摘要： Recently, in the tunneling regime of strong-field ionization an unexpected Coulomb field effect has been identified by numerical solution of the time-dependent Schr?dinger equation [Phys. Rev. Lett. 117, 243003 (2016)] in photoelectron spectra in the upper energy range of the direct electrons. We investigate the mechanism of the Coulomb effect employing a classical theory with Monte Carlo simulations of trajectories, and a quantum theory based on the generalized eikonal approximation for the continuum electron. The effect is shown to have a classical nature and is due to momentum space bunching of photoelectrons released not far from the peak of the laser field. Moreover, our analysis reveals specific features of the angular distribution of high-energy direct electrons, which can be employed for molecular imaging. For the H2+ molecule as an example we show the signatures of the molecule orientation and the molecular structure in the investigated angular distribution.