The Formation of Smoke in Flames

Abstract

The setting-up and operation of a quadrupole mass spectrometer for studying the natural ionisation in flames is described, Results are presented for a simple oxygen / hydrogen flame to which two hydrocarbon fuels, ethylene and acetylene were added. The ethylene flame contained forty-two negative flame ion species, whereas the acetylene flame contained thirty-two. These ions are discussed in parallel, due consideration being given to the differences between the flames and to ions formed by the sampling process. In both flames many ions can be attributed to hydrated species of oxygenated parent ions, formed mainly on the sampling nozzle of the apparatus. Some of these hydrated species evidently help to stabilise the parent ion. Ring structures for some of these as a possible explanation of this stabilisation are envisaged. Ions containing C and H only are identified as acetylides and polyacetylides. This formation is favoured in the the acetylene flame because more reactions are thermodynamically possible for the formation of the precursor ions C-, CH-, C2- and C2H-.