EUCMOS 2008

      Exposing Ar matrices to X-irradiation leads to the creation of electron-hole pairs of which a few always manage to separate and migrate through the matrix, presumably in the form of polarons, until they are scavenged by added guest molecules that have a lower ionization potential (M) or a higher electron affinity than Ar (S), respectively 

           

      The above represents a generally applicable strategy to generate radical cations and (in some cases) radical anions of precursors S or M that can be evaporated without decomposition in Ar which is transparent from ca 180 nm to 100 cm^-1 [1]. The electronic and vibrational spectra that can be recorded from such samples contain much valuable information that allows to draw conclusions about their electronic and molecular structure.
       Among the recent examples from our work that will be discussed are the radical ions of carbon chains R–(C≡C)–R which show very rich and interesting spectra, the radical cations and anions of p-benzoquinone, and some surprising rearrangements of hydrocarbons on oxidation.
      I will also discuss the role of quantum chemisry, on the one had as a spectroscopic modelling tool and on the other hand as a tool to understand the reactivity of radical ions, to elucidate and complement the results from the above experiments.

                    Figure 1: Electronic and vibrational spectra of polyyine radical cations in Ar