Limits on the asymmetry parameters for two- and three-photon photofragmentation.
The known constraint, -1 </= beta </= 2, on the asymmetry parameter for single-photon photofragmentation is generalized to two-photon fragmentation, either with a cylindrically symmetric laser field or with crossed linear polarizations, and to axially symmetric three-photon fields. It is shown that the angular distribution in both two-photon cases is characterized by two independent parameters. Physically accessible regions of the parameter planes are established, and the forms of the angular distributions at special points are discussed. The results are compared with recent predictions concerning the angular distributions arising from prompt photodissociation by various two- and three-photon excitation schemes.
Physical and Theoretical Chemistry Laboratory, Chemistry Department, University of Oxford, South Parks Rd, Oxford, UK OX1 3QZ.
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