ROTATIONAL EFFECTS IN PHOTOIONIZATION: BRIDGING THE GAP FROM MICROVOLTS TO KILOVOLTS

Abstract

We have performed the first measurements of photoion rotational distributions over an extended range $(e.g., 0 \leq E_{k} \leq 200 eV for N_{2}).^{1}$ We generated these data by exploiting dispersed fluorescence detection. The molecules are ionized using radiation from the LSU CAMD synchrotron source. We detect rotationally resolved fluorescence from ${N_{2}}^{+}$ and $CO^{+}$. The detection bandwidth is uncoupled the excitation bandwidth in such measurements, and this permits investigations into aspects of molecular scattering dynamics that would be otherwise inaccessible. An escaping photoelectron traverses the field of the molecular photoin as it exits, and as it scatters from this anisotropic potential, the angular momentum of the residual ion can change. Conversely, rotationally resolved data are useful for studying the scattering dynamics. $N_{2}$ and CO exhibit striking differences in their photoejection dynamics, and the energy dependence of the distributions extends deep into the ionization continua. Agreement between experiment and theory is $excellent.^{1}$ As a complement to these rotationally resolved studies, we have also measured fluorescence polarization from the photoions, and these measurements of rotational alignment serve as a useful probe which is also suitable for ``global'' survey studies of the ionization $dynamics.^{2}$