Kinetic Study of the Thermal Decomposition of Isocyanic Acid in Shock Waves

Article abstract of DOI:10.1246/bcsj.58.3469

Thermal decomposition of isocyanic acid HNCO diluted to less than 2.0 molpercent in argon was studied behind incident shock waves over the temperature range 2100-2500 K.The decomposition course was followed by monitoring the light absorption of HNCO and NH(³Σ^-) at 206 and 336 nm, respectively.It is confirmed that the primary step of the decomposition is a bimolecular process HNCO+Ar->NH(³Σ^-)+CO+Ar, ΔH⁰₀=337 kJ*mol^-1, with the low pressure limit rate constants k=E17.23+/-0.36 exp<-(402+/-17)kJ*mol^-1/RT>cm³*mol^-1*s^-1.The singlet-to-triplet crossing po int is estimated on the basis of the RRKM low-pressure-limit rate constant calculations.The overall decomposition mechanism is suggested and its validity is confirmed by computer simulation of the time-concentration profiles of NH(³Σ^-) at varying temperature.