Thermal decomposition of methyl nitrite: Kinetic modeling of detailed product measurements by gas-liquid chromatography and Fourier transform infrared spectroscopy

The thermal decomposition of CH₃ONO was studied in a static reactor at temperatures in the range 450-520 K. Stable products were analyzed by FTIR and gas-liquid chromatography to yield concentration-time profiles as functions of temperature and pressure. The species monitored included CH₃ONO, CH₂O, CH₃OH, NO, N₂O, and CO. The experimental data were kinetically modeled with the aid of Rice-Ramsperger-Kassel-Marcus (RRKM) calculations for pressure-dependent rate constants. The key reactions of this mechanism are the following: CH₃ONO → CH₃O + NO (1); CH₃ONO → CH₂O + HNO (2); CH₃O + NO → CH₃ONO (3); CH₃O + NO → CH₂O + HNO (4); CH₃O + HNO → CH₃OH + NO (5); HNO + HNO → N₂O + H₂O (7). The results showed that the initiation reaction, (1), is clearly pressure-dependent in the temperature and pressure ranges investigated. The data are consistent with the value k₁ = 10^15.3±0.30 exp((-38 700 ± 400)/RT) s^-1 at 710 Torr of He and with the extrapolated high-pressure rate constant k₁^∞ = 10^16.01±0.30 exp((-39600 ± 400)/RT) s^-1. The rate constant ratio k₄/k₃ for channels 3 and 4 was also found to depend on both temperature and pressure. At 710 Torr, k₃ = 10^12.96±0.30 exp((0 ± 200)/RT) and k₄ = 10^12.92±0.30 exp((-2050 ± 200)/RT), both in units of cm³/(mol s) Kinetic modeling of CH₃OH and N₂O formation over the entire range of temperatures and pressures investigated here yielded k₅ = 10^13.5±0.4 exp((0 ± 400)/RT) and k₇ = 10^8.93±0.30 exp((-3100 ± 300)/RT) cm³/(mol s).