Showing papers by "Ugo Fano published in 1972"

Angular momentum transfer in the theory of angular distributions.

Abstract: The angular distribution of collision products is expressed as a sum of incoherent contributions corresponding to different magnitudes of the angular momentum ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{j}}}_{t}$ transferred to an unpolarized target. For targets with a characteristic internal reference frame (e.g., molecules) the coefficients of this sum are interpreted as generalized ${2}^{j}t$-pole polarizabilities of the target in its internal reference frame, analogous to the scalar and quadrupole polarizabilities that determine the Raman effect. The theory is developed in the context of photoionization, but is applicable to more general collision processes as well. It is illustrated by use and extension of diagrammatic techniques.

Theory of Electron-Molecule Collisions by Frame Transformations

Abstract: Laboratory-frame and body-frame treatments are combined using the $l$-uncoupling transformation which had served to interpret the absorption spectrum of ${\mathrm{H}}_{2}$. Application of a phase-amplitude procedure converts the Schr\"odinger equation to a Volterra-type integral form, which reduces to a Born-like approximation when the long-range interactions are weak. Attention is directed to features of low-energy collisions that must be considered by a realistic theory. This paper develops a formalism that can take advantage of different simplifying factors in different ranges of the electron-molecule distance. Detailed developments and applications are deferred.

Parity Unfavoredness and the Distribution of Photofragments

Abstract: The angular distribution of photodisintegration products, previously resolved into contributions with different angular momentum transfers ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{j}}}_{t}={\stackrel{\ensuremath{\rightarrow}}{\mathrm{j}}}_{\ensuremath{\gamma}}\ensuremath{-}1$, is analyzed further according to the parity of ${j}_{t}$. Odd values of ${j}_{t}+{j}_{\ensuremath{\gamma}}+l$ correspond to parity-unfavored transitions which result from effectively pseudotensor interactions with the unobserved fragments. In electric dipole processes, these transitions yield an angular distribution with the fixed asymmetry parameter ${\ensuremath{\beta}}_{\mathrm{unf}}=\ensuremath{-}1$ while the distribution of parity-favored transitions consists of three standard functions weighted by dynamical factors.