Since non-diffuse molecular orbitals （NMOs） are insensitive to environment，when molecules are adsorbed and not broken，the near edge structures involving NMOs will still resemble structures of corresponding free molecules. If we probe adsorbed molecules with polarized X-ray photons，relative intensities of photoabsorption spectra near molecular edges will be different for various geometric arrangement of X-ray polarization. Such features can be used to determine orientations of adsorbed molecules.