Penning ionization of NO and O2(1Δg) by argon in the 3P1 state

Electronically excited argon in the 3 P 1 state was generated in a flow system by resonance absorption of the λ=106·7 nm emission line. This photochemical source is particularly convenient for kinetic studies since Ar( 3 P 1 ) alone is produced in the primary exciting step. Energy transfer from excited argon may lead to Penning ionization: This process has been studied for M=NO and M=O 2 ( 1 Δ g ). Relative concentrations of Ar* were estimated from the Penning ion current, and it is shown that Ar* is probably in the initially excited 3 P 1 state and not in the metastable 3 P 2 state. Kinetic studies showed that Penning ionization of NO occurs for about one in every five gas kinetic collisions with Ar( 3 P 1 ). The Penning process can only compete effectively with radiative loss of Ar( 3 P 1 ) as a result of extensive imprisonment of resonance fluorescence. Penning ionization of O 2 ( 1 Δ g ) is shown to proceed at nearly the same rate as ionization of NO. The decrease in Penning ion current on addition of a quenching gas, such as N 2 or O 2 , is used to derive rate constants for the quenching process relative to the rate of quenching by NO. Estimated absolute rate constants are presented in a table.