Theory of molecular dissociation in shocked nitrogen and oxygen
Recent measurements provide evidence for shock-induced dissociation in molecular nitrogen and oxygen. Nitrogen shows a dramatic increase in compressibility above about 30 GPa, with densities in the range expected for a monatomic fluid. This effect is much less obvious in the oxygen data, but it is reasonable to assume that dissociation occurs in that case as well. Static measurements on the solid show no evidence of a transition from a molecular to a monatomic form in nitrogen up to 52 GPa or in oxygen up to 13 GPa. Calculations by McMahan and LeSar predict the transition to occur at about 100 GPa in solid nitrogen. Hence, high temperatures are believed to drive shock-induced dissociation. In this paper, we use a chemical equilibrium model to explain the shock experiments. The fluid is taken to be a mixture of the molecular and monatomic species. The equation of state (EOS) for this mixture is computed from EOS for the pure molecular and monatomic fluids, assuming ideal mixing. The equilibrium composition, or degree of dissociation, is determined by minimizing the free energy at constant temperature and pressure. For the molecular species, we use EOS described previously, that have been shown to agree with experimental data in the regime where no dissociation occurs. EOS for the monatomic fluids are discussed below. Our predictions of the shock data are most sensitive to two aspects of the EOS for the monatomic species - the binding energy and the electronic statistical weight. 13 refs., 4 figs.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5488507
- Report Number(s):
- SAND-85-0438C; CONF-850736-31; ON: DE85015148
- Resource Relation:
- Conference: American Physical Society topical conference on shock waves in condensed matter, Spokane, WA, USA, 22 Jul 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
NITROGEN
DISSOCIATION
OXYGEN
BINDING ENERGY
DENSITY
DISSOCIATING GASES
EQUATIONS OF STATE
FREE ENERGY
ISOTHERMS
SHOCK WAVES
THEORETICAL DATA
DATA
ELEMENTS
ENERGY
EQUATIONS
FLUIDS
GASES
INFORMATION
NONMETALS
NUMERICAL DATA
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
400201* - Chemical & Physicochemical Properties