In attempts to obtain kinetic and mechanistic data required for an assessment of atmospheric fate of alternative halocarbons containing a CF3 group, reactions of the key free radical intermediates CF3OO and CF3O with several atmospheric compounds (i.e., NO, NO2, alkanes and alkenes) have been studied at 297 ± 2 K in 700 torr of air. Experiments employed the long path-FTIR spectroscopic method for product analysis and the visible (400 nm) photolysis of CF3NO → CF3 + NO as a source for the precursor radical CF3. Numerous labile and stable F-containing molecular products have been characterized based on kinetic and spectroscopic data obtained at sufficiently short photolysis time (≤1 min) to minimize heterogeneous decay on the reactor walls. Major new findings have been made for the reactions involving CF3O radicals. The behavior of CF3O radicals has been shown to be markedly different from that of CH3O radicals, i.e., (1) O2-reaction: no evidence for the F-atom transfer reaction CF3O + O2 → CF2 O + FOO; (2) NO-reaction: addition reaction CH3O + NO (+M) → CH3ONO (+M), but F-transfer reaction CF3O + NO → CF2O + FNO; (3) NO2-reaction: addition reaction for both radicals, but F-transfer reaction CF3 + NO2 → CF2O + FNO2 to a minor extent; (4) alkane-reaction: much faster H-abstraction by CF3O, comparable to HO; (5) alkene-reaction: much faster addition reaction of CF3O, comparable to HO. These results are summarized in this paper. 相似文献
A fluorescence excitation spectrum of (CH3)2CHO (isopropoxy radical) is reported following photolysis of isopropyl nitrite at 355 nm. Rate constants for the reaction of isopropoxy with NO, NO2, and O2 have been measured as a function of pressure (1–50 Torr) and temperature (25–110°C) by monitoring isopropoxy radical concentrations using laser-induced fluorescence. We have obtained the following Arrhenius expressions for the reaction of isopropoxy with NO and O2 respectively: (1.22±0.28)×10?11 exp[(+0.62±0.14 kcal)/RT]cm2/s and (1.51±0.70)×10?14 exp[(?0.39±0.28)kcal/RT]cm3/s where the uncertainties represent 2σ. The results with NO2 are more complex, but indicate that reaction with NO2 proceeds more rapidly than with NO contrary to previous reports. The pressure dependence of the thermal decomposition of the isopropoxy radical was studied at 104 and 133°C over a 300 Torr range using nitrogen as a buffer gas. The reaction is in the fall-off region over the entire range. Upper limits for the reaction of isopropoxy with acetaldehyde, isobutane, ethylene, and trimethyl ethylene are reported.We have performed the first LIF study of the isopropoxy radical. Arrhenius parameters were measured for the reaction of i-PrO with O2, NO, NO2, using direct radical measurement techniques. All reactions are in their high-pressure limits at a few Torr of pressure. The rate constant for the reactions of i-PrO with NO and NO2 reactions exhibit a small negative activation energy. Studies of the i-PrO + NO2 reaction produce data which indicate that O(3P) reacts rapidly with i-PrO. Unimolecular decomposition studies of i-PrO indicate that the reaction is in the fall-off region between 1 and 300 Torr of N2 and the high-pressure limit is above 1 atmosphere of N2. 相似文献
The conformational properties of methanesulfonyl peroxynitrate, CH3S(O)2OONO2 (MSPN), and its radical decomposition products CH3S(O)2OO· and CH3S(O)2O· were studied by ab initio and density functional methods. The dihedral angle around the S–O and the O–O single bond are calculated to be ?70.5° and ?97.8° (B3LYP/6‐311++G(3df,3pd)), respectively. The principal unimolecular dissociation pathways for MSPN were studied using complete basis set (CBS) methods. The reaction enthalpies for the channels CH3S(O)2OONO2→ CH3S(O)2OO·+NO2 and CH3S(O)2OONO2→CH3S(O)2O·+NO3 were computed to be 111.0 and 140.9 kJ/mol, respectively. The enthalpies of formation at 298 K for MSPN and CH3S(O)2OO radical were predicted to be ?358.2 and ?281.3 kJ/mol, respectively. 相似文献
The hybrid method B3LYP/6-311G* of density functional theory is used to optimize the geometries of nitroform and some intermediates of its decomposition (CH(NO2)2, CH(NO2)2ONO, CH(NO2), and HC(O)NO) and to locate the transition states of the dissociation and isomerization reactions involving these species. The heat of formation of nitroform and of the intermediates of its decomposition and the Gibbs energies of activation of the reactions examined are calculated using the modern ab initio multilevel procedures G2M(CC5) and G2. The high-pressure limits of the rate constants of these reactions in the temperature range 300–2000 K are calculated using transition state theory or its variational analogue. 相似文献
Product studies were made using the Fourier transform infrared method in the uv (300–400-nm) photolysis of mixtures containing CH3SCH3, C2H5ONO, and NO in ppm concentrations in 700 torr of O2–N2 diluent. Methyl thionitrite, CH3SNO, arising from the reaction CH3S + NO, was detected as an intermediate product. In addition, the yields of the major sulfur-containing products SO2 and CH3SO3H coincided with those of the oxidation of the CH3S radicals generated directly by the photodissociation of CH3SNO. The formation of CH3S in the HO-initiated oxidation of CH3SCH3 in the presence of NO suggests a reaction scheme involving the H-abstraction reaction HO + CH3SCH3 → CH3SCH2 + H2O as the primary step. 相似文献
Thermochemistry and kinetic pathways on the 2-butanone-4-yl (CH3C(=O)CH2CH2•) + O2 reaction system are determined. Standard enthalpies, entropies, and heat capacities are evaluated using the G3MP2B3, G3, G3MP3, CBS-QB3 ab initio methods, and the B3LYP/6-311g(d,p) density functional calculation method. The CH3C(=O)CH2CH2• radical + O2 association reaction forms a chemically activated peroxy radical with 35 kcal mol−1 excess of energy. The chemically activated adduct can undergo RO−O bond dissociation, rearrangement via intramolecular hydrogen transfer reactions to form hydroperoxide-alkyl radicals, or eliminate HO2 and OH. The hydroperoxide-alkyl radical intermediates can undergo further reactions forming ketones, cyclic ethers, OH radicals, ketene, formaldehyde, or oxiranes. A relatively new path showing a low barrier and resulting in reactive product sets involves peroxy radical attack on a carbonyl carbon atom in a cyclic transition state structure. It is shown to be important in ketones when the cyclic transition state has five or more central atoms. 相似文献
The mechanisms of CH2SH with NO2 reaction were investigated on the singlet and triplet potential energy surfaces (PES) at the BMC-CCSD//B3LYP/6-311 + G(d,p) level. The result shows that the title reaction is more favourable on the singlet PES thermodynamically, and it is less competitive on the triplet PES. On the singlet PES, the initial addition of CH2SH with NO2 leads to HSCH2NO2 (IM2) without any transition state, followed by a concerted step involving C–N fission and shift of H atom from S to O giving out CH2S + trans-HONO, which is the major products of the title reaction. With higher barrier height, the minor products are CH2S + HNO2, formed by a similar concerted step from the initial adduct HSCH2ONO (IM1). The direct abstraction route of H atom in SH group abstracted by O atom might be of some importance. It starts from the addition of the reactants to form a weak interaction molecular complex (MC3), subsequently, surmounts a low barrier height leading to another complex (MC2), which gives out CH2S + trans-HONO finally. Other direct hydrogen abstraction channels could be negligible with higher barrier heights and less stable products. 相似文献
The potential energy surface of O(1D) + CH3CH2F reaction has been studied using QCISD(T)/6-311++G(d,p)//MP2/6-311G(d,p) method. The calculations reveal an insertion–elimination reaction mechanism of the title reaction. The insertion process has two possibilities: one is the O(1D) atom inserting into C–F bond of CH3CH2F produces one energy-rich intermediate CH3CH2OF and another is the O(1D) atom inserting into one of the C–H bonds of CH3CH2F produces two energy-rich intermediates, IM1 and IM2. The three intermediates subsequently decompose to various products. The calculations of the branching ratios of various products formed though the three intermediates have been carried out using RRKM theory at the collision energies of 0, 5, 10, 15, 20, 25 and 30 kcal/mol. CH3CH2O is the main decomposition product of CH3CH2OF. HF and CH3 are the main decomposition products for IM1; CH2OH is the main decomposition product for IM2. Since IM1 is more stable and more likely to form than CH3CH2OF and IM2, HF and CH3 are probably the main products of the O(1D) + CH3CH2F reaction. Our computational results can give insight to reaction mechanism and provide probable explanations for future experiments. 相似文献
The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(?2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K. 相似文献
The kinetics of the acetaldehyde pyrolysis have been studied at temperatures from 450° to 525°C, at an acetaldehyde pressure of 176 torr and at 0 to 40 torr of added nitric oxide. The following products were identified and their rates of formation measured: CH4, H2, CO, CO2, C2H4, C2H6, H2O, C3H6, C2H5CHO, CH3COCH3, CH3COOCH?CH2, N2, N2O, HCN, CH3NCO, and C2H5NCO. Acetaldehyde vapor was found to react with nitric oxide slowly in the dark at room temperature, the products being H2O, CH3COOCH3, CO, CO2, N2, NO2, HCN, CH3NO2, and CH3ONO2. The rates of formation of N2 and C2H5NCO depend on how long the CH3CHO-NO mixture is kept at room temperature before pyrolysis; the rates of formation of the other products depend only slightly on the mixing period. The pyrolysis of “clean” CH3CHO–NO mixtures (i.e., the results extrapolated to zero mixing time, which are independent of products formed in the cold reaction) are interpreted as follows: (1) There are two chain carriers, CH3 and CH2CHO, their concentrations being interdependent and influenced by NO in different ways: the CH3 radical is both generated and removed by reactions directly involving NO, whereas CH2CHO is generated only indirectly from CH3 but is also removed by direct reaction with NO. (2) An important mode of initiation by NO is its addition to the carbonyl group with the formation of which is converted into ; this splits off OH with the formation of CH3NCO or CH3 + OCN. (3) Important modes of termination are The steady-state equations derived from the mechanism are shown to give a good fit to the experimental rate versus [NO] curves and, in particular, explain why there is enhancement of rate by NO at higher CH3CHO pressures and, at lower CH3CHO pressures, inhibition at low [NO] followed by enhancement at higher [NO]. The cold reaction is explained in terms of chain-propagating and chain-branching steps resulting from the addition of several NO molecules to CH3CHO and the CH3CO radical. In the “unclean” reaction it is found that the rates of N2 and C2N5NCO formation are increased by CH3NO2, CH3ONO, and CH3ONO2 formed during the cold reaction. A mechanism is proposed, involving the participation of α-nitrosoethyl nitrite, CH3CH(NO)ONO. It is suggested that there are two modes of behavior in pyrolyses in the presence of NO: (1) In the paraffins, ethers, and ketones, the effects are attributed to the addition of NO to a radical with the formation of an oxime-like compound. (2) In the aldehydes and alkenes, where there is a hydrogen atom attached to a double-bonded carbon atom, the behavior is explained in terms of addition of NO to the double bond followed by the formation of an oxime-like species. 相似文献
The thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 → antisymmetric-NO3 + NO. The results on the reaction, NO2 + SO2 → NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low-temperature data and provides a modification of the rate-constant expression that is applicable over a wide temperature range. 相似文献