Numerical calculations of level shifts and power-broadening linewidths for double-photon absorption in truncated rigid-rotor models are presented. This work demonstrates the feasibility of a previously suggested calculational method. It is shown that level shifts in double-photon absorption deduced from three-state models are misleading since other states dipole-coupled to states directly involved in the transition make important contributions to the shifts.

• Received 1 December 1975

DOI:https://doi.org/10.1103/PhysRevA.15.1636