Determination of rotational alignment of N2+ B u+2 and CO+ B +2 following photoionization of N2 and CO

When a low-pressure (10-2-Torr) sample of N2 or CO is exposed to a beam of linearly polarized synchrotron radiation (18-34 eV), electronically excited molecular ions are formed whose subsequent unresolved emission is found to be partially polarized. The degree of polarization of the N2+ B u+2-X g+2 fluorescence (391 nm) and the CO+ B +2-X +2 fluorescence (220 nm) is studied as a function of the energy of the ionizing radiation from threshold to higher energies. This information determines the alignment of the photoion, which in the case of N2 must be corrected for depolarization caused by spin-rotation and hyperfine interaction. From the polarization of the fluorescence we deduce, the ratio of parity-unfavored to the sum of parity-favored contributions for photoelectron ejection. Comparison of the dynamical channel ratio with theoretical calculations for - and -photoelectron ejection shows poor agreement for N2 and fair agreement for CO.