Effective dipole-moment operator for nonrigid H₂X-type molecules. Application to H₂O

A theory of the transformed dipole moment operator for nonrigid H₂X-type molecules has been worked out using the method of contact transformation. The treatment takes into account the large amplitude bending motion, which is described by the coordinate ρ{variant}. Formulae obtained for the transformed dipole moment operator for bending vibration quantum bands and for combination bands have been used for the determination of the functions μ^e_x(ρ{variant}), μ¹_x(ρ{variant}) and μ³_z(ρ{variant}) from the expansion of the molecular fixed component μ_α(ρ{variant}, q) (α = x, y, z) of the electric dipole moment of the H₂O molecule over q normal coordinates. Some different model forms for this function have been used.