Temperature and concentration measurements in acetylene-nitrogen mixtures in the range 300–600 K using dual-broadband rotational CARS

Abstract.

Pure rotational coherent anti-Stokes Raman scattering (CARS) experiments have been performed in acetylene for temperatures ranging from 294 to 582 K, and in mixtures of acetylene and nitrogen in the mole fraction range of 0.06–0.32 for acetylene at room temperature. The experimental spectra are evaluated by a least-square fitting to libraries of theoretically calculated spectra using two different Raman linewidth models, one with and one without dependence on the rotational quantum number J. It is found that a J-dependent model is favourable, both regarding temperature measurements in pure acetylene, and simultaneous acetylene concentration and temperature measurements in different mixtures of acetylene and nitrogen. For the temperature measurements performed in pure acetylene the temperature inaccuracy is generally less than 2% when the J-dependent model for the Raman linewidths is used. It is found that fitting the value of the non-resonant susceptibility significantly improves the quality of the spectral fits and is a requirement for high temperature accuracy with the present model. The evaluated concentrations show a maximum error of 13% on a relative scale. Potential sources of systematical errors both regarding measured temperatures and acetylene concentrations are discussed.