Two-photon absorption laser induced fluorescence (TALIF) detection of atomic iodine in low-temperature plasmas and a revision of the energy levels of I I

International audienceAbstract In order to perfect the use of iodine, instead of xenon, in plasma thrusters, an experiment has been set up to investigate the feasibility of two-photon absorption laser induced fluorescence (TALIF) diagnostics in iodine plasmas. Levels ( 3 P 2 ) 6 p 2 [ 1 ] 3 / 2 o and ( 3 P 2 ) 6 p 2 [ 3 ] 7 / 2 o of atomic iodine were found qualified for that purpose, with a radiative lifetime of the former found equal to 35.5 ( 9 ) n s , which appears consistent with the 32.5 ( 1.2 ) n s predicted by the most recent calculations. Doppler-free two-photon spectroscopy has confirmed that the relative intensities of the hyperfine components follow well-known general formulas, which makes it possible to disentangle the hyperfine structure of 127 I from Doppler broadening. Accurate temperature measurements are shown to be possible, even though the relatively heavy mass of the iodine atom does not make it the most favorable gauge for measurements based on Doppler effect. Using an injection seeded pulsed laser as the primary laser source, the frequency-tripling of which has provided the ca 300 nm radiation used for excitation, absolute energy measurements of the two-photon excited levels revealed that all upper energy levels of I I have to be revised down, by − 0.169 ( 11 ) c m − 1 , which pulls every energy level off its presently tabulated value by more than thirty times the currently admitted uncertainty bar