Here, it should be recalled that at low temperatures, it is a well known fact that C 3 is a more stable carbon cluster when compared to C 2 and C 4 which reaffirms the fact that the CEA database for larger carbon cluster is extremely inaccurate especially at high temperatures. Apart from this behavior, overall, there is significant difference in the mole fractions of the C 4 molecule which affects the composition of the whole mixture leading to differences in mole fractions for other molecules like C 2 . These differences are again attributed to the differences in the thermodynamics data of the molecules being studied. This equilibrium calculation is done for a pure acetylene vapor at a pressure of 1 atm. The species considered for this calculation are the ones listed in Table . It should be recalled that the thermodynamic properties of all these molecules have been calculated in this work using the W1 method. The inspiration of using an acetylene vapor is from the shock tube experiments done by Shinn and Park in the 1980s to study the optical properties of C 3 and C 2 H. Although the experiments used a mixture of 99% Argon and 1% C 2 H 2 at an initial pressure of 0.76 kPa, we do not use the same conditions since the aim of this calculation is to see the relative mole fractions of various carbon clusters and hydrocarbons. Looking at the filtered view of the equilibrium calculations, it is evident that C 2 , C 3 , C 4 and C 4 H are important species especially when considering their impact on absorption of radiation in the boundary layer. The mole fractions of these four species is non-negligible and in future, we wish to quantify the amount of radiation absorption that these molecules would lead to using coupled CFD-Radiation calculations.