Simulation of flows in shock-tube facilities by means of a detailed chemical mechanism for nitrogen excitation and dissociation
A database was recently developed at NASA Ames Research Center for the dissociation and excitation rates of the rovibrational energy levels of nitrogen. This work is a first step toward the development of a simplified mechanism for 3-D simulations of atmospheric entry flows. First, we have derived a Boltzmann average dissociation rate based on rotational and vibrational temperatures. At thermal equilibrium, a very good agreement is obtained with the rate proposed by Park (1990). Significant discrepancies are observed in thermal non-equilibrium conditions. Then, we have developed a 0-D vibrational state-to-state collisional model to simulate a typical shock in a nitrogen flow based on vibrational-specific excitation and dissociation reaction rates derived by assuming a Boltzmann distribution of the rotational energy levels at the translational temperature. We have shown that the vibrational energy relaxation for the monoquantum excitation processes deviates significantly from the conventional Landau-Teller law. The dissociation process, coupled with the energy level relaxation dynamics, strongly depends on multi-quantum jump processes. Finally, we have implemented the multi-temperature dissociation rate in a 1-D code for shock-tube flows and have compared our results with experimental results.
N-N2 state to state vibrational-relaxation and dissociation rates based on quasiclassical calculations
Abstract A complete set of V–T (vibration–translation) relaxation rates and of dissociation coefficients for the system O–O2 have been obtained by using quasiclassical trajectories on the Varandas and Pais potential energy surface. The results, averaged on a Boltzmann rotational distribution, cover the whole range of the vibrational ladder and are reproduced in closed form ready to be implemented in state-to-state kinetic models. The accuracy of the results has been tested by comparing them with available experimental and theoretical values (ASI-CAST project is acknowledged).
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)