Coulomb effects on strong-field ionization of stretched H2+

We numerically and analytically study ionization of H-2(+) with large internuclear distances R in strong elliptically polarized laser fields. Numerical simulations show that the offset angle in the photoelectron momentum distribution (PMD) is larger for cases of large R than for cases of H-2(+) with small R and model atoms with similar ionization potentials. In addition, the PMDs for cases of large R show clear interference patterns which disappear for cases of small R. By developing a strong-field model which includes the contributions of the first excited state and the Coulomb potential, we reproduce the phenomena for large R. Tunneling ionization of H-2(+) with large R involves a complex four-body interaction between the laser, the electron, and the two nuclei. Our model can approximate the four-body interaction as the three-body one and clearly identify the effects of charge resonance and different nuclei on tunneling ionization. Our work suggests a manner for probing complex interactions in strong-field ionization of stretched molecules with high time resolution.