Penning ionization of NO and O2(1Δg) by argon in the3P1state

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Abstract
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=O2(1Δ 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 O2(1Δ 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 N2 or O2, 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.

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