At temperatures above 1500 K, the measured vapor pressure of sodium chloride at saturation exceeds that calculated for the sum of the NaCl monomer and the Na2Cl2 ring (rhombic) dimer. The difference is primarily a dimer together with higher polymers of linear or chain structure. This dimer has much higher entropy and enthalpy than the ring dimer. Approximate values are reported for the thermodynamic properties and for structure calculations using a potential function that is based on the spectra of the monomer and was adopted previously for the ring dimer.