title: Noncovalent Interactions and Internal Dynamics in Pyridine-Ammonia: A Combined Quantum-Chemical and Microwave Spectroscopy Study.
abstract: The 1:1 complex of ammonia with pyridine is characterized by using state-of-the-art quantum-chemical computations combined with pulsed-jet Fourier-transform microwave spectroscopy. The computed potential energy landscape indicates the formation of a stable σ-type complex, which is confirmed experimentally: analysis of the rotational spectrum shows the presence of only one 1:1 pyridine-ammonia adduct. Each rotational transition is split into several components owing to the internal rotation of NH3around its C3axis and to the hyperfine structure of both14N quadrupolar nuclei, thus providing unequivocal proof that the two molecules form a σ-type complex involving both a N-H⋅⋅⋅N and a C-H⋅⋅⋅N hydrogen bond. The dissociation energy (BSSE- and ZPE-corrected) is estimated to be 11.5 kJ mol-1. This work represents the first application of an accurate yet efficient computational scheme, designed for the investigation of small biomolecules, to a molecular cluster.
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Spada
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Tasinato
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy.
authors.forename: Fanny
authors.initials: F
authors.lastname: Vazart
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barone
authors.affiliation: Dipartimento di Chimica, "Giacomo Ciamician" dell'Università, Via Selmi 2, 40126, Bologna, Italy.
authors.forename: Walther
authors.initials: W
authors.lastname: Caminati
authors.affiliation: Dipartimento di Chimica, "Giacomo Ciamician" dell'Università, Via Selmi 2, 40126, Bologna, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Puzzarini
keywords: equilibrium structures; hydrogen bonds; pyridine-ammonia complexes; quantum chemistry; rotational spectroscopy