Stepwise Nucleation of Aniline: Emergence of Spectroscopic Fingerprints of the Liquid Phase.

This work deals with the controlled nucleation of aniline from the isolated molecule until formation of a moderately large aggregate: aniline nonamer. The structure of the cluster at each step of the nucleation was unravelled combining mass-resolved IR spectroscopy and computational chemistry, demonstrating that aggregation is primarily guided by formation of extensive N-H⋅⋅⋅N hydrogen-bond networks that give the aggregates a sort of branched backbone, in clear competition with multiple N-H/C-H⋅⋅⋅π and π⋅⋅⋅π interactions. The result is the co-existence of close nucleation paths connecting relational aggregates. The delicate balance of molecular forces makes the aniline clusters a challenge for molecular orbital calculations and an ideal system to refine the present nucleation models. Noticeably, spectroscopic signatures characteristic of the condensed phase are apparent in the nanometer-size aggregates formed in this work.