ACCURATE HIGH-PRESSURE AND HIGH-TEMPERATURE EFFECTIVE PAIR POTENTIALSFOR THE SYSTEMS N-2-N AND O-2-O

Statistical mechanical chemical equilibrium calculations of N-2 and O- 2 show that these molecules dissociate behind strong shock waves. Our determination of accurate intermolecular potentials has required the c onsideration of the dissociation products N and O. Our previous theore tical efforts to predict the thermodynamic properties of these molecul es relied in part on corresponding states theory and shock wave data o f argon, without consideration of the dissociation products. Recent hi gh-pressure Hugoniot measurements, however, allowed a more accurate de termination of the potentials and the explicit inclusion of the dissoc iation products. The best fit to the data is obtained with the exponen tial-6 coefficients, for O-2-O-2: epsilon/k=125 K, r=3.86 Angstrom, a lpha=13.2; for O-O: epsilon/k=700 K, r=2.40 Angstrom, alpha=11.0; for N-2-N-2: epsilon/k=293 K, r=3.91 Angstrom, alpha=11.5; and for N-N: epsilon/k=600 K, r=2.47 Angstrom, alpha=10.0. The unlike pair interac tions are obtained from these like interactions with a modified Lorent z-Berthelot rule. The coefficients in the modified Lorentz-Berthelot e quations are k/l/m=1/1/0.93 for O-2-O- and k/l/m=1/1/0.90 for N-2-N in teractions. (C) 1996 American Institute of Physics.