Orientational averaging in the intense field tunnel ionization of molecules

The effect of molecular structure and orientation on the rate of tunnel ion ization in intense laser fields is considered for linear molecules. The non spherical nature of the molecular electrostatic potential near the classica l electron turning point results in a nonisotropic distribution of tunnelin g rates. This must be considered when determining the overall ionization ra te of a randomly oriented ensemble. Calculations are performed for two atom :molecule test pairs with similar ionization potential, Ar:N-2 and Xe:O-2, and the results are compared to experiments [Talebpour, Chien, and Chin, J. Phys. B 29, L677 (1996); Guo , Phys. Rev. A 58, R4271 (1998)]. (C) 2000 Am erican Institute of Physics. [S0021-9606(00)00322-6].