Resonance enhanced multiphoton ionization detection of aromatics formation in fuel-rich flames

Polycyclic aromatic hydrocarbons (PAHs) are formed in fuel-rich and sooting hydrocarbon flames. These compounds and smaller aromatic flame constituents, such as benzene, toluene and naphthalene can be detected by flame-sampling molecular beam mass spectrometry (MBMS). They are readily ionized by photoionization with UV light, either in resonant or non-resonant ionization processes. The multiphoton ionization of benzene, toluene, and styrene with MBMS detection was investigated as a function of laser power and wavelength and the quantitative relation between ion signal and mole fractions in the flames was established. These measurements were prerequisites for the measurement of quantitative mole fraction profiles of these species in flames of various fuels. In addition, the measurements provide relative mole fraction profiles of various other aromatic flame species. The results are compared to measurements of aromatics in butadiene, propyne, and allene flames by single-photon ionization with vacuum ultraviolet radiation from a synchrotron source and other literature data.