Quantum rotational states of PF3 molecule pair on Ru(0 0 1) surface

The azimuthal angular distribution of PF3 molecules on Ru(0 0 1) could be semi-quantitatively explained down to a temperature of 20 K by considering that the molecules form a classical gear network on a triangular lattice under the influence of a simple model potential. The limitations of such a treatment are clarified by analysing the quantum rotational states of a PF3 molecule pair on Ru(0 0 1). The quantum rotational states are calculated numerically on an adiabatic potential energy surface obtained through ab initio molecular orbital (MO) calculations. The temperature at which the quantum effects become appreciable is estimated. The quality of the simple model potential is also examined in comparison with the potential obtained through MO calculations.