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Despite its key role for the study and modeling of nitrogen chemistry and NOx formation in combustion processes, HCN has only rarely been detected under high-temperature conditions. Here, we demonstrate quantitative detection of HCN behind incident and reflected shock waves using a novel sensitive single-tone mid-infrared frequency modulation (mid-IR-FM) detection scheme. The temperature-dependent pressure broadening of the P(26) line in the fundamental CH stretch vibration band was investigated in the temperature range 670K≤T≤1460K, yielding a pressure broadening coefficient for argon of 2γAr296K=(0.093±0.007)cm−1atm−1 and a temperature exponent of nAr=0.67±0.07. The sensitivity of the detection scheme was characterized by means of an Allan analysis, showing that HCN detection on the ppm mixing ratio level is possible at typical shock wave conditions. In order to demonstrate the capability of mid-IR-FM spectroscopy for future high-temperature reaction kinetic studies, we also report the first successful measurement of a reactive HCN decay profile induced by its reaction with oxygen atoms.

We use offset-frequency-free difference frequency generation comb sources and a Fourier transform spectrometer with comb-mode-width limited resolution to measure and analyze spectra of molecular species of atmospheric relevance: CH3I and CH2Br2 around 3000 cm-1, and 14N 162O around 1280 cm-1.

Hydrogen cyanide (HCN) is the primary cyanide species in combustion processes and plays a key role in the formation of NO x in the combustion of fossil fuels, nitrogencontaining biofuels, and blended hydrocarbon−ammonia mixtures. Robust, sensitive, and time-resolved in situ laser diagnostic methods are needed to gain insight into the combustion chemistry of HCN. Mid-infrared frequency modulation spectroscopy (MIR-FMS) has recently been established as such a quantitative technique for HCN detection behind shock waves. With a minimum detectable fractional absorption of 2 × 10 −4 at a time resolution of 5 μs, an improved spectrometer design enabled the detection of HCN behind shock waves down to the ppm mole fraction level. An Allan noise analysis revealed that a further improvement toward shot-noise limited detection should be possible when fast mid-infrared photodetectors with a higher saturation limit will become available. HCN kinetic profiles in the presence of O( 3 P) atoms from thermal N 2 O decomposition have been measured in the temperature range 1448 K < T < 1954 K. The determined total rate constants for the key HCN oxidation reaction HCN + O, k/(cm 3 mol −1 s −1 ) = 1.88 × 10 14 exp(−64.5 kJ mol −1 /RT)(+28%, −37%), turn out to be largely consistent with previous measurements. These data complete the set of available rate constant studies, by now covering the temperature range 450 K < T < 2500 K and relying on the detection of almost all feasible reactant and product species.