The Na2CN molecule has been detected in the vapor over a mixture of sodium metal and sodium cyanide by means of Knudsen effusion mass spectrometry. The ionization potential, IP(Na2CN+) = 4.9 +/- 0.2 eV, and the energy of dissociation into NaCN anh Na, D-0 degrees(NaCN-Na) = 24.8 +/- 1.6 kcal/mol, have been determined. The measured value of the dissociation energy indicates moderately strong bonding of sodium to the NaCN fragment, although theoretical calculations indicate a somewhat lower value of 17.4 kcal/mol. The experimental ionization potential agrees well with the theoretical value of 4.66 eV calculated for the vertical ionization. The lowest energy structures are planar with C-s symmetry. The two linear isomers are ca. 12 kcal/mol less stable and may be described as "electronomers" Na+(CN)Na--(.) and Na-.(CN)Na--(+). The molecule can be described as a salt of the Na-2(+) radical cation with the CN- anion, like the previously reported Li2CN molecule. The presence of the Na2+ unit justifies the term hypervalent for this system.