Strong-field approximations for the orientation dependence of the total ionization of homonuclear diatomic molecules with different internuclear distances

We investigate the orientation dependence of ionization of homonuclear diatomic molecules with different internuclear distances numerically and analytically. For molecules with small internuclear distances, the predictions of the usual theoretical models arising from strong-field approximation (SFA), where only the contribution of the ground state to ionization is considered, match the results obtained by the numerical solution of the time-dependent Schrödinger equation (TDSE). For molecules with intermediate and large internuclear distances, the predictions of the usual SFA theoretical models show the important difference with the TDSE results. For these cases, the excited state plays an important role in the angle-dependent ionization of molecules. We develop the SFA models to consider the important contributions of excited states to ionization of molecules.