Positronium in high temperature phases of long-chain even n-alkanes

• DOI: 10.1016/j.chemphys.2008.11.019
• Publication Date: 2008-11-28T05:19:31Z
• Authors: T. Goworek; M. Pietrow; R. Zaleski; B. Zgardzińska
• Keywords: Positronium; Alkane; Carbon fibers

Abstract Positron lifetime spectra were measured for a set of long-chain alkanes C n H 2 n +2 . Phase transitions in solid are usually visible as a change of ortho -positronium ( ortho -Ps) lifetime (and Ps formation probability). In the case of n -alkane molecules containing more than 25 carbon atoms in the chain, up to the longest in which the rotator phase exists ( n = 38), unexpectedly there is no change of ortho -Ps lifetime at the transition from the rotator to liquid. In the phase M appearing when the chains are still longer ( n ⩾ 36), the orth o-Ps lifetime is shorter and the step of lifetime at melting is again well visible. It indicates better degree of molecular order in M phase than in rotator one. At low temperatures the lifetime in the samples with n ⩾ 38 obtained by crystallization is shorter than in molten ones.