Structural characterization of 1 : 1 van der Waals complexes of 9-cyanoanthracene with aprotic solvents by rotational coherence spectroscopy

Structures of 9-cyanoanthracene (CNA) clusters microsolvated with a single molecule of aprotic solvents (carbon dioxide, two isotopomers of acetonitri le, and fluoroform) have been studied by rotational coherence spectroscopy (RCS) implemented with the time-resolved fluorescence depletion method. All of the observed RCS traces exhibit pronounced C-type transients, and this fact suggests that these species are quite close to planar asymmetric tops with their electronic transition moments pointing to in-plane directions. W eak J-type transients have been also identified for CNA-CO2 and -CF3H, the latter of which shows A-type transients as well. By comparing the experimen tal observations with density functional theory calculations at the B3LYP/6 -31G(d,p) level, it is concluded that the solvent molecule is located by th e side of the CN group of CNA with its molecular axis lying in the CNA mole cular plane. All of the cluster geometries are of C, symmetry, in which a p ositively charged atom of the solvents (C, H, or H for CO2, CH3CN, and CF3H , respectively) is close to the cyano nitrogen of CNA, while an electonegat ive part (O, N, or F) contacts with the 1-position hydrogen of CNA. Some ge ometrical parameters including the centers of mass separation are obtained from the RCS-derived rotational constants.