Rotations of molecular photoelectron angular distributions in above threshold ionization of H2+ by intense circularly polarized attosecond UV laser pulses

Abstract

We present molecular photoelectron angular distributions (MPADs) in multi-photon ionization processes by circularly polarized attosecond UV laser pulses. Simulations are performed on the single electron aligned molecular ion H by solving corresponding 3D time-dependent Schrödinger equations. Numerical results of molecular above threshold ionization (MATI) show that rotations of MPADs with respect to the molecular and polarization axes depend on pulse intensities and photoelectron kinetic energies. We attribute the rotation to Γ, the difference between parallel and perpendicular ionization probabilities. It is found that in a resonant ionization process, the rotation angle is also a function of the symmetry of intermediate electronic states. The coherent population transfer between the initial and the resonant electronic states is controlled by pulse intensities. Such dependence of rotations on the pulse intensity is absent in Rydberg resonant ionizations as well as in MATI at large energy photons ℏω > Ip, where ω is angular frequency of photons and Ip is the molecular ionization potential. We describe these processes by a multi-photon perturbation theory model. Effects of molecular alignment and pulse ellipticities on rotations are investigated, confirming the essence of the ionization parameter Γ in rotations of MPADs.