A mid-infrared diagnostic for benzene using a tunable difference-frequency-generation laser

• DOI: 10.1016/j.proci.2020.06.382
• Publication Date: 2020-09-16T06:24:42Z
• Authors: Mohammad Khaled S...; Mhanna Mhanna; Hanfeng Jin; Dapeng Liu; Khalil Djebbi; Marco Marangoni; Aamir Farooq
• Keywords: Mid infrared spectroscopy; Difference frequency generation; 0103 physical sciences; Shock tube; Benzene; PAH formation; Combustion process; 7. Clean energy; 01 natural sciences; Absorption cross-section

Benzene is a very important molecule in a variety of industrial, environmental, and chemical systems. In combustion, benzene plays an essential role in the formation and growth of polycyclic aromatic hydrocarbons and soot. In this work, a new laser-based diagnostic is presented to make quantitative, interference-free, and sensitive measurements of benzene in the mid-infrared (MIR) region. The diagnostic is based on a widely tunable difference-frequency-generation (DFG) laser system. We developed this laser source to emit in the MIR between 666.54 cm and 790.76 cm as a result of the DFG process between an external-cavity quantum-cascade-laser and a CO gas laser in a nonlinear, orientation-patterned GaAs crystal. Benzene measurements were carried out at the peak (673.94 cm) of the Q-branch of the v vibrational band of benzene. The absorption cross-section of benzene was measured over a range of pressures (4.44 mbar to 1.158 bar) at room temperature. The temperature dependence of the absorption cross-section was studied behind reflected shock waves over 553-1473 K. The diagnostic was demonstrated in a high-temperature reactive experiment of benzene formation from propargyl radicals. The new diagnostic will prove highly beneficial for high-temperature studies of benzene formation and consumption kinetics.