Despite having the largest magnitude for the E, the 87 Rb-MeTS system is predicted by the ab initio computations to have the greatest effect on only the energy shift of the ground state of 87 Rb, with ethene or ethane having the largest effect on the excited state. This suggests that the magnitude of E along the approach coordinate is not the decisive factor for how the electronic states are influenced, but rather the differences in the local non-uniformity The lowering of the ground 1 2 A state follows coat molecules MeTs > ethene > ethane, where 1 2 A has undergone the largest (negative) shift for MeTS (Figure (a)). This may be a result of the favourable interaction between 87 Rb and MeTS that leads to a very shallow and broad potential energy curve for ground-state 1 2 A (Figure (a)) and the largest relative negative adsorption energy (Table ). The adsorption energy for the ground state follows the trend MeTs > ethene > ethane.