There are two differences between the interference effects observed at ±2.23eV in butane and the interference feature at 0eV in meta-substituted benzene. Firstly, the non-interfering contributions from the two orbitals in butane are unequal, whereas they are equal in metasubstituted benzene. Secondly, the interference feature in meta-substituted benzene is midway between the occupied and virtual orbitals, that is, midway between the orbitals that interfere destructively, whereas for butane the interference feature appears at an energy above/below the pairs of occupied/virtual orbitals that are dominant.