title: Quantum-Classical Calculation of Vibronic Spectra along a Reaction Path: The Case of the ECD of Easily Interconvertible Conformers with Opposite Chiral Responses.
abstract: We present a novel mixed method suitable for computing the low-to-middle resolution spectra of systems characterized by a large-amplitude motion s (defined by either a reaction or an internal path) coupled to a bath of harmonic oscillators r, which change with s. The method is based on an adiabatic approximation whereby s is considered much slower than r degrees of freedom and is treated classically. We show that the spectrum can be obtained by a suitable average of quantum vibronic spectra of the fast coordinates computed at representative values of the slow coordinate along the path. By our method we calculate the electronic circular dichroism (ECD) of 2,2,2-trifluoro-anthryl-ethanol, which possesses two conformers with opposite chirality separated by a low-energy barrier. Path-averaged spectra are significantly different from those obtained only at the stable minima: Agreement with experiment is improved. The method represents a generalization of those currently based on harmonic approximation.
authors.affiliation: CNR-Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organo Metallici (ICCOM-CNR), SS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy.
authors.forename: Javier
authors.initials: J
authors.lastname: Cerezo
authors.affiliation: Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia , Viale Europa 11, I-25123 Brescia, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Mazzeo
authors.affiliation: Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia , Viale Europa 11, I-25123 Brescia, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Longhi
authors.affiliation: Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia , Viale Europa 11, I-25123 Brescia, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Abbate
authors.affiliation: CNR-Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organo Metallici (ICCOM-CNR), SS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Santoro