CASSCF AND MULTI-REFERENCE CI CALCULATIONS OF INFRA-RED BANDSTRENGTHS FOR HCN

Author Institution: Department of Chemistry, University of Oslo; Institute of Theoretical Physics, University of Stockholm; Research Institute of Physics, University of Stockholm; Department of Astronomy, University of UppsalaTransmissions giving rise to combination bands in the region $5000-10000 cm^{-1}$ are expected to be the most important for calculations of stellar model atmospheres. This contribution will present a detailed study of such bands for the HCN molecule. Using MCSCF and CI methods, the potential energy surface around the equilibrium geometry has been investigated. In addition to frequencies, the dipole intensities have been calculated for all transitions among a total of 150 vibrational states up to about $15000 cm^{-1}$. It is found that the numerous weak transitions are as important as the few strong ones in determining the structure of stellar atmospheres