Ionic Angular Distributions Induced by Strong-Field Ionization of Tri-Atomic Molecules

Angular distributions of fragment ions from ionization of several tri-atomic molecules (CO_2, OCS, N_2O and NO_2) by strong 800-nm laser fields are investigated via a time-of-flight mass spectrometer. Anisotropic angular distributions of fragment ions, especially those of atomic ions, are observed for all of the molecules studied. These anisotropic angular distributions are mainly due to the geometric alignment of molecules in the strong field ionization. Distinct different patterns in ionic angular distributions for different molecules are observed. It is indicated that both molecular geometric structure and ionization channels have effects on the angular distributions of strong field ionization/fragmentation.