Recoil frame photoelectron angular distributions in core O 1s ionization of H ₂CO

Recoil frame photoelectron angular distributions (RFPADs) from core O 1s ionization of H ₂CO are studied theoretically and experimentally. Time-dependent density functional theory calculations are performed to elucidate the ionization dynamics. The effect of averaging around the fragmentation axis is considered to explain differences between molecular frame and recoil frame angular distributions. Convolution by acceptance angles is also considered for the comparison between theory and experiment. The shape resonance to the virtual valence σ* (C-O) is properly reproduced by the calculations. In addition, it is found that the shape resonance plays a major role in assessing the RFPADs for light polarization parallel to the fragmentation axis.