Effects of orbital symmetries in dissociative ionization of molecules by few-cycle laser pulses

We have measured angular distributions of ion fragments produced in dissociative double ionization of CO, CO{sub 2}, and C{sub 2}H{sub 2} by intense ultrashort laser pulses. This report extends similar recent studies of O{sub 2} and N{sub 2} to a wider set of molecules. We found that for sub-10-fs pulses of sufficiently low intensity the fragments' angular distributions for all studied molecules are determined by angular dependence of the first ionization step. Those experimental angular distributions were in good agreement with angular dependent ionization probabilities calculated with the molecular tunneling ionization theory. The measured angular distributions directly reflect the symmetry of the corresponding molecular orbitals. For higher laser intensities and longer pulse durations, dynamic alignment and postionization alignment start to affect the angular distributions and ion fragments are preferentially ejected along the laser-polarization direction.