Suppression effect in the nonsequential double ionization of molecules by an intense laser field

The $S$-matrix theory is developed to study the nonsequential double ionization (NSDI) of diatomic molecules ${\text{N}}_{2}$ and ${\text{O}}_{2}$ in an intense field. It is shown that electronic structures influence the NSDI process of molecules. Compared to ${\text{N}}_{2}$, a suppression effect of NSDI of molecule ${\text{O}}_{2}$ is found and it can be explained by the difference between the angular distributions of the first ionized photoelectrons of ${\text{N}}_{2}$ and ${\text{O}}_{2}$. The ratios of the NSDI rate to the single-ionization rate are also obtained and compared with experimental observations.