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Positron lifetime spectra have been measured in a wide variety of molecular gases at pressures up to about thirty atmospheres. The spectra were analyzed to yield the free-positron annihilation rate (X« + ) and tripletpositronium quenching rate (\ q ) at unit pressure. Attachment of the free positrons occurs in many of the gases. For the others, a strong correlation between X« + and a, the electric-dipole polarizability at optical frequencies, is found, leading to a general relationship (for both molecular and atomic gases) between these two quantities. This is apparently the first experimental evidence that long-range dipole distortion is the predominant mechanism in low-energy positron scattering.

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