Role of symmetry in strong-field ionization of molecules

Angular distributions of photoelectrons, produced by single ionization of ethylene or benzene molecules with an intense linearly polarized laser field, are calculated. The anisotropy and the yield of the photoelectrons depend strongly on the orientation between the molecular geometry and the field. In particular, electron emission in nodal planes is suppressed. The orientational dependence, also found in the total ionization rate, is a consequence of the symmetry of the highest occupied molecular orbital.