# STRUCTURE OF THE FLUOROBENZENE-HCI VAN DER WAALS COMPLEX BY MICROWAVE SPECTROSCOPY AND AB INITIO CALCULATION

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 Title: STRUCTURE OF THE FLUOROBENZENE-HCI VAN DER WAALS COMPLEX BY MICROWAVE SPECTROSCOPY AND AB INITIO CALCULATION Creators: Peebles, Sean A.; Peebles, Rebecca A.; Kuczkowski, R. L.; Boman, Faith C.; Sanz, M. Eugenia; Antolinez, Sonia; Alonso, José L.; López, Juan C.; Kraka, Elfi; Cremer, Dieter Issue Date: 2003 Publisher: Ohio State University Abstract: The structure of the fluorobenzene-HCl complex has been studied by Fourier-transform microwave spectroscopy and ab initio calculations. Rotational constants for three isotopomers ($C_{6}H_{5}F-H^{35}Cl, C_{6}H_{5}F-H^{37}Cl$ and $C_{6}D_{5}F-H^{35}Cl$) are consistent with a $\pi$-hydrogen bonded structure with the HCl located above the fluorobenzene ring, near the ring center, and the H atom of HCl pointing towards the $\pi$-cloud of the ring. Two structures are consistent with the inertial data, one with the HCl almost perpendicular to the ring and the other with the H pointing toward the fluorine end of the ring. Ab initio calculations at the $MP2/6-311++G(2df,2pd)$ level (+ BSSE corrections) were carried out to obtain difference electron density plots and indicate that the HCl is tilted by about $14^{\circ}$; from perpendicular, with the H atom toward the para carbon atom (where the $\pi$-density is significantly higher). An internal semi-circular libration of the H atom is possible, leading to an average inclination angle of about $0.7^{\circ}$, in reasonable agreement with the first of the two possible experimental structures. The calculations indicate that the bonding in the fluorobenzene-HCl complex is primarily electrostatic in nature with about 5.5 melectron transferred from the benzene ring to the HCl. Calculation of the complex binding energy at the $CCSD(T)/6-311++G(2df,2pd) + CP(BSSE)$ level gives a value of 2.8 kcal/mole. Description: Author Institution: Department of Chemistry, Eastern Illinois University; Department of Chemistry, University of Michigan; Department of Chemistry, University of Michigan; Departamento de Quimica Fisica, Facultad de Ciencias, Universidad de Valladolid; Department of Theoretical Chemistry, G\""oteborg University URI: http://hdl.handle.net/1811/20823 Other Identifiers: 2003-MH-13