MoleculargValue, Magnetic Properties, and the Groundhyphen;State Electronic Structure of Fluoroacetylene

摘要

The firsthyphen;order molecular Zeeman effect observed in theJ=0rarr;J=1 rotational transition of FCtrpbnd;CH gives the magnitude of the moleculargvalue perpendicular to the molecular axis to be 0.0071plusmn;0.0004. When combined with an estimate of the molar susceptibility, the moleculargvalue leads to an average value ofr2for electrons from the center of mass. The result is lang;psgr;0verbar;Sgr;iri2verbar;psgr;0rang;=37.9times;10minus;16cm2. An upper limit on the magnitudes of the proton and fluorine spinmdash;rotation interaction constants of 6ndash;8 kHz was established by highhyphen;resolution, microwave linewidth studies of theJ=0rarr;J=1 transition.The ground electronic state of fluoroacetylene is described by a set of 11 hybrid molecular orbitals, employing various hybridization and ionic parameters. The average values of nine onehyphen;electron operators were calculated using the 16 atomichyphen;orbital functions included in the minimal basis LCAO MO set. The Coulsonmdash;Barnett expansion technique was used in the calculation of the twohyphen; and threehyphen;center integrals. The calculations of the onehyphen;electron operators were made for considerable ranges in the adjustable parameters of the wavefunction.A besthyphen;fit wavefunction was obtained by fitting six of the onehyphen;electron operators to the experimentally determined properties. It was then used to compute the average value ofr2and the H and F diamagnetic shielding. The latter are combined with available chemicalhyphen;shift data to yield the H and F paramagnetic shielding and spinmdash;rotation constants. The results for the spinmdash;rotation constants are consistent with the upper limit established by the linewidths. Also, the theoretical value ofr2agrees very well with that determined experimentally. Several features of the electronic structure and groundhyphen;state wavefunction are discussed. For instance, we found negligiblescharacter in the fluorine atomic orbitals participating in the Fsngbnd;C sigma bound but a significant fluorine contribution to the Fsngbnd;C pi bond.