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Multireference ab initio calculations (by using the extended multiconfiguration quasi-degenerate second-order perturbation theory method XMCQDPT2) have been employed to determine the static polarizabilities for the ground triplet ( ) and two excited singlet (a1Δg and ) electronic states of molecular oxygen. The corrections to polarizabilities for the nuclear zero point motion are also reported. It was revealed that the excitation of an O2 molecule into the lowest singlet electronic states leads to a decrease in its polarizability: the polarizabilities of O2(a1Δg) and O2( ) are smaller (by factors of 0.967 and 0.962, respectively) than that of O2( ). The theoretical results for the state were quantitatively confirmed experimentally employing the diffraction at laser-induced gratings.

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