Effect of orbital symmetry on the orientation dependence of strong field tunnelling ionization

In the strong field molecular tunnelling ionization theory (Tong X M 2002 Phys. Rev. A 66 033402), the ionization rate depends on structure parameters of molecules which can be extracted from molecular wavefunctions in the asymptotic region. By using molecular orbitals obtained from standard quantum chemistry packages, we extract these parameters for several selected nonlinear polyatomic molecules. We show that the symmetry properties of the molecular orbital are reflected vividly in the angle-dependent tunnelling ionization rates. The structure parameters for 17 nonlinear molecules have been calculated and tabulated for future applications. (Some figures in this article are in colour only in the electronic version)