Momentum distributions of symmetric (H2+) and asymmetric (HeH2+) molecular ions in a circularly polarized laser field under different ionization mechanisms

Abstract

Abstract By numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE), we present photoelectron momentum distributions (PMDs) and photoelectron angular distributions (PADs) of symmetric ( H 2 + ) and asymmetric (HeH2+) molecular ions in circularly polarized (CP) laser pulses. By adjusting the laser wavelength, two circumstances of resonance excitation and direct ionization were considered. The ionization mechanism of the resonance excitation was mainly investigated. The results show that the PMDs of H 2 + and HeH2+ in the y-direction gradually increase with increasing intensity, and the number of PMDs lobes is in good agreement with the results predicted by the ultrafast ionization model. In the resonance excitation scenario, the PMDs of H 2 + are dominated by two-photon ionization, whereas the PMDs of HeH2+ are dominated by three-photon ionization. Furthermore, the PMDs of HeH2+ are stronger in the resonance excitation scenario than those of H 2 + , which can be explained by the time-dependent population of electrons. In addition, the molecular structure is clearly imprinted onto the PMDs.