Reaction CH3 + CH3 → C2H6 Studied over the 292-714 K Temperature and 1-100 bar Pressure Ranges.

Reaction of recombination of methyl radicals, CH3 + CH3 → C2H6 (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 292-714 K temperature and 1-100 bar pressure ranges (bath gas He), very close to the high-pressure limit. Methyl radicals were produced by photolysis of acetone at 193.3 nm or in the reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N2O at 193.3 nm, with CH4, and subsequent reaction of OH with CH4. Temporal profiles of CH3 were recorded via absorption at 216.36 and 216.56 nm using a xenon arc lamp and a spectrograph. The absolute intensity of the photolysis light inside the reactor was determined by an accurate in situ actinometry based on the ozone formation in photolysis of N2O/O2/N2 mixtures. The rate constant of reaction 1 in the high-pressure limit has a negative temperature dependence: k1,inf = (5.66 ± 0.43) × 10(-11)(T/298 K)(-0.37) cm(3) molecule(-1) s(-1) (292-714 K).