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Strong shock wave interactions with ceramic material ceria (CeO 2 ) in presence of O 2 and N 2 gases were investigated using free piston driven shock tube (FPST). FPST is used to heat the test gas to very high temperature of about 6800-7700 K (estimated) at pressure of about 6.8-7.2 MPa for short duration (2-4 ms) behind the reflected shock wave. Ceria is subjected to super heating and cooling at the rate of about 10 6 K/s. Characterization of CeO 2 sample was done before and after exposure to shock heated test gases (O 2 and N 2 ). The surface composition, crystal structure, electronic structure and surface morphology of CeO 2 ceramic were examined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results obtained from the experimental investigations show that CeO 2 can withstand high pressure accompanied by thermal shock without changing its crystal structure. Reducible CeO 2 releases lattice oxygen making it possible to shift between reduced and oxidized states upon the interaction with shock heated gas. Due to such reaction mechanism, CeO 2 ceramic undergoes nitrogen doping with decrease in lattice parameter. Investigations reveal that CeO 2 retains its crystal structure during strong shock interaction, even at elevated pressure.

Thermal decomposition of 1,2-dichloroethane (1,2-DCE) has been studied in the temperature range of 1050-1175 K behind reflected shock waves in a single pulse shock tube. The unimolecular elimination of HCl is found to be the major channel through which 1,2-DCE decomposes under these conditions. The rate constant for the unimolecular elimination of HCl from 1,2-dichloroethane is found to be 10 13.98(0.80 exp(-57.8 ( 2.0/ RT) s -1 , where the activation energy is given in kcal mol -1 and is very close to that value for CH 3 CH 2 Cl (EC). Ab initio (HF and MP2) and DFT calculations have been carried out to find the activation barrier and the structure of the transition state for this reaction channel from both EC and 1,2-DCE. The preexponential factors calculated at various levels of theory (HF/6-311++G**, MP2/6-311++G**, and B3LYP/6-311++G**) are (≈10 15 s -1 ) significantly larger than the experimental results. If the torsional mode in the ground state is treated as free internal rotation the preexponential factors reduce significantly, giving excellent agreement with experimental values. The DFT results are in excellent (fortuitous?) agreement with the experimental value for activation energy for 1,2-DCE while the MP2 and HF results seem to overestimate the barrier. However, DFT results for EC is 4.5 kcal mol -1 less than the previously reported experimental values. At all levels, theory predicts an increase in HCl elimination barrier on β-Cl substitution on EC. † Part of the special issue "Donald Setser Festschrift".

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A miniature three-component accelerometer balance system for measuring the fundamental aerodynamic force coefficients over blunt bodies has been designed, fabricated and tested in the Indian Institute of Science hypersonic shock tunnel HST2 at a nominal Mach number of 5.75. The model and the balance system are supported by rubber bushes, thereby ensuring unrestrained free-floating conditions of the model in the test section during the flow duration. Exhaustive axisymmetric finite-element simulations are carried out to select appropriate rubber bushes and materials for the model and the balance system. The internally mountable accelerometer balance is used to measure the drag, lift and pitching moment coefficients for a 60 • apex angle blunt cone within the effective tunnel test time of 800 µs. The measured aerodynamic force coefficients match very well with the theoretical values predicted using modified Newtonian theory at moderate specific enthalpy levels of the test gas.

Thermal decomposition of propargyl alcohol (C3H3OH), a molecule of interest in interstellar chemistry and combustion, was investigated using a single pulse shock tube in the temperature ranging from 953 to 1262 K. The products identified include acetylene, propyne, vinylacetylene, propynal, propenal, and benzene. The experimentally observed overall rate constant for thermal decomposition of propargyl alcohol was found to be k = 10((10.17 ± 0.36)) exp(-(39.70 ± 1.83)/RT) s(-1). Ab initio theoretical calculations were carried out to understand the potential energy surfaces involved in the primary and secondary steps of propargyl alcohol thermal decomposition. Transition state theory was used to predict the rate constants, which were then used and refined in a kinetic simulation of the product profile. The first step in the decomposition is C-O bond dissociation, leading to the formation of two important radicals in combustion, OH and propargyl. This has been used to study the reverse OH + propargyl radical reaction, about which there appears to be no prior work. Depending on the site of attack, this reaction leads to propargyl alcohol or propenal, one of the major products at temperatures below 1200 K. A detailed mechanism has been derived to explain all the observed products.