Complete description of two-photon (1+1′) ionization of NO deduced from rotationally resolved photoelectron angular distributions

Time-of-flight photoelectron spectroscopy has been used to record energy-resolved photoelectron angular distributions (PADs) following (1+1′) resonance-enhanced multiphoton ionization (REMPI) of NO via the vi=1,Ni=22 rovibrational level of the A 2∑+ state. The PADs corresponding to single rotational states of the resulting molecular ion show a strong dependence on the change in ion core rotation ΔN(≡N+−Ni) and also on the angle between the linear polarization vectors of the two light beams. Broken reflection symmetry [I(θ,φ)≠I(−θ,φ)] is observed when the polarization vectors of the two light beams form an angle of 54.7°. A fit to the PADs provides a complete description of this molecular photoionization, namely, the magnitudes and phases of the radial dipole matrix elements that connect the intermediate state to the ‖lλ〉 photoelectron partial waves (Refs. 1 and 2). This information is then used to predict unobserved quantities, such as ion angular momentum alignment and the full three-dimensional form of the PADs.