Fig. 3

Photoelectron angular distributions and β parameters. a and b represent two photoelectron angular distributions (PAD) in polar coordinates for electron kinetic energies corresponding to HH17 and SB16, respectively, as measured in the ETH experiment with the reaction microscope detector. The green solid lines are the fit of Eq. 1, multiplied by sin(θ) to account for the detector geometry, to the data. c Values of β₂ parameter as a function of photon energy sampled at the harmonic (solid line) obtained in the ETH (in red) and Lund (in blue) experiments. The black dots are taken from³³ and the arrows at 26.6 eV and 28 eV indicate the positions of the 3s→4p and the 3s→5p autoionization resonances. d Values of β₂ parameter (solid lines) and β₄ parameter (dashed lines) as a function of photon energy sampled at sideband energy positions for the ETH (in red) and Lund (in blue) experiments. In panels c and d, the data represent the mean value extracted by independent datasets, while the error bars indicate the standard deviation