Detection of C2H2 via UV photo-fragmentation, followed by monitoring the C2 d3Πg-a3Πu fluorescence, is explored at atmospheric pressure and at temperatures of 295 K, 600 K, and 800 K, for excitation wavelengths 210 to 240 nm using a broadband laser source (∼3 cm-1 fwhm). At the lower temperature, C2 emissions correlate closely with C2H2 Ã ← X absorption bands, and the excitation spectra suggest a higher-transition probability for the v"4 = 2 and 3 states than for the v"4 = 0 and 1 states. As temperature increases, the excitation spectra exhibit a higher nonresonant background.
Paul C. Miles, Bo Li, Zhongshan Li, and Marcus Aldén, "Atmospheric Pressure Acetylene Detection by UV Photo-Fragmentation and Induced C2 Emission," Appl. Spectrosc. 67, 66-72 (2013)