Abstract
We have calculated self-consistent field (SCF) and second-order Møller-Plesset perturbation theory (MP2) for the dihaloethynes X–C≡C–X, X = F, Cl, Br and I. All calculations have been performed with carefully optimized, flexible basis sets of gaussiantype functions. Our best values for the quadrupole moment (Θ/ea02) are -0.6524 (FCCF), 3.6612 (ClCCCl), 5.8143 (BrCCBr) and 8.3774 (ICCI). The dipole polarizability is strongly anisotropic. For the mean (α /e2a02Eh-1) and the anisotropy (Δα/e2a02Eh-1) we obtain 23.58 and 15.09 (FCCF), 51.75 and 48.30 (ClCCCl), 66.53 and 60.04 (BrCCBr), 93.79 and 78.91 (ICCI). The mean dipole hyperpolarizability (γ /e4a04Eh-3) increases rapidly as 2932 (FCCF), 9924 (ClCCCl), 17409 (BrCCBr) and 35193 (ICCI). The transversal component of the hyperpolarizability is larger than the longitudinal one for FCCF, γxxxx > γzzzz but this is reversed for the other molecules in the series. Difluoroethyne is less (hyper)polarizable than ethyne.
Highlights
Introduction2. Theory The energy of uncharged molecule in a weak, static electric field can be written as [37,38]
The dihaloethynes X–C≡C–X (X = F, Cl, Br and I) represent a multiply interesting class of molecules
The calculated values for the four dihaloethynes are given in Tables 1(FCCF), 2(ClCCCl), 3(BrCCBr) and 4(ICCI)
Summary
2. Theory The energy of uncharged molecule in a weak, static electric field can be written as [37,38]. The number of independent components needed to describe the electric multipole moment or polarizability tensors depends on the molecular symmetry [37]. For linear non-polar molecules, as the dihalogenated ethynes, μα0 = Ωαβγ0 = 0, while there is only one independent component for either the quadrupole or the hexadecapole moment [37]. For the (hyper)polarizability there are two independent components for ααβ and three for γαβγδ [37]. In addition to the Cartesian components we calculate mean values and anisotropies for the (hyper)polarizability defined as [37]. We extract the dipole (hyper)polarizability values from the energy of the molecule perturbed by weak, static homogeneous fields [32]. The MP2 values of Θ and Φ are obtained through the MP2 density [42]
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