Influence of SO2 on chemiluminescence and atom recombination in hydrogen flames

Abstract

The nature of the reactions involving SO₂ which lead to chemiluminescence of certain metal resonance lines in hydrogen flames has been studied by flame photometry. As little as 0.1 % of SO₂ added to a flame containing a small amount of sodium (∼10^–4%) produces a marked increase in the chemiluminescence of the sodium D-lines arising from the region of the flame near the reaction zone. This is attributed to the reaction H+SO₂+Na→HSO₂+Na^*. A similar effect is found for several lines of longer wavelength, but for lines of shorter wavelength, SO₂ decreases chemiluminescence to an extent which increases as the excitation energy involved increases. It is suggested that insufficient energy is released in forming the H—SO₂ bond to excite these latter lines but that in some cases the deficit may be made up by translational energy. The greater rate of decay of chemiluminescence when SO₂ is present as well as measurements of the hydrogen atom concentration in flames containing SO₂ lead to the conclusion that SO₂ catalyzes the recombination of H and OH through the sequence H+SO₂+M→HSO₂+M (7) H+HSO₂→H₂+SO₂(8) OH+HSO₂→H₂O+SO₂(9) Values of the rate constant for reaction (7) have been determined from measurements of the rate of decay of chemiluminescence of the sodium D-lines.