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Spectroscopic Study of REMPI for Rotational Temperature Measurement in Highly Rarefied Gas Flows

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A measurement technique of thermodynamic variables with high sensitivity is strongly demanded for analyses of highly rarefied gas flows. REMPI Resonantly Enhanced Multiphoton Ionization is a powerful optical tool because of its high sensitivity even in high rarefied gas flows and ability to measure nonequilibrium among internal translational, vibrational, and rotational energy. In this study, to investigate fundamental properties of REMPI signal, the experimental apparatus of 2R2 Nsub 2-REMPI is constructed and the REMPI spectra are measured along the center hue of a free molecular jet. A method of Boltzmann plot using the spectral lines of both 0 and P branches is proposed, determining electronic transition dipole moments in Honl-London factors experimentally from the relative line strength of 0 and P branches. Then an effect of an experimental noise on a rotational temperature measured by the Boltzmann plot becomes smaller because the number of the lines used for the plot increases. By using the factors, simulated spectra agree well with experimental ones, suggesting feasibility of rotational temperature measurement by a spectral fitting.

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  • Fluid Mechanics
  • Optics
  • Nuclear Physics and Elementary Particle Physics

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