Alignment-free Molecular Frame Tunneling Probabilities

Tunneling ionization from a molecule in a strong laser field depends on the angle between the molecule and the electric field. This fact reflects the structure of the molecular orbital the electron tunnels from. We introduce a new method to measure the angular ionization probability of a small molecule in a strong field without actively aligning the molecule. Using COLTRIMS we have measured the angular ionization probability in the molecular frame of H$_2$ molecules. We find a considerable deviation from predictions made in established theories. We have also applied this technique to a small heteronuclear molecule. There we find evidence for tunneling from a lower lying molecular orbital.