Polynomial expression for calculating 'Total Internal Partition Sums' for portable gas sensors

Spectroscopic gas sensors rely on spectral data of molecules available from various databases for analysis of gases. The total internal partition sums (TIPS) for molecules is one of the essential parameter needed for analysis of gases using their absorption spectrum. The calculated values of TIPS are reported by many researchers and are available in tabulated form in HITRAN database. The database is useful in many industrial gas sensors. These sensors require fast response along with portability. However, storing and recalling the TIPS data adds to the computational cost and time. For such applications, a polynomial expression for recalling the TIPS values is a fast and convenient method. The present study provides the polynomial coefficients for TIPS as a function of temperature for the rapid recall of data listed in the HITRAN 2016. The entire temperature range 70–3000 K is covered in three sets of temperatures for polynomial fitting. The lowest-order polynomial expressions which can model the variation of TIPS with temperature with better than 1% accuracy are listed for 49 molecules (125 isotopologues) for the ease of recall. The coefficients of polynomials up to fifth order are also provided in supplementary material for applications requiring higher accuracy. The data will be useful in the research and development of spectroscopic gas sensing technology.