Experimental Proof for the Existence of Nonthermal Rotational Distributions of OH (2Σ+) in Flames

Experiments have been carried out to determine whether nonthermal rotational distributions in the 2Σ+ electronic state of OH observed in certain flames are caused by self-absorption. A study of emission (single and double path) and absorption by OH between 3064 A and 3350 A in atmospheric and low-pressure flames has shown that self-absorption is negligible in at least two cases in which nonthermal distributions are found. This leads to the conclusion that anomalous ``temperatures'' of OH measured previously in hydrocarbon flames at low pressure and in highly diluted flames at atmospheric pressure are real.