Progress toward the reconstruction of molecular radial electron densities on the example of methane 2a1 and 1t2

The approach of photoemission orbital tomography (POT), i.e., the orbital density reconstruction from photoemission of planar molecular layers, is applied to measurements of the partial cross section from gas-phase methane (CH₄). Within a central-field and one-electron model, the method previously validated on neon is tested on CH₄'s molecular orbitals 2a₁ and 1t₂ with the goal to reconstruct absolute radial orbital densities. The reconstruction method is based on a Markov chain Monte Carlo optimization method, employing Bayesian inference, which additionally offers a reliable uncertainty evaluation. Applying the method to CH₄, we aim to bridge the gap between simple single atoms and molecular layers, and to find a practical reference standard for the determination of orbital densities within POT.