Absolute intensity calibration of emission spectra: application to the forbidden 346 nm nitrogen line for N((2)P degrees) metastable atoms density measurement in flowing afterglow

作者：Eslami E^*; Sadeghi N

来源：The European Physical Journal - Applied Physics, 2008, 43(1): 93-102.

DOI：10.1051/epjap:2008097

A novel method, based on emission signal from the excitation transfer reaction: Ar*((3)P(2)) + N(2)(X) -> N(2)*(C(3) 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((2)P degrees) 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 degrees- (4)S degrees) line at 346.65 nm, whose transition probability is only 0.005 s(-1). The N((2)P degrees) density variation in the SLA resembles those of N(2)(A(3) 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 x 10(17) m(-3) at the maximum of the SLA. It is proposed that N( 2 P.) density results from a local equilibrium between its production: N(2)(A(3) Sigma(+)(u)) + N((4)S) -> N((2)P) + N(2)(X(1) Sigma(+)(g), nu) and loss: N(2)(X(1) Sigma(+)(g), nu >= 10)+ N((2)P) -> N(2) (A(3) Sigma(+)(u)) + N((4)S) reactions, which strongly couple the atomic and molecular metastable states and hence recycle N(2)(A(3)Sigma(u)) metastable molecules produced in the SLA. The balance equation of N((2)P degrees) density provides a N(2)(X(1) Sigma(g); nu >= 10) density of 6.5 x 10(20) m(-3) at the maximum of the SLA. This corresponds to 1% of the total N(2) molecules in vibrationally excited levels nu >= 10.

• 出版日期2008-7