ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1-12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O + hν → H + HCO (1): CH2O + hν → H2 + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCO and ΦH2. The ratio ΦCO/ΦH2 was found to be 1.01 ± 0.09(2σ) and (ΦH2 + ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced ΦH2 to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/ΦH2 reached a limiting value of 2.3; with NO addition ΦCO exceeded unity. The addition of small amounts of Me3SiH reduced ΦH2 to 1.02 ± 0.08 and lowered ΦCO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with φ2 = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with φ1 = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)-(5): H + CH2O → H2 + HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2 + 2CO (5). The data suggest k4/k5 ≅ 5.8. Isobutene reduced ΦH2 by the reaction H + iso-C4H8 → C4H9 (20), and the results give k20/k3 ≅ 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k3 and k20.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550100706
