Pressure broadening theory of assymmetric-top molecules using the methods of irreducible tensor operators

Contributions to the second-order collision efficiency function used in Anderson and Murphy-Boggs pressure-broadening theories due to dipole-dipole, dipole-quadrupole, quadrupole-dipole, and quadrupole-quadrupole interactions are derived by the method of irreducible spherical tensor operators for molecules of arbitrary symmetry. Results are given explicitly in terms of dipole and quadrupole line strengths. General expressions for dipole line strength in the asymmetric rotor basis, as well as quadrupole moment line strength for the special case of molecules with two independent quadrupole moment components, are derived.