Double ionization of C2H4 and C2H6 molecules irradiated by an intense femtosecond laser field

We report experimental studies of double ionization of C2H4 and C2H6 molecules irradiated by 810 nm, 130 fs pulses at intensity of 1015-1016 W/cm2. The laser intensity dependent ratios X2+/X+ (X denoted C2H4 or C2H6) are measured for both linearly polarized and circularly polarized lights to determine the double ionization mechanism. The result is contrary to the prediction of the rescattering model, which demonstrates that the molecular structure should be taken into account to deal with the nonsequential double ionization of molecules.