Effective Dipole Moment of Rotational Transitions of X₂Y Molecules

Contributions determining the rotational dependence of the effective dipole moment of molecules are calculated for the ground state of H ₂S and H₂O molecules. The calculation is carried out in various ordering algorithms of perturbation theory. It is shown that the convergence of the effective dipole moment for the ground state of an H ₂O molecule in the polynomial representation is rather slow in the rotational operator /. (the convergence radius is K* ≤17). Nonpolynomial forms of the dipole moment as a function of rotational operators are discussed.