Article contents
Absolute intensity calibration of emission spectra: application to the forbidden 346 nm nitrogen line for N(2P°) metastable atoms density measurement in flowing afterglow
Published online by Cambridge University Press: 30 May 2008
Abstract
A novel method, based on emission signal from the
excitation transfer reaction: Ar*(3P2) + N2(X) $\to $
N2*(C3$\Pi_{u}$
) + Ar, is proposed for the intensity
calibration of the spectroscopic optical detection system in absolute scale.
It is applied for the measurement of N(2P°) metastable atoms
density in the Short Lived Afterglow (SLA) of a 440 Pa nitrogen discharge
produced by a 433 MHz resonant cavity. This density is deduced from the
absolute intensity of the forbidden N(2P°–4S°) line at
346.65 nm, whose transition probability is only 0.005 s−1. The
N(2P°) density variation in the SLA resembles those of
N2(A3$\Sigma_{u}$
) metastable molecules and electrons or the
emission intensities of first positive (1+), second positive (2+)
and first negative (1−) systems of N2. It first decays after the
discharge zone up to a minimum and hence increases by almost a factor of
thirty to reach a maximum value of 6 × 1017 m−3 at the maximum of
the SLA. It is proposed that N(2P°) density results from a local
equilibrium between its production: N2(A3$\Sigma _{u}^{+}$
) + N(4S) $\to $
N(2P) + N2(X1$\Sigma _{g}^{+}$
, v) and
loss: N2(X1$\Sigma _{g}^{+}$
, v≥ 10)+ N(2P) $\to
$
N2 (A3$\Sigma _{u}^{+}$
) + N(4S) reactions, which
strongly couple the atomic and molecular metastable states and hence recycle
N2(A3$\Sigma _{u}$
) metastable molecules produced in the SLA.
The balance equation of N(2P°) density provides a
N2(X1$\Sigma _{g}$
; v≥ 10) density of 6.5 × 1020
m−3 at the maximum of the SLA. This corresponds to 1% of the total
N2 molecules in vibrationally excited levels v≥ 10.
- Type
- Research Article
- Information
- Copyright
- © EDP Sciences, 2008
References
- 10
- Cited by