Predicting half-widths and line shifts for water vapor transitions on the HITEMP database

The HITEMP database1 provides molecular spectroscopic parameters for high-temperature modeling of the spectra of molecules in the gas phase. Currently there are 5 molecular species on the database; H2O, CO2, CO, NO, OH. For H2O there are now transitions that have rotational quantum numbers up to J=50 and many transitions where the vibrational quantum numbers and prolate and oblate limit pseudo-quantum numbers (Ka and Kc) are not known. Line shape parameters are not available for most of these transitions. We have developed a method to determine these line shape parameters for the 3 most abundant isotopologues of water based on the Semi-empirical approach of Jacquemart etal.2 and an algorithm that estimates the number of vibrational quanta exchanged in the transition. Thus, vibrational dependence of the line shape parameters, which has been found to be important for H2O3, is taken into account for many transitions. When the parameters are not available from this new algorithm, average half-widhts as a function of J” are determined from a polynomial fit of validated calculated data. The results of the new algorithm and the J-averaged half-widths are compared with the values found on the 2008 version of the HITRAN database.