Binary approximation lineshape

Theory. If the invariants of the pair polarizability are known, along with a refined model of the intermolecular interaction potential, the lineshapes of binary spectra can be computed quite rigorously [227, 231, 271], Lineshape computations based on exact or approximate classical trajectories are known [196, 264, 276, 316, 337]. Such computations generate spectral functions that are symmetric, g — co) = g((o). For massive pairs at high enough temperatures, such classical profiles are often sufficient at frequency shifts much smaller than the average thermal energy, ha> < kT, albeit special precaution is necessary when the system forms van der Waals dimers [302]. 

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