The first absolute density measurement of N2(A 3Σ+u;v = 0) metastable molecules in the short-lived nitrogen
afterglow of a 440 Pa microwave discharge is achieved by using a intracavity
laser absorption spectroscopy technique. The results obtained show that this
technique is very well suited for the diagnostics of N2(A 3Σ+u) in the nitrogen afterglow. This is a first important
experimental step with the aim of probing regions where the densities are
expected to be the most significant. The densities measured in the discharge
zone and in the short-lived afterglow maximum emission zone are about
5×1017 and 6×1016 molecule m-3, respectively.
The gas temperature is also deduced both from the Doppler profile of the
spectrally resolved rotational lines and from the rotational distribution in
the N2(A 3Σ+u;v = 0) state. These temperatures are
about 1000 K in the discharge zone and 530 K in the short-lived afterglow
maximum emission zone, respectively. The relatively high density of metastable
molecules in the short-lived afterglow maximum emission zone reveals the
important role played by these species in the short-lived nitrogen afterglow
and can give a new insight into the mechanisms involved in the so-called
nitrogen short-lived afterglow emission. We also conclude that this high
density of N2(A 3Σ+u) in the short-lived afterglow
results from an equilibrium between some local production mechanisms and
destruction by reaction with N atoms.
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