Accurate high-pressure and high-temperature effective pair potentials for the systems N2–N and O2–O

Abstract

Statistical mechanical chemical equilibrium calculations of N2 and O2 show that these molecules dissociate behind strong shock waves. Our determination of accurate intermolecular potentials has required the consideration of the dissociation products N and O. Our previous theoretical efforts to predict the thermodynamic properties of these molecules relied in part on corresponding states theory and shock wave data of argon, without consideration of the dissociation products. Recent high-pressure Hugoniot measurements, however, allowed a more accurate determination of the potentials and the explicit inclusion of the dissociation products. The best fit to the data is obtained with the exponential-6 coefficients, for O2–O2: ε/k=125 K, r*=3.86 Å, α=13.2; for O–O: ε/k=700 K, r*=2.40 Å, α=11.0; for N2–N2: ε/k=293 K, r*=3.91 Å, α=11.5; and for N–N: ε/k=600 K, r*=2.47 Å, α=10.0. The unlike pair interactions are obtained from these like interactions with a modified Lorentz–Berthelot rule. The coefficients in the modified Lorentz–Berthelot equations are k/l/m=1/1/0.93 for O2–O– and k/l/m=1/1/0.90 for N2–N interactions.