Rydberg molecules are systems with a single electron outside a stable closed-shell cation core . They have repulsive ground electronic states with only shallow van der Waals minima and stacks of bound Rydberg states. This feature makes them interesting for the construction of lasers. Thus there is continuing interest in the Rydberg spectra of diatomic rare-gas hydrides, since the first observation of the Rydberg spectra of ArH in 1970 , and in the spectra of H3.
Ab initio potential energy curves for electronic states of KrH and KrH +. (Petsalakis et al. J.Chem.Phys. 119 2004 (2003)
At TPCI, we employ the MRDCI method  to calculate the potential energy curves of the ground and excited electronic states of Rydberg molecules [4-7], their dipole transition moments, as well as the coupling matrix elements, radial and rotational-electronic. Subsequently radiative transition probabilities are calculated for bound-bound and bound-repulsive transitions. Predissociation widths are determined using the complex coordinate method developed at TPCI. All higher-lying Rydberg states, their vibrational levels and vibrational autoionization widths are determined from the ab initio data via Quantum Defect Theory calculations.
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 I.D.Petsalakis, G.Theodorakopoulos and R.J.Buenker, Theoretical ab initio study of the electronic states of KrH and KrH+..Quantum defect and complex coordinate calculations on the Rydberg states of KrH. J.Chem.Phys. 119 2004 (2003)
 I. D. Petsalakis, G. Theodorakopoulos,Yan Li, G.Hirsch,R.J.Buenker and M.S. Child,Theoretical study on the Rydberg states of NeH. Ab initio, quantum defect and complex coordinate calculations, J. Chem. Phys. 108,7607 (1998)
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