Positron annihilation lifetime spectra for n-nonadecane in nitrogen atmosphere were measured as a function of pressure and temperature and compared with similar results for argon atmosphere. The phase diagram constructed from the nitrogen data is essentially different from that for argon. Nonmonotonous dependence of the melting point on pressure, typical of argon, does not appear. Sample damage at solidi. cation is much smaller. The triple point rigid-liquid-rotator phase is estimated as ( 311 K, 70 MPa). (c) 2008 Elsevier B. V. All rights reserved.