Photolysis of formaldehyde-butene mixtures at low pressures. Quantum yield of radical decomposition process in formaldehyde

Abstract

The feasibility of measuring the H-atom quantum yield ( ) in the photolysis of H2CO by the + cis-2-butene and + 1-butene addition reactions below 1 Torr has been studied. This chemical trapping method provides fairly reliable results below ~300 nm. The single vibronic level values of extrapolated to zero-pressure are 0.68 ± 0.10 at 275.4 nm, ~0.6 at 288.2 nm, and 0.68 ± 0.05 at 303.5 nm. These values are in good agreement with the very recent values of Horowitz and Calvert.

Mechanism of the photooxidation of gaseous formaldehyde

“…02CH20H -* (H02CH20) -H02 + CH20 (14) If reaction 14 as well as 7 occurs then in theory the fraction of 02CH20H radicals formed in (7) which ultimately lead to H02CH20H product in (8) should increase with increasing [H02] in the experiments at high [Cl2], Thus the apparent rate of H02 addition to CH20 would be increased with [Cl2] increase as we observe in the plot of Figure 7.…”

“…We may check on the consistency of the present experimental estimates of the rate constants fe7 and fe14 by using thermochemical methods. H02 + CH20 ^02CH20H (7,14) From Benson's additivity rules we can estimate that °-16.8 kcal/mol and AS7°^-32.7 eu (25 °C, 1 atm standard state).21 From these we calculate fe7/fe14 = g-w/RTg^/R " 1-5 x i05 atm-1 = 0.15 ppm-1 (25 °C). This checks well with the ratio of the experimental kinetic estimates of the individual constants: fe7/fe14 = 0.17 ppm-1.…”

“…Taking our experimental estimate for k4 = 0.075 min"1, the literature value for k6 = 5.3 X 103 ppm"1 min"1,19 and a reasonable estimate for ks = 3.0 X 103 ppm"1 min"1, the data give k7/ku = 0.19 ± 0.02 ppm"1. We may also estimate a lower limit for the rate constant for reaction 7 from the value of the ordinate of the plot given in Figure 7 at high [Cl2] and the experimental value for k6: k7 > 10 ppm"1 min"1. We will refine this estimate by using a computer simulation of all of the data after further considerations and additions to the mechanism.…”

Laser-induced photodecomposition of formaldehyde (~A1A2) from its single vibronic levels. Determination of the quantum yield of H-atom by HNO (~A1A") chemiluminescence

“…HNO + 2NO -N2 + HN03 (10) 2HNO -H20 + N20 (11) studies_have shown that the electronically excited HNO*(A1 A") is formed by a three-body process (5a), but we haved added a two-body mechanism (4a) for the sake of completeness. Although the lifetime of HNO* has not been measured directly, it has been estimated to be in the order of <10-7 s in the chemiluminescent system,23 since (010)-( 000) and (001)-(000) emission bands near 700 nm have been observed.13 Since the formation of HNO* by the recombination of HCO and NO is quite endothermic, it is sufficient to consider the lower energy product channel (reaction 9) only.…”

Quantitative detection of HCO behind shock waves: The thermal decomposition of HCO

“…is j ¼ 0.8 at 308 nm as obtained by Moortgat and Warneck. 25 Alternative investigations of j, which resulted in 0.68 < j < 0.7, [28][29][30] were also discussed and reevaluated by Moortgat and Warneck. Other reactions that are important for the formaldehyde system include: 6,[31][32][33][34][35][36][37]…”