidene CC(H)CN synthesis. One of the current topics deals with
the origin of astrochemical molecules HNCS and NCSH.
Figure 2. Solid krypton (temp. of 8 Kelvin) doped with cyanoacetylene (HC 3N), subjected to electric
discharges. Luminescence is mostly due to C6N2 and C3N– molecules that arise following the
dissociation of HC3N. [Ann. Centre Sci. APS, 9 (2010) 35]
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