PARTITION SUMS FOR NON-LOCAL THERMODYNAMIC EQUILIBRIUM APPLICATIONS: NLTE-PS

$^{a}$D. P. Edwards, M. L\'opes-Puertas, and R. R. Gamache J. Quant. Spectosc. Radiat. Transfer 59, 423-436, 1998.Author Institution: University of Massachusetts Lowell; Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts LowellFor 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: $H_{2}O$, $CO_{2}$, $O_{3}$, $N_{2}O$, $CO$, $CH_{4}$, $NO$, $NO_{2}$, and $OH$. The resulting data are fit to a polynomial expression of the form $Q(T) = a_{0} + a_{1} T + a_{2} T^{2} + a_{3} T^{3}$ 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)