Recent work: I .D. Petsalakis, D. Tzeli and G. Theodorakopoulos, Theoretical study on the electronic states of NaLi. J. Chem. Phys. 129, 054306 (2008), I. D. Petsalakis and G. Theodorakopoulos, Multireference configuration interaction and quantum defect calculations on the Rydberg states of the BH molecule. Mol. Phys. 104,103 (2006)

It is virtually impossible to calculate highly excited electronic states of molecules by ab initio methods. However, the ab initio data can form the basis for an extrapolation to the entire Rydberg spectrum of a molecule via Multi Channel quantum Defect Theory (MQDT). The scaling features of the MQDT theory lead to good approximations for the potentials of the whole manifold of states, from the lowest-lying ab initio potential energy surfaces:

Rydberg states of ^{1}A_{1} symmetry of H_{2}O, generated from MQDT functions (solid lines) and from ab initio calculations (solid (for data employed in the fit) and open circles)

I. D. Petsalakis G. Theodorakopoulos and M.S. Child, Ab initio multichannel quantum defects for the ^{1}A_{1} Rydberg states of H_{2}O. J.Phys. B 28 ,5179 (1995), G. Theodorakopoulos, I.D.Petsalakis and M.S.Child, On the construction and use of ab initio quantum defect functions for H_{2}O. J. Phys B 29, 4543 (1996)

Vibrational perturbations in the Rydberg specta as well as vibrational autoionization widths of levels of Rydberg states lying above vibrational levels of the ion, can be calculated from the quantum defect functions

Autoionization of vibrational levels of the nd states of NO _{2}, lying above the 001 level of NO _{2}^{+}

I.D.Petsalakis, G.Theodorakopoulos and M.S.Child, The Rydberg states of NO_{2}. Vibrational autoionization of the ndó states. J.Chem.Phys. 115,10394 (2001)