2-PHOTON SPECTROSCOPY BETWEEN STATES OF OPPOSITE PARITIES

Magnetic and electric dipole two-photon absorption (MED-TPA), recently introduced as a spectroscopic technique for studying transitions betw een states of opposite parities, is investigated from a theoretical po int of view. An approximation referred to as weak quasiclosure approxi mation is used together with symmetry adaptation techniques to calcula te the transition amplitude between states having well-defined symmetr y properties. Selection rules for MED-TPA are derived and compared to selection rules for parity-forbidden electric dipole two-photon absorp tion.