Computations on the infra-red spectra of triatomic molecules

"Computations on the Infra-red Spectra of Triatomic Molecules" is a write-up of two projects in the field of computational spectroscopy. The first is the calculation of the opacity of hot water vapour. The water molecule is one of the most important absorbers in the infra red spectrum and it has been studied at length. Perhaps surprisingly, there is little reliable data on hot water (above - 1000 K) available. The major source of experimental data is around twenty-five years old and is flawed. It is both inaccurate and imprecise. Another source for molecular data is the HITRAN database. The HITRAN data gives very accurate results for water at low temperatures but is unreliable at the higher temperatures encountered, for example, in the atmospheres of cool stars. It was clear that the available data for hot water was somewhat lacking. Since there is interest in modelling cool stellar atmospheres it was necessary to calculate a more comprehensive list of molecular data. The results of those calculations are presented including a comparison with the previously available sources of data. Subsequent developments in this area and possible future work are discussed. The second project is the calculation of an effective potential energy surface for the ground electronic state of nitrogen dioxide. Nitrogen dioxide has a somewhat unusual electronic structure which makes it a particularly interesting molecule. This also creates difficulties peculiar to nitrogen dioxide. Another reason for working on this molecule is that it is a significant atmospheric pollutant and absorber. There have been a number of attempts to determine an accurate ground state potential energy surface for nitrogen dioxide. These attempts are described and their deficiencies discussed. The method with which the new surface was determined is presented. Rovibrational calculations on the surface are compared with observations and possible future work is considered.