Multiple ionization of atomic and molecular iodine in strong laser fields

We compare the multiple ionization of atomic and molecular iodine using 100-fs laser pulses at 610 nm over a wide range of laser intensities (2 x 10(12) W/cm(2)-3 x 10(15) W/cm(2)). We show that the elongation of the molecular ion to a critical distance drastically enhances the multiple ionization probability of the molecule compared to that of the atom. In particular, the yield of the ten-times-ionized molecule is higher than that of the three-times-ionized atom around 10(14) W/cm(2). This observation supports recent theoretical work on the role of the electron localization in intense-field molecular ionization. Around 10(15) W/cm(2), the quintuple ionization of atoms is observed, whereas fast I2+ fragments arising from the I-2 Coulomb explosion are not further ionized, even with 300- or 500-fs laser pulses. This result supports the concept of molecule stabilization in strong laser fields.