On the effects of He+ ions bombardment of polyphenylacetylene

Polyphenyl acetylene (PPA) thin films deposited on silicon substrates have been bombarded with a beam of 30 keV of He+ ions. The radiation damage of the film has been monitored by FT-IR spectroscopy at fluences between 0.8 x 10(19) and 1.1 X 10(20) ions/m(2). The spectral changes undergone by the PPA film have been interpreted in terms of chain scission with formation of acetylenic and saturated end groups, and in terms of crosslinking reaction and extensive radiolytic degradation. The expected PPA cyclization reaction, a reaction which transforms a linear polymer into a ladder polymer has not been observed, although polystyrene (PS) is able to give this kind of reaction under somewhat similar conditions to those adopted in the present work. The results have been discussed in an astrochemical context in relation to the infrared emission spectra of certain astrophysical object and molecules present in the interstellar medium. (C) 2003 Elsevier Ltd. All rights reserved.