ENERGY-DEPENDENCE OF PHOTOION ROTATIONAL DISTRIBUTIONS OF N2 AND CO

We present the first measurements of rotational distributions for phot oionization over extended energy ranges [0 less-than-or-equal-to E(k) less-than-or-equal-to 200 eV for N2 (2sigma(mu)-1) and of 3 less-than- or-equal-to E(k) less-than-or-equal-to 125 eV for CO (4sigma-1)]. The N2 and CO results show a strikingly unusual and different energy depen dence. Although differences are expected due to the absence of a cente r of symmetry in CO, detailed calculations reveal that this behavior a rises from the presence of Cooper minima in the photoelectron continuu m (ksigma(g)) in the case of N2 and from an f-wave shape resonance for 4sigma-1 photoionization in CO.