Quantum Chemistry Study of Chemical Interactions in Rocket Plumes 4 th European Conference for Aerospace Sciences

The chemistry of rocket plumes and their interaction with the environment is becoming of greater interest as the number of launches is expected to increase. Conditions in the upper atmosphere are particularly challenging and combine low pressures with temperatures varying from that of the hot engine exhaust to the ambient environment. Chemical reaction mechanisms that perform reliably across an extended range of temperatures are hence required. The current study addresses the issue by investigating the interactions of selected species including hydrocarbons, particulates, nitrogen and sulphur under plume conditions through quantum mechanical methods. The intention is to provide a bridge to the chemistry of the surrounding atmosphere. Potential energy surfaces (PESs) were determined using composite G4 based methods. Low-pressure chemical kinetic parameters for the selected reaction steps were calculated using Rice-Ramsperger-Kassel-Marcus/master-equation (RRKM/ME) based approaches or an inverse Laplace transform (ILT) combined with high pressure literature data. Variational transition state theory (VTST) was also used to determine non-pressure dependent rates for exchange reactions with a clearly defined transition state. Rates were calculated over a wide range of temperatures and pressures representative of practical conditions. Updated thermochemistry was also produced for enthalpy, heat capacity, entropy and Gibbs free energy in the range 200 - 2000 K and fitted to standard JANAF polynomials.