Rare gas matrix studies of absorption and fluorescence of reactive intermediates formed in discharges through acetylene

A simple source of transient species combining a self-igniting discharge with a pulsed supersonic expansion recently developed in our laboratory is applied to the study of discharges through acetylene. It is found to produce particularly efficiently a variety of linear chain compounds. In this article two types of products detected in neon matrices produced with this source are discussed: simple carbon clusters C_n, and polyacetylene radical cations H-(CC)_n-H⁺. The carbon clusters with n ranging from 2 to 9 are observed, and their properties are reviewed and summarized. Well resolved laser excitation and fluorescence spectra of the polyacetylene cations with n = 3 and 4 are analyzed, and compared with available gas phase data, as well as with a recent mass selected matrix study of Maier et al. The differences are explained with the help of site effects and matrix damage.