Low Energy Isomers and Infrared Spectra Simulations of C 4 H 3 N, C 4 H 4 N, and C 4 H 5 N and Related Ions.

The relative stability of pyrrole derivatives were investigated by applying a global minimum (GM) search for the low-lying energy structures of C 4 H 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 C 4 H 5 N and C 4 H 4 N compounds. In particular, the structures of the cationic and neutral C 4 H 3 N 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 C 4 H 4 N + and C 4 H 4 N 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.