Photoionization of NO(A2Σ+, v=0,N) at 226 nm: ion-recoil momentum spectroscopy

We report the first observation of ion recoil induced by the ionization process for a molecule. The applicability of the method has been demonstrated by determining the β2 and β4 anisotropy parameters of the angular distributions of NO+ ions in the resonance-enhanced two-photon ionization of NO(X2Π1/2, v=0,J) via the A2Σ+(v*=0, N*) state at 226 nm. An energy resolution in the range of 10 μeV is demonstrated. The method might prove to be particularly useful for studying complex ionization-fragmentation processes as they occur for example for superexcited molecules.