The past few years have marked phenomenal progress in the development of accurate quantum chemistry methods, so much so that their accuracy is comparable or better than the corresponding experiments. Consequently, an important outcome has been in the advancement of ab-intio calculations of thermochemistry data. In the current study, we utilize these quantum chemistry methods in three different ways as part of a larger effort to characterize the gaseous environment surrounding the spacecraft during atmospheric entry. To start off, we compute the formation enthalpies of the carbon clusters and hydrocarbons present in the boundary layer of an ablating heat shied. Second, we use these methods to obtain free energy and entropy to compute the equilibrium composition of these gases at relevant conditions and finally, the electronic absorption spectrum of these molecules are computed to identify candidates that can play a role in mitigating the radiative heat flux that impinges on the vehicle. This includes computing the excitation energies between the ground and excited electronic states and the electronic transition dipole moments between these states in order to identify strong absorption and emission transitions.