The
relative stability of pyrrole derivatives were investigated
by applying a global minimum (GM) search for the low-lying energy
structures of C4H
n
N (n = 3–5) clusters at neutral, anionic, and cationic
states. Several low-energy structures, previously not reported, were
identified. The present results reveal a preference for cyclic and
conjugated systems for the C4H5N and C4H4N compounds. In particular, the structures of the cationic
and neutral C4H3N species are different from
the anionic ones. For the neutrals and cations, cumulenic carbon chains
were found, while for the anions, conjugated open chains were obtained.
Of particular relevance, the GM candidates C4H4N+ and C4H4N are different from
those reported previously. For the most stable structures, infrared
spectra were simulated and the main vibrational bands were assigned.
Also, a comparison with available laboratory data was done aiming
to corroborate with experimental detection.