When beta-nitrous oxide (Cmca N2O) is laser heated to between 2000 and 3400 K at high pressures (10-55 GPa), it disproportionates into an ionic form of dimeric nitrogen dioxide (NO+NO3-) and nitrogen. Raman spectra of the quenched products suggest that the ionic phase is stable to 55 GPa at ambient temperature but, upon subsequent heating at pressures below 30 GPa, further dissociates into nitrogen, oxygen, and other nitrogen-oxygen compounds. X-ray diffraction patterns of the ionic phase indicate that it has an orthorhombic structure (Z = 4, rho(0) = 2.69 g/cm(3)), similar to the aragonite phase of calcium carbonate. The results suggest that the primary driver for ionization is densification at high pressures, whereas dissociation between 10 and 30 GPa results from the combined effects of densification and entropy increases.