Molecular calculations of moments of the induced spectra for N2, O2, and CO2

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Abstract
Two moments of the induced absorption spectra for gaseous N2, O2, and CO2 are calculated and compared with experiment. The theoretical expressions evaluated are those for spectra due to quadrupole‐induced dipoles in molecules with anisotropic polarizability. The intermolecular interaction functions used include the effects of nonspherical shape by modelling the potential as a sum of quadrupolar plus atom–atom energies with parameters that are known to give realistic values for a number of other measured properties. Satisfactory agreement between the calculation and experiment was obtained in the binary interaction limit if hexadecapolar contributions are assumed to be present in the case of O2. These intermolecular potentials are then used together with an approximate theory for the requisite correlation functions in an evaluation of the spectral moments for liquid N2 and O2. It was found that the agreement between experiment and theory for the liquid improved dramatically when three‐body contributions to the spectral moments were included in the calculation.