The partition sum of methane at high temperature

The total internal partition function of methane is revisited to provide reliable values at high temperature. A multi-resolution approach is used to perform a direct summation over all the rovibrational energy levels up to the dissociation limit. A computer code is executable on line at the URL: http://icb.u-bourgogne.fr/JSP/TIPS.jsp to allow the calculation of the partition sum of methane at temperatures up to 3000 K. It also provides detailed information on the density of states in the relevant spectral ranges. The recommended values include uncertainty estimates. It is shown that at the upper limit of 3000 K, the systematic error (underestimation) of previous calculations (HITRAN 2004) reaches −50% equivalent to a temperature error of the order of +200K.