A search for trapped cations formed by condensation reactions between pentane radical cations and different neutral alkanes in solid matrices at 77 K

Irradiation with gamma rays of different alkanes (viz. heptane, octane, decane, 2-methylheptane, 2-methyloctane and 4-methyloctane), at low concentration in pentane and 1,1-difluorotetrachloroethane matrices at 77 K, results in the appearance of one single broad absorption band, which is due to the radical cations of the alkane solutes. Pure spectra of the electronic absorption of these radical cations are obtained by spectral deconvolution. The spectral shape and position of the bands obtained are compared with those of heavier ions, viz. radical cations of different tridecanes. The results obtained specifically rule out the presence in the irradiated pentane systems of trapped condensation ions, formed by direct ionic condensation (R1H+ + R2H → R1R2+ + H2) between alkane radical cations and alkane molecules. It is concluded that direct ionic dimerisation and condensation are likely to be of little importance in the radiolysis of pure alkanes and of alkane mixtures