Calculation of the electronic spectrum for Ar-OH

We calculate the rovibrational structure for the electronic transition of the Ar-OH complex between the ground and first excited electronic states, which correlate asymptotically with Ar(1S0)+OH(X 2?) and Ar(1S0)+OH(A 2?+), respectively. An ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex. The calculated spectrum is compared with experimental results. In the low-frequency region the spectrum is found to be well ordered and assignment of spectroscopic features in terms of bending and stretching quantum numbers is possible. Close to dissociation, bend-stretch coupling leads to highly mixed states for which such assignments are no longer possible.