Kinetic investigation of NCO radicals reacting with selected hydrocarbons

Bimolecular rate coefficients for the reactions of isocyanate radicals (NCO ) with ethane (C2H6), allene (C3H4), propene (C3H6), but-1-ene (C4H8) and b ut-1-yne (C4H6) were measured in argon as carrier gas. NCO radicals have be en formed using excimer laser photolysis of chlorine isocyanate (ClNCO) and were detected in their electronic ground state, (X) over tilde (2)Pi, by l aser-induced fluorescence. The NCO + C2H6 reaction was investigated at 20 T orr total pressure in the temperature range 297-899 K. The reaction exhibit s a positive temperature dependence which is well described by the followin g modified Arrhenius equation: k(NCO + C2H6)(T) = (6.2(-3.7)(+3.8)) x 10(-14)(T/298)((3.27+/-0.84)) exp[(- 2.5(-2.3)(+3.4))/RT]cm(3) s(-1) In addition, measurements carried out at 651 K in the pressure range 5-528 Torr showed no pressure dependence, which supports the view that the NCO C2H6 reaction proceeds as a simple H atom abstraction. For the reaction of NCO radicals with allene (C3H4), propene (C3H6), but-1-ene (C4H8) and but-1 -yne (C4H6) bimolecular rate coefficients were determined at room temperatu re and at 20 Torr total pressure. Additionally, the reactions of NCO with C 3H4 and C4H6 were studied at different total pressures. For both reactions, no pressure dependence was observed. The following rate coefficients were obtained at 298 K (in units of 10(-11) cm(3) s(-1)): k(NCO+C3H4) = (1.39 +/ - 0.18), k(NCO+C3H6) = (4.29 +/- 0.20), k(NCO+C4H8) = (6.18 +/- 0.46) and k (NCO+C4H6) = (1.41 +/- 0.14). A correlation between the measured bimolecula r rate coefficients of the NCO reactions with unsaturated hydrocarbons and their ionisation potentials was established.