One dimensional temperature measurements by resonantly ionized photoemission thermometry of molecular nitrogen

Abstract

This paper presents an extensive parameter study of a non-intrusive and non-seeded laser diagnostic method for measuring one dimensional (1D) rotational temperature of molecular nitrogen (N2) at 165 - 450 K. Compared to previous efforts using molecular oxygen, here resonantly ionized and photoelectron induced fluorescence of molecular nitrogen for thermometry (N2 RIPT) was demonstrated. The RIPT signal is generated by directly probing various rotational levels within the rovibrational absorption band of N2, corresponding to the 3-photon transition of N2 (X1Σ g +,v=0→b1Π u ,v′=6) near 285 nm, without involving collisional effects of molecular oxygen and nitrogen. The photoionized N2 produces strong first negative band of N2+ (B2Σ u +−X2Σ g +) near 390 nm, 420 nm, and 425 nm. Boltzmann analyses of various discrete fluorescence emission lines yield rotational temperatures of molecular nitrogen. By empirically choosing multiple rotational levels within the absorption band, non-scanning thermometry can be accurately achieved for molecular nitrogen. It is demonstrated that the N2 RIPT technique can measure 1D temperature profile up to ∼5 cm in length within a pure N2 environment. Multiple wavelengths are thoroughly analyzed and listed that are accurate for RIPT for various temperature ranges.