NO formation in a pulsed spark discharge in N2/O2/Ar mixture at atmospheric pressure

Nitrogen monoxide (NO) formation in a pulsed spark discharge is studied in N2/O2/Ar mixture at atmospheric pressure. For monitoring NO formation, vibrationally excited NO(X,ν=3) is measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The LIF with a KrF laser has an advantage that it can also monitor vibrationally excited oxygen O2(X,ν=6) along with NO(X,3). The generation of the O2(X,6) is closely related with the production of O radical or excited oxygen O2* that is generally responsible for NO formation. Therefore, LIF can observe NO formation associated with O and O2* production. LIF analysis shows a similarity between NO(X,3) and O2(X,6) formation when O2 content changes. NO(X,3) and O2(X,6) are not formed at O2 content less than 9%, whereas both molecules increase linearly with O2 concentration when the O2 content exceeds 9%. The similarity between NO(X,3) and O2(X,6) formation suggests that NO is mainly formed by reaction with O or O2*. With the result, the possible NO production processes are discussed. It is concluded that NO is mainly produced by reactions N2*+O or N2*+O2*, where N2* represents an excited nitrogen molecule. (author)