Fourth-order contributions to the rotational-vibrational matrix elements for diatomic molecules; application to the Fς′v(m) functions for CO

Abstract Using the rotational potential function expanded through the quartic term as a perturbation, and considering successively a quartic and a quintic dipole moment function, general expressions are obtained for the vibration-rotation matrix elements corresponding to the transitions vJ→ς′J′ with ς′ ⩽ v +5. The vibration-rotation interaction functions F ς′ v ( m ) are deduced for the transitions v→ς′ ( v =0, 10, 20 and ς′ ⩽ v +4) of CO from calculations including third then fourth-order contributions to the matrix elements. The results obtained for the coefficients of the quartic polynomials fitting these functions are compared and their validity is discussed.