Measurements of Methyl Radicals and Temperatures by using Coherent Microwave Rayleigh Scattering from Resonance Enhanced Multiphoton Ionization

This thesis includes two main parts: (I) The CH₃[methyl radical] detection in methane/air flames and (II) the rotational temperature measurement of O₂[molecular oxygen] in a variety of environments by using coherent microwave Rayleigh scattering from resonance enhanced multiphoton ionization (Radar REMPI).

In first the part, from Chapter I to Chapter III, the methyl radical detection and quantitative measurements have been conducted in hydrocarbon flame with one-dimensional and two-dimensional spatial-resolved concentration distribution. Due to the proximity of the argon resonance state (4+1 REMPI by 332.5 nm) with the CH₃ state (2+1 REMPI by 333.6 nm), in situ calibration with argon was performed to quantify the absolute concentration of CH₃. The numerical simulations performed using the detailed kinetic mechanism of GRI-3.0 were also provided in the comparison between experimental results and numerical calculations. The details of experimental results and discussions have been reported in Chapter I, II, and III.

In the second part, the O₂ rotational temperature has been measured using Radar REMPI. The Rydberg state C³Π[C3Pi] has been selected as the intermediate state of O₂ in the 2+1 REMPI process, the rotational-resolved spectra from two-photon C³Π←←X³Σ[X3Sigma] transition have been obtained in a variety of conditions from room temperature (294K) to flame temperature (1658 K). The temperature extraction based on the Boltzmann plots has been used in Chapter IV~VI. In Chapter VII, measurements of rotational temperatures of molecular oxygen have been demonstrated based on the empirical analyses of the O₂ spectra without the requirement of highly resolved rotational features using (1) linewidth fitting, (2) linear fitting, and (3) area fitting methods. In the last chapter, the O₂ REMPI spectral model has been built up to accomplish the simulation calculations. The temperature information has been determined based on the comparison between experimental results and REMPI spectral simulations. The O₂ REMPI spectral model has been first reported in the community as a demonstration for the rotational temperature measurement of molecular oxygen with a wide temperature measuring range.