It is well known that the atmosphere of the earth emits a glow throughout the night. The major contribution to this nightglow was first observed in 1901 and was later shown to be due to the transition: O(<SUP>1</SUP>S) → O(^1D) +<i>hv</i>. After many years of controversy, the accepted method for the production of the O(^1S) at a height around 100 km is the Barth mechanism: O(<SUP>3P) + O(<SUP>3P) + M →O <SUP>ast<SUB>2 + M </SUB></SUP>O<SUP>ast<SUB>2 + O(<SUP>3P) →O<SUB>2 + O(<SUP>1S)</SUB></SUP> Where O^ast_2 represents an excited species of oxygen. The precursor can be any of four possible states: O_2(<i>A</i>^3 Σ+_u), O_2(<i>c</i>^1Σ-_u), O_2(<i>A'</i>^3Δu) and O_2(^5πg). All of these states have been proposed as the O(^1S) precursor at one time or another, but none conclusively. For a long time it has been realised that atmospheric measurements of O(^1S), its possible precursors and other relevant species, needs to be taken simultaneously. However up to now this has not been achieved in the laboratory. In the work described here, O(^1S) and the three precursors O_2(<i>A</i>^3Σ+_u), O_2(<i>A'</i>^3Δu) and O_2(<i>c</i>^1Σ-_u) were observed in a laboratory fast flow system. A new method is described whereby upon the addition of a quencher to the system each species can be tested to see if it could be acting as the Barth precursor to O(^1S). Three different quenchers were added in turn; CO_2, SF_6 and O_2. The results gained lead to the conclusion that O_2(<i>c</i>^1Σ-_u), O_2(<i>A'</i>^3Δu) and O_2(<i>A</i>^3Σ+_u)(vleq4) cannot be acting as a O(^1S) precursor, and that O_2(<i>A</i>^3Σ+_u)(vgeq5) is able to do so. The absolute concentrations of O_2(A^3Σ+_u), O(^1S) and O(^3P) were measured and the results compared with the values of these quantities found at a height of 97 km in the earths atmosphere. This comparison shows that O_2(<i>A</i>^3Σ+_u)(vgeq5) can account for all the O(^1S) production at that height at night. The thesis concludes with a discussion of the application of the same method to the determination of the precursors for some of the excited species of O_2.