Double photoionization of rotating linear molecules

This communication presents a theoretical study of the angular distribution of one or both of the two electrons emitted in one-photon, one-step double ionization of a linear molecule. Experiments which do or do not detect spin of the photoelectrons have been considered. Effects of molecular rotation on double photoionization have been studied in both Hund's coupling schemes (a) and (b) by using parity-adapted states. Selection rules obtained in this paper are very different from those derived earlier for single photoionization and for Auger decay following the absorption of a photon in a rotating linear molecule. It is shown that complete specification of the spin-unresolved and of spin-resolved angular distributions of both photoelectrons require, respectively, three and seven parameters which depend, among other things, on their energies as well as directions of emission. The approach developed in this paper has been used to analyze spin-unresolved double photoionization in the $3\sigma^2_g$ shell of the $\rm N_2$ molecule. The angular distribution is quite different depending on whether or not molecular rotation has been taken into account. Also, it is found to change significantly for different rotational transitions. Effects of electron-electron correlation are clearly manifested even in non-coincident, both rotationally resolved-as well as unresolved-double photoionization