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Title: Matrix-Isolation FTIR Spectroscopy of Benzil:  Probing the Flexibility of the C−C Torsional Coordinate
Authors: Lopes, S. 
Gómez-Zavaglia, A. 
Lapinski, L. 
Chattopadhyay, N. 
Fausto, R. 
Issue Date: Sep-2004
Publisher: American Chemical Society
Serial title, monograph or event: J. Phys. Chem. A
Volume: 108
Abstract: The infrared spectrum and conformational flexibility of benzil, (C6H5CO)2, are studied by matrix-isolation FTIR spectroscopy, supported by DFT calculations. It is shown that the low-frequency (ca. 25 cm-1), large-amplitude torsion around the C−C central bond strongly affects the structural and spectroscopic properties exhibited by the compound. The equilibrium conformational distribution of molecules with different OC−CO dihedral angles, existing at room temperature in the gas phase, and trapped in a low-temperature (T = 9 K) inert matrix can be changed either by in situ irradiation with UV light (λ > 235 nm) or by annealing the matrix to higher temperatures (T ≈ 34 K). In the first case, the increase of the average OC−CO angle results from conformational relaxation in the excited electronic states (S1 and T1), whose lowest-energy conformations correspond, for both S1 and T1 states, to a nearly planar configuration with the OC−CO dihedral angle equal to 180°. In the second case, the decrease of the average value of the OC−CO dihedral angle is a consequence of the change in the So C−C torsional potential, resulting from interactions with the matrix media, which favors the stability of the more polar structures with smaller OC−CO dihedral angles.
DOI: 10.1021/jp047116s
Rights: openAccess
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais

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