to the PADs obtained from the photoelectron images within the narrow energy range of the transition. In eqn (1),  is the angle between the photoelectron velocity vector and laser polarization direction in the laboratory frame, 𝐼 𝜃 is the angle-dependent transition intensity, i.e. the PAD,  is the total cross-section at the kinetic energy being studied, 𝑃 is the second-order Legendre polynomial, 𝑃 cos 𝜃 3 cos 𝜃 1 , and 𝛽 is the anisotropy parameter, whose allowed values range from -1 for a purely perpendicular transition to +2 for a purely parallel transition. The resulting 𝛽 values are plotted with respect to eKE in Fig. (a).