Electric quadrupole and hexadecapole moments for X2C=CX2, X = H, F, Cl, Br, and I

We have calculated electric quadrupole and hexadecapole moments for ethene, tetrafluoroethene, tetrachloroethene, tetrabromoethene, and tetraiodoethene. A large basis set of [9s6p5d2f/5s4p2d] size is thought to provide reference near-Hartree-Fock results for the electric multipole moments of ethene: Theta(xx) = 1.34 and Theta(zz) = 1.53 ea(0)(2) for the quadrupole Phi(xxxx) = -17.38, Phi(yyyy) = 20.29, and Phi(zzzz) = -17.04 ea(0)(4) for the hexadecapole moment (with z as the C=C axis and the molecule on the xz plane). The electron correlation correction to the above values is estimated from coupled cluster calculations as Theta(xx) = -0.12 and Theta(zz) = -0.34 ea(0)(2) for the quadrupole and Phi(xxxx) = 1.26, phi(yyy) = -1.30, and Phi(zzzz) = 1.80 ea(0)(4) for the hexadecapole moment. For the halogenated ethenes we have obtained the following quadrupole moment values from second-order Moller-Plesset perturbation theory calculations: Theta(xx) = -1.14 (C2F4), 1.94 (C2C4), 3.61 (C2Br4), 6.84 (C2I4) and Theta(zz) = -1.04 (C2F4), -0.41 (C2Cl4), -0.15 (C2Br4), -0.87 (C2I4) ea(0)(2) (C) 2002 Wiley Periodicals, Inc.