Rotationally resolved photoionization: Influence of the 4σ→kσ shape resonance on CO^+ (B^2Σ^+) rotational distributions

We present experimental and theoretical results on rotational distributions of CO^+ (B^2Σ^+) photoions. Rotational distributions were determined for both the v^+=0 and v^+=1 vibrational levels following photoionization of cold (T_0≈9K) neutral CO target molecules. Data were generated using dispersed ionic fluorescence over a wide range of photoelectron kinetic energies, 0⩽E_k⩽120eV, which allows one to interrogate the ionization dynamics. This wide spectral coverage permits illustrative comparisons with theory, and calculated spectra are presented to interpret the data. In particular, the comparison between theory and experiment serves to identify the strong continuum resonant enhancement at hν_(exc)≈35eV in the l=3 partial wave of the 4σ→kσ ionization channel, as this feature has profound effects on the ion rotational distributions over a wide range of energy. Second, there are differences between the rotational substructure for the v^+=0 and v^+=1 vibrational levels. All of the experimentally observed features and trends are reproduced by theory, and the consequences of these comparisons are discussed