Selection Rules and Linestrength Factors for Multiphoton Transitions in Gas Phase Molecular Spectroscopy
Journal of Chemical Physics
Multiphoton transitions are discussed in terms applicable to experimental spectroscopy. A simple tensor operator for the equations governing multiphoton transitions in molecules is obtained. Selection rules for these processes are derived by symmetry considerations and procedures for calculation of rotational line-strength factors are given. For the general transition, the rovibronic n-photon selection rules can be determined by the symmetry product of a n-photon operator with the rovibronic wavefunctions. The line-strength factors are found by considering the integral over rotations of the nth rank tensor operators. The line-strength evaluations do not depend on exact knowledge of the vibronic overlap, to within a constant factor.
Selection Rules and Linestrength Factors for Multiphoton Transitions in Gas Phase Molecular Spectroscopy Stephen E. Bialkowski and William A. Guillory Chemical Physics 55 229 1981