Determination of N2(X) vibrational level populations and rotational temperatures using CARS in a D.C. low pressure discharge

Abstract

For the first time, vibrational level population distributions of a low pressure D.C. flowing discharge were measured up to v=14 using Coherent Anti-Stokes Raman Scattering (CARS). The vibrational populations of the ground state N 2 (X 1 Σ g + ,v) were obtained by recording rotationally resolved CARS spectra of the different vibrational bands. In the discharge region, the vibrational distributions have a non Boltzmann behaviour, as expected. The vibrational parameters were found to lie in the range 4000-5000 K, and rotational temperature to be about 550 K. Similar results were observed in the post-discharge region up to v=10. The vibrational and rotational temperatures were about 3000 and 350 K respectively. The problems experienced while recording CARS spectra in low density media are discussed and comparisons with previously published theoretical models are presented Premieres mesures des populations vibrationnelles de N 2 dans l'etat electronique fondamental jusqu'a v=14 par spectrometrie CARS avec resolution des raies rotationnelles. Observation de distributions vibrationnelles hors equilibre de Boltzmann dans la decharge, avec des parametres vibrationnels compris entre 4000 et 5000 K et une temperature rotationnelle de ∼550 K; resultats similaires dans la post-decharge etudiee jusqu'a v=10