title: Molecular Structures of Methyldifluoroarsine, CH(3)AsF(2), and Dimethylfluoroarsine, (CH(3))(2)AsF, in the Gas Phase As Determined by Electron Diffraction and ab InitioCalculations.
abstract: The structures of gaseous CH(3)AsF(2) and (CH(3))(2)AsF have been determined by electron diffraction incorporating vibrational amplitudes derived from ab initio force fields scaled by experimental frequencies and, for the difluoride, restrained by microwave constants. The following parameters (r(alpha) degrees structure, distances in pm, angles in degrees) have been determined for CH(3)AsF(2): r(As-C) = 194.6(4), r(As-F) = 173.1(1), angleCAsF = 95.2(1), angleFAsF = 97.0(1). For (CH(3))(2)AsF structural refinement gives r(As-C) = 195.1(1), r(As-F) = 175.4(1), angleCAsF = 95.3(5), and angleCAsC = 96.9(8). For the series (CH(3))(3)As, (CH(3))(2)AsF, CH(3)AsF(2), and AsF(3), both As-C and As-F bond lengths are shortened with increasing numbers of F atoms, but the angles CAsF and FAsF are almost invariant.
authors.affiliation: Department of Biological and Molecular Sciences, University of Stirling, Stirling, FK9 4LA, U.K.
authors.forename: Anthony J.
authors.initials: AJ
authors.lastname: Downs
authors.forename: Tim M.
authors.initials: TM
authors.lastname: Greene
authors.forename: G. Sean
authors.initials: GS
authors.lastname: McGrady
authors.forename: Neil
authors.initials: N
authors.lastname: Townson
authors.forename: Paul T.
authors.initials: PT
authors.lastname: Brain
authors.forename: Colin R.
authors.initials: CR
authors.lastname: Pulham
authors.forename: David W. H.
authors.initials: DW
authors.lastname: Rankin
authors.forename: Heather E.
authors.initials: HE
authors.lastname: Robertson
authors.forename: Bruce A.
authors.initials: BA
authors.lastname: Smart
authors.forename: Ian L.
authors.initials: IL
authors.lastname: Alberts