Detector integrated angular distribution: Chemisorption-site geometry, axial-recoil photofragmentation, and molecular-beam orientation

The seemingly diverse problems of chemisorption site geometry, orientation of species in molecular beams, and the axial recoil of molecular photofragments can be analyzed by means of the dependence of photoexcitation on target orientation. Expressions are derived for this orientation dependence in terms of the electric-dipole excitation amplitudes of the target. For cylindrically symmetric targets a particularly simple single-parameter distribution $1+{\beta }_T{P}_2\left(cos{\theta }_T\right)$ is obtained, analogous to the Yang-theorem result $1+{\beta }_D{P}_2\left(cos{\theta }_D\right)$ familiar from random-molecule photoelectron angular distributions ($T$ denotes target, $D$ denotes detector). For targets of arbitrary symmetry the distribution has a maximum harmonic dependence of second order and is completely characterized by at most eight parameters in addition to the overall cross section. The special utility of elliptically polarized light is also discussed.