Variational methods for the calculation of rovibrational energy levels of small molecules

Abstract

Variational rovibrational calculations performed on the molecules H₂O and CH⁺ ₂ are discussed with a view to pin-pointing the best solution strategy for each system. While all the methods discussed appeared to be reliable for the low-lying levels of water, CH⁺ ₂ has proved a more testing system. A recently proposed method for calculating highly rotationally excited states is applied to the J= 10 levels of CH⁺ ₂. Comparison of these calculations with those of Carter and Handy suggests that at this level of rotational excitation it will be necessary to consider full rovibronic coupling effects in the characterisation of any spectra of this floppy system.