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8373144 
Journal Article 
Methylene reaction rates. Quantum yields in the diazomethane-propane photolysis system: Effects of photolysis time, reactant ratios, and added gases 
Bell, JA 
1971 
1 
Journal of Physical Chemistry
ISSN: 0022-3654 
75 
10 
1537-1549 
English 
Quantum yields have been measured for the production of the isomeric butanes in the photolysis of diazomethane-propane mixtures as functions of the C3H8/CH2N2 ratio, total pressure, photolysis time, and added competitor gases, CH4, N2, O2, Ar, and Xe. At C3H8/CH2N2 ratios above about 50, φ(C4H10) = 0.76; at lower ratios φ(C4H10) decreases. Added gases decrease φ(C4H10) by reacting with 1CH2 and/or causing inter-system crossing to 3CH2. The results are all consistent with the following set of reactions and rate constants (cm3 molecule-1 sec-1): CH2N2 + hν (405 nm) → 1CH2 + N2, φ1 = 1.0 ± 0.4 (1); 1H, + C3H8 → C4H10, (6.3 ± 1.7) × 10-12 (2); 1CH2 + C3H8 → 3CH2 + C3H8, (2.4 ± 1.0) × 10-12 (3); 1CH2 + CH2N2 → C2H4 + N2, (31 ± 10) × 10-12 (4); 1CH2 + CH4 → C2H6*, (1.9 ± 0.5) × 10-12 (ref 4); 1CH2 + CH4 → 3CH2 + CH4, (1.6 ± 0.5) × 10-12 (ref 4); 1CH2 + N2 → 3CH2 + N2, (0.5 ± 0.5) × 10-12; 1CH2 + O2 → 3CH2 + O2 (or other products), (4.0 ± 1.0) × 10-12; 1CH2 + Ar → 3CH2 + Ar, (0.8 ± 0.3) × 10-12; 1CH2 + Xe → 3CH2 + ×e, (1.8 ± 0.6) × 10-12. The results imply that the yield of 3CH2 in CH2N2-C3H8 systems is due to reaction 3. Analysis of the isomeric hexane yields gives the ratio of the reaction rates for 8CH2 + C3H8 → CH3 + C3H7 (k5) and 3CH2 + CH2N2 → C2H4 + N2 (k6); k5/k6 = 400 ± 100, so 3CH2 is efficiently scavenged by CH2N2. Two reaction pathways are responsible for the isomeric pentane products: secondary 1CH2 + C4H10 reactions and, probably, C2H5-forming reactions followed by C2H5 + C3H7. Below 100 Torr total pressure the dissociation of C4H10*, formed initially in reaction 2, adds significantly to the yields of the pentanes and hexanes, products associated with the radical reactions following reaction 5. Comparison of these resultes with other studies of CH2 reactions indicates that great care must be taken in assessing relative 1CH2 and 3CH2 yields in the photodissociation of their precursors and the contributions of 1CH2 and 3CH2 reactions to overall product yields.