Formaldehyde photolysis rate

CO -HCHO-air 2 NOx offgasing. Insensitive to radical source parameters but O3 formation is very sensitive to NO offgasing rates. Also can be used to obtain formaldehyde photolysis rates... 

Figures 4.26, 4.27, and 4.28 show typical UV absorption spectra for some simple aldehydes and ketones (Rogers, 1990 Martinez et al., 1992 see also Cronin and Zhu, 1998, for n-pentanal). Formaldehyde stands out from the higher aldehydes and ketones in that it has a highly structured spectrum and furthermore, the absorption extends out to longer wavelengths. The latter difference is particularly important because the solar intensity increases rapidly with wavelength here (Chapter 3.C.1) and hence the photolysis rate constant for HCHO and the rate of production of free radicals...

Formaldehyde has been shown to influence photolysis rates for some compounds. In our experiments formaldehyde at a concentration of 0.4Z did not show absorption above 295 nm and did not affect the photolysis rates of chlorophenols in distilled water (data not presented). ... 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Here the rate constants k refer to the rates of the numbered reactions above the value ho2/ro2 an average for different R02 entities. The A term accounts for HOjj production via ozone photolysis R1-R3, the Bj term accounts approximately for the source from aldehyde photolysis (R12 plus higher aldehydes), and the B2 term is a composite source from formaldehyde (RIO) and dicarbonyls (Cj) less the HOjj sink from PAN formation (R22) B2=Ci-C2). Values for Bj,... 

Photolytic. Atkinson (1985) reported a rate constant of 2.59 x 10 " cmVmolecule-sec at 298 K. Based on an atmospheric OH concentration of 1.0 x 10 molecule/cm , the reported half-life of allyl alcohol is 0.35 d. The reaction of allyl alcohol results in the OH addition to the C=C bond (Grosjean, 1997). In a similar study, Orlando et al. (2001) studied the reaction of allyl alcohol with OH radicals at 298 K. Photolysis was conducted using a xenon-arc lamp within the range of 240-400 nm in synthetic air at 700 mmHg. A rate constant of 4.5 x 10 " cm /molecule-sec was reported. Products identified were formaldehyde, glycolaldehyde, and acrolein. 

Irradiation of gaseous formaldehyde containing an excess of nitrogen dioxide over chlorine yielded ozone, carbon monoxide, nitrogen pentoxide, nitryl chloride, nitric and hydrochloric acids. Peroxynitric acid was the major photolysis product when chlorine concentration exceeded the nitrogen dioxide concentration (Hanst and Gay, 1977). Formaldehyde also reacts with NO3 in the atmosphere at a rate of 3.2 x 10 cmVmolecule-sec (Atkinson and Lloyd, 1984). 

Tuazon et al. (1984a) investigated the atmospheric reactions of TV-nitrosodimethylamine and dimethylnitramine in an environmental chamber utilizing in situ long-path Fourier transform infared spectroscopy. They irradiated an ozone-rich atmosphere containing A-nitrosodimethyl-amine. Photolysis products identified include dimethylnitramine, nitromethane, formaldehyde, carbon monoxide, nitrogen dioxide, nitrogen pentoxide, and nitric acid. The rate constants for the reaction of fV-nitrosodimethylamine with OH radicals and ozone relative to methyl ether were 3.0 X 10 and <1 x 10 ° cmVmolecule-sec, respectively. The estimated atmospheric half-life of A-nitrosodimethylamine in the troposphere is approximately 5 min. 

Because this value has been found independently of a choice of detailed kinetic processes, the mechanism postulated by Calvert and Steacie for the photolysis of formaldehyde requires modification. If, for example, a reaction such as HCO - - CH20 —> H2 + CO + HCO is operative (58) then the activation energy measured for the rate of hydrogen production can no longer be simply associated with the activation energy of the reaction... 

A flow apparatus for detroying 98% of the w-dissolved RDX at flow rates of 2500fi/min is described in Ref 114. The photolysis products include nitrogen gas, nitrous oxide gas. nitrate and nitrite ions, formaldehyde and ammonia. One intermediate product has been identified as l-nitroso-3,5-dimtro-l,3,5-triazacyclohexane. The primary photochemical steps involved in the photolysis are postulated... 

Limited available data suggest that NDMA would be subject to slow photolysis in natural waters exposed to sunlight (Polo and Chow 1976 Callahan et al. 1979). In unlit waters, it appears that NDMA would be rather persistent, eventually degrading as the result of microbial transformation (Kaplan and Kaplan 1985, Kobayashi and Tchan 1978, Tate and Alexander 1975). There is evidence which suggests that formaldehyde and methylamine may form as biodegradation products of NDMA (Kaplan and Kaplan 1985). Insufficient data are available to predict the rate at which NDMA would degrade in water. NDMA is not expected to chemically react under the conditions found in natural waters (Callahan et al. 1979, O.liver et al. 1979). ... 

Recently, Houston and Moore (486) have measured the CO production rate following the pulsed laser photolysis of HjCO and DjCO at 3371 A. They found that at the low pressure limit, the CO rate of production is more than 100 times slower than the fluorescence decay rate. They suggest that CO is not produced from the initially formed fluorescing state S, by light absorption but rather from an intermediate state I. The intermediate state I, cither the or the vibrationally excited ground state, is formed from S, either by collisions or by a spontaneous decay process. The I state dissociates into Hj + CO to a small extent by a slow spontaneous process (>4 /jscc) but to a large extent by collisions with each other or with NO and O2 molecules. The quantum yield of CO production at 3371 A is independent of formaldehyde pressure in the range 0.1 to 10 torr. 

The cleavage of the Co—C bond in organocobalt compounds may occur by the reverse of the three pathways shown in equations (29)-(31). Bond homolysis has been particularly intensively studied, and may occur by photolysis or by thermolysis. Photolysis of the Co—C bond in methylcobalamin is accelerated by the presence of dioxygen, to give B,2a and formaldehyde. The slower rate of the anaerobic photolysis is suggested to result from recombination of Bjjr and methyl radicals. The photolysis of adenosylcobalamin gives 5 -deoxy-5, 8-cycloadenosine and adenosine-5 -carboxaldehyde in the presence of Oj, and the cyclized product only in the absence Of02. 

The rate of recombination of methyl radicals and cobaloxime(II) (i.e. the reverse of Eqn. 45) has been measured by flash photolysis and found to be very high k- ca. 5-8 X 10 /M/sec at 25°C) [82,83]. This presumably explains both the slow rate of photolytic decomposition under strictly anaerobic conditions as well as the marked acceleration of the photolytic decomposition rate in the presence of air due to trapping of the radicals by oxygen. In the latter case the final products are cobalt(III) (i.e. aquocobalamin from methylcobalamin) and formaldehyde, with traces of methanol, methane and formic acid. 

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