Effect of breaking cylindrical symmetry on photoelectron angular distributions resulting from resonance-enhanced two-photon ionization

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Abstract
An expression is derived for the photoelectron angular distribution (PAD) following (1+1’) resonance‐enhanced multiphoton ionization (REMPI) of a molecule with linearly polarized light beams. When the two polarization vectors are parallel, cylindrical symmetry exists, and the PAD depends only on θ, the angle between the linear polarization vector of the ionizing radiation and the electron ejection direction. When the polarization vectors are perpendicular, cylindrical symmetry is broken, and the PAD shows φ and θ dependence. For an arbitrary angle between the two polarization vectors, the angular distribution ceases to have reflection symmetry. This breaking of cylindrical symmetry causes interference effects in the REMPI process that are readily described using a density matrix formalism. As an example, the (1+1’) REMPI of NO via its A 2Σ+ state is considered.