Electron paramagnetic resonance studies on labile intermediates in a free-burning methanol-air flame. Effects of water and hydrogen bromide additions

Abstract

Labile intermediates in a premixed methanol-air flame burning freely at atmospheric pressure have been studied by probe sampling and EPR detection. H, O, and OH have been detected at a pressure of 0.45 torr in the EPR cavity. It was found that H and O atoms have their maximum concentrations in the inner flame region within 1 mm from the burner mouth, while the OH concentration slowly increases in the outer flame region to reach a maximum at about 8 mm from the burner mouth. The slow increase in OH concentration is attributed to the reaction H + O/sub 2/ ..-->.. OH + O effectuated by diffusion of O/sub 2/ from the surrounding air into the flame. Addition of H/sub 2/O reduced the O atom concentration and increased the OH radical concentration in the inner flame region. The reaction O + H/sub 2/O ..-->.. 2OH is suggested as an explanation. Addition of HBr gave additional signals from Br and was found to reduce the H, O, and OH concentrations in the flame. It also caused the flame to shrink probably as a result of H atom deficiency in the inner flame region leading to insufficient generation of O and OHmore » in the outer flame region. About 70% of the bromine was found to exist in the atomic form.« less