Knowledge Bank

For high-altitude radiative transfer models, the importance of non-LTE corrections to the vibrational partition sum has been shown to be important with the differences in calculated radiance as large as 30% at 130 km in some $cases.a$ In order to apply this correction the rotational and vibrational partition sums must be determined separately. To facilitate this, rotational and vibrational partition sums are calculated in the temperature range 100 - 450K for a number of isotopomers of atmospheric molecules important in NLTE processes: $H2O$, $CO2$, $O3$, $N2O$, $CO$, $CH4$, $NO$, $NO2$, and $OH$. The resulting data are fit to a polynomial expression of the form $Q(T)=a0+a1T+a2T2+a3T3$ where the coefficients are determined by a simplex nonlinear minimization routine. The resulting coefficients can then be used in a FORTRAN program for rapid recall of the rotational partition sum. The method of calculation of $Q(T)$ for each isotopomer, convergence of the partition sum in each temperature range, the quality of the fit of the data, and comparisons with other work are discussed. The program NLTE-PS is available from the HITRAN website (http://www.hitran.com/) or from one of the authors (Robert$\_$Gamache@uml.edu).