Abstract
The dipole (α), quadrupole (C), and dipole–octopole (E) polarizabilities, the dipole–dipole–quadrupole (B) and second dipole (γ) hyperpolarizabilities, and the quadrupole (θ) and hexadecapole (Φ) moments are calculated for the ground state of CO2 at its equilibrium geometry. The values are obtained from fourth-order many-body perturbation theory energies of CO2 in the presence of various configurations of point charges. Electron correlation affects the longitudinal components more than the transverse ones; hence, electron correlation effects are greater for the anisotropies than for the isotropic averages of these properties. Our best vibrationless estimates for the isotropic values are ᾱ≂17.63 e2a20E−1h, C̄≂77.8 e2a40E−1h, B̄≂−2.1×102 e3a40E−2h, γ̄≂1.20×103 e4a40E−3h, and θzz≂−3.24 ea20. The quadrupole moment, mean dipole polarizability and hyperpolarizability are in satisfactory agreement with experiment. On the other hand, the polarizability anisotropy Δα≂14.3 e2a20E−1h agrees with experimental estimates based on Rayleigh scattering depolarization ratios but not with those based on the Kerr and Stark effects. Further theoretical and experimental work on the vibrational contributions to Δα is needed to resolve this discrepancy. The hexadecapole moment is small in magnitude, and is very sensitive to both basis set and electron correlation effects; its accurate prediction will be a challenge for quantum chemical methods.
Published Version
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