Low Energy Isomers and Infrared Spectra Simulations of C4H3N, C4H4N, and C4H5N 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 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.