Absorption cross-sections and absolute concentration of singlet methylene in methane/air flames

Absorption spectra of methylene in the singlet electronic state were measured by intracavity laser absorption spectroscopy in low pressure methane/air flames. Spectra were measured in the region of the (0, 14, 0)–(0, 0, 0) transition (590–593 nm), including the lines with available Einstein coefficients. Comparing the line intensities, the absorption Einstein coefficients and cross-sections for lines of both the (0, 14, 0)–(0, 0, 0) and (0, 13, 0)–(0, 0, 0) transitions were obtained. The absolute concentration profiles of 1CH2 were obtained using the measured Einstein coefficients. These profiles are compared with model calculations and found to be in reasonable agreement. The population of the vibrationally excited (0, 1, 0) level was also determined and found to be slightly higher than the equilibrium value.