Third Body Effects in the Combination of Methyl Radicals

Quantum yields and primary processes in the photolysis of HNCO vapor at 2062 Å

“…At temperatures below 250 "C, the yields of these products were virtually unchanged by the presence of HNCO. Relative yields of the three products were in good accord with previous studies of the azomethane photolysis (7)(8)(9). At 250 "C, with 100 Torr HNCO present, the CH4 yield was marginally enhanced, while that of C2H6 was raised by about 30% (Table I).…”

“…Small amounts of CO, not detected at the lower temperatures, were observed at 250 "C, perhaps arising from subsequent reactions of NCO radicals from reaction [7]. As observed in previous studies of the azomethane photolysis (7)(8)(9), there was considerable loss of methyl radicals to give products other than ethane and methane at the higher temperatures (Table I). There was a marginally greater loss in the presence of HNCO, approximately independent of temperature, suggesting an addition reaction of CH3 wit11 HNCO yielding lligller products which were not detected.…”

“…At 250 "C, with 100 Torr HNCO present, the CH4 yield was marginally enhanced, while that of C2H6 was raised by about 30% (Table I). The latter effect can be attributed to the action of HNCO as a third body for the combination of methyl radicals (8) For personal use only. was more abstraction from HNCO than appears at first sight.…”

“…While the photolysis has not been studied at 2062 A, the trend of observations at longer wavelengths suggest that this assumption is reasonably safe (7)(8)(9). It is supported by the observations that N2 and C2H6 (in equal amounts) were the only products observed, and that the yield of N2 was linearly proportional to the light Relative amounts of light absorbed in both azomethane and HNCO were measured by the platinum photocell, which proved very stable and reliable over a period of months.…”

The photolysis of azomethane in the presence of HN3

“…The suggestion that the N, disappears by reaction [4] or by reaction with CH,N=NCH, in addition to reaction [5] Table 1 shows that the N, recovered was between 23 and 48% less than expected and so the N, must disappear by reaction [4] or by reaction with CH,N=NCH,. At high [HN,] when P -t 1.00 and essentially all CH,'s disappear by reaction [3], we find that there is still a marked deficiency in N,; indeed, the quantity a does not increase consistently with [HN,].…”