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The reaction of carbon monoxide and dichlorine over an activated carbon catalyst to produce phosgene is examined using a previously described micro-reactor arrangement. An activation energy of 34.1 kJ mol−1 is determined. The reaction profile at 323 K as a function of time-on-stream establishes steady-state operation to be achieved rapidly, with no deactivation evident within a reaction time of 300 min.. Phosgene production seemingly exhibits 100 % selectivity. However, mass balance measurements indicate a small degree of carbon and chlorine retention by the catalyst that is not directly coupled to the formation of gaseous phosgene. The molecular form of the retained moieties is unknown but, nonetheless, their presence reduces the atom economy of the process and, correspondingly, attenuates total phosgene selectivity. The order of reaction with respect CO, Cl2 and COCl2 is, respectively, 1, 0.5 and 0; leading to the determination of the rate law for phosgene production over this catalyst.

An apparatus is described to investigate the synthesis of phosgene from the reaction of carbon monoxide and dichlorine over an activated carbon catalyst. Infrared spectroscopy and UV–vis absorption spectroscopy are used to identify and quantify reagents and products. The reaction is operated with an excess of CO in order to enable complete chlorine conversion at elevated temperatures. The reaction profile is examined over the temperature range of 300−445 K, with a phosgene selectivity of 100 % observed at all temperatures. An isosbestic point in the UV–vis spectrum is observed at 272 nm, indicating that the dichlorine and the phosgene are in equilibrium. Examination of the phosgene formation rate as a function of space time and catalyst size fraction at 323 K establishes that, under the described conditions, the reaction is operating under chemical control in the absence of mass transfer restrictions.

Acid and redox reaction rates of CH3OH-O2 mixtures on polyoxometalate (POM) clusters, together with isotopic, spectroscopic, and theoretical assessments of catalyst properties and reaction pathways, were used to define rigorous descriptors of reactivity and to probe the compositional effects for oxidative dehydrogenation (ODH) and dehydration reactions. 31P-MAS NMR, transmission electron microscopy and titrations of protons with di-tert-butylpyridine during catalysis showed that POM clusters retained their Keggin structure upon dispersion on SiO2 and after use in CH3OH reactions. The effects of CH3OH and O2 pressures and of D-substitution on ODH rates show that C–H activation in molecularly adsorbed CH3OH is the sole kinetically relevant step and leads to reduced centers as intermediates present at low coverages; their concentrations, measured from UV–vis spectra obtained during catalysis, are consistent with the effects of CH3OH/O2 ratios predicted from the elementary steps proposed. First-order ODH rate...

Acid strength effects on alkane isomerization turnover rates and selectivities are probed using hexene isomers as reactants on bifunctional catalysts containing tungsten Keggin polyoxometalates (POM) with different central atoms and exhibiting well-defined structures amenable to reliable estimates of deprotonation energies (DPE) as rigorous descriptors of acid strength. Titrations of protons with hindered bases during catalysis and mechanistic interpretations of rate data on POM acids in terms of a common sequence of elementary steps give isomerization rate constants that decrease exponentially with increasing DPE. The sensitivity to acid strength is the same for all interconversions among isomeric hexenes because their respective transition states are similar in the amount and localized character of their cationic charges, which determine, in turn, the extent to which the ionic and covalent interactions that determine DPE are recovered upon formation of ion pairs at transition states. The ratios of rate constants for such interconversions, and thus selectivities, are independent of acid strength and their magnitude merely reflects the stability of the gaseous analogs of their respective transition states on all acids.

Phenyl and 4-methylphenyl isocyanide dichlorides are models for byproduct that may be formed in the later stages of certain polyurethane production chains. Photochemical electron paramagnetic resonance (EPR) studies (λ > 310 nm), using the spin trap, N-tert-butyl-α-phenylnitrone, confirm a previously made suggestion that ArN═CCl2 can behave as a chlorine radical source. EPR spectra recorded during and after irradiation and supported by simulations evolve over time and indicate formation of the short-lived spin trap–Cl• adduct and a longer lived benzoyl-N-tert-butylnitroxide radical. Photolysis of C6H5N═CCl2, either alone or mixed with methylene diaryl isocyanate species, in o-C6H4Cl2, a polyurethane process solvent, led to the formation of mixtures containing dichloro- and trichlorobiphenyl isomers.

Dimethyl ether (DME) homologation forms isobutane and triptane (2,2,3-trimethylbutane) with supra-equilibrium selectivities within C 4 and C 7 hydrocarbons on both mesoporous solid acids (SiO 2 –Al 2 O 3 , H 3 PW 12 O 40 /SiO 2 ) and the acid forms of various zeolites (BEA, FAU, MFI) via methylation and hydride transfer steps that favor isobutane and triptane formation because of the relative stabilities of ion-pairs at transition states for chains along the preferred growth path. The stabilities of ion-pair transition states increase as acid sites become stronger and energies for charge separation decrease and as van der Waals interactions within pores become stronger, which respectively lead to higher rates on H 3 PW 12 O 40 /SiO 2 and aluminosilicate zeolites than on amorphous SiO 2 –Al 2 O 3 . Solid acids with different strengths and abilities to solvate ion-pairs by confinement differ in selectivity because strength and solvation influence transition states for the hydride transfer, methylation, and isomerization steps to different extents. Stronger acid sites on H 3 PW 12 O 40 /SiO 2 favor isomerization and hydride transfer over methylation; they lead to higher selectivities to n -butane and non-triptane C 7 isomers than the weaker acid sites on BEA, FAU, and mesoporous SiO 2 –Al 2 O 3 . This preference for hydride transfer and isomerization on stronger acids reflects transition states with more diffuse cationic charge, which interact less effectively with conjugate anions than more localized cations at methylation transition states. The latter recover a larger fraction of the energy required to form the ion-pair, and their stabilities are less sensitive to acid strength than for diffuse cations. Large-pore zeolites (BEA, FAU) form triptane with higher selectivity than SiO 2 –Al 2 O 3 because confinement within large pores preferentially solvates the larger transition states for hydride transfer and methylation, which preserve the four-carbon backbone in triptane, over smaller transition states for alkoxide isomerization steps, which disrupt this backbone and cause growth beyond C 7 chains and subsequent facile β-scission to form isobutane. MFI forms isobutane and triptane with much lower selectivity than mesoporous acids or large-pore zeolites, because smaller pores restrict the formation of bimolecular methylation and hydride transfer transition states required for chain growth and termination steps to a greater extent than those for monomolecular alkoxide isomerization. These data and their mechanistic interpretations show that the selective formation of isobutane and triptane from C 1 precursors like DME is favored on all acids as a result of the relative stability of methylation, hydride transfer, and isomerization transition states, but to a lesser extent when small confining voids and stronger acid sites preferentially stabilize monomolecular isomerization transition states. The observed effects of acid strength and confinement on rates and selectivities reflect the more effective stabilization of all ion-pairs on stronger acids and within solvating environments, but a preference for transition states with more diffuse charge on stronger acids and for ion-pairs with the appropriate solvation within voids of molecular dimensions.

We address here the manner in which acid catalysis senses the strength of solid acids. Acid strengths for Keggin polyoxometalate (POM) clusters and zeolites, chosen because of their accurately known structures, are described rigorously by their deprotonation energies (DPE). Mechanistic interpretations of the measured dynamics of alkane isomerization and alkanol dehydration are used to obtain rate and equilibrium constants and energies for intermediates and transition states and to relate them to acid strength. n-Hexane isomerization rates were limited by isomerization of alkoxide intermediates on bifunctional metal-acid mixtures designed to maintain alkane-alkene equilibrium. Isomerization rate constants were normalized by the number of accessible protons, measured by titration with 2,6-di-tert-butylpyridine during catalysis. Equilibrium constants for alkoxides formed by protonation of n-hexene increased slightly with deprotonation energies (DPE), while isomerization rate constants decreased and activation barriers increased with increasing DPE, as also shown for alkanol dehydration reactions. These trends are consistent with thermochemical analyses of the transition states involved in isomerization and elimination steps. For all reactions, barriers increased by less than the concomitant increase in DPE upon changes in composition, because electrostatic stabilization of ion-pairs at the relevant transition states becomes more effective for weaker acids, as a result of their higher charge density at the anionic conjugate base. Alkoxide isomerization barriers were more sensitive to DPE than for elimination from H-bonded alkanols, the step that limits 2-butanol and 1-butanol dehydration rates; the latter two reactions showed similar DPE sensitivities, despite significant differences in their rates and activation barriers, indicating that slower reactions are not necessarily more sensitive to acid strength, but instead reflect the involvement of more unstable organic cations at their transition states. These compensating effects from electrostatic stabilization depend on how similar the charge density in these organic cations is to that in the proton removed. Cations with more localized charge favor strong electrostatic interactions with anions and form more stable ionic structures than do cations with more diffuse charges. Ion-pairs at elimination transition states contain cations with higher local charge density at the sp(2) carbon than for isomerization transition states; as a result, these ion-pairs recover a larger fraction of the deprotonation energy, and, consequently, their reactions become less sensitive to acid strength. These concepts lead us to conclude that the energetic difficulty of a catalytic reaction, imposed by gas-phase reactant proton affinities in transition state analogues, does not determine its sensitivity to the acid strength of solid catalysts.

The kinetics of the title reactions were investigated at 5−35 Torr total pressure and 265−306 K by UV flash photolysis and time-resolved mass spectrometry. The CH2ClO radical was generated by photo...

The gas-phase kinetics of the CH2ClO radical, formed by flash photolysis of Cl2 in CH3Cl/O2/N2 mixtures, was investigated at 306 K and at total pressures from 5 to 35 Torr by time-resolved mass spectrometry. Reaction of CH2ClO with O2 to form HC(O)Cl and HO2, and unimolecular dissociation to HCl and HCO were both observed. The absolute rate coefficient for reaction of CH2ClO with O2 is (2.8±1.2)×10−13 cm3 molecule−1 s−1. The unimolecular dissociation is well into the fall-off, the rate coefficient increasing from 6×102 s−1 to 4×103 s−1 between 5 and 35 Torr.

The photocatalytic conversion of an aqueous solution of l-tryptophan (Trp) to kynurenine (KN) was investigated under the illumination of different light sources. Results show that Trp converted to KN with a selectivity of 64% under the illumination of a medium pressure (MP) Hg lamp. KN selectivity was increased to >90% when black light (BL) was used a light source. The novel use of BL in the photocatalytic conversion of Trp to KN significantly reduces the energy consumption compared with MP light.

Rate coefficients of the termolecular reaction were determined over the temperature range of 248–324 K and at pressures from 1 to 10 torr by time resolved mass spectrometry. CF2ClO2 radicals were generated by flash photolysis of CF2ClBr in the presence of oxygen. Their rate of decay was measured by following (CF2O2)+ fragment ions formed in the ion source. With 2 to 40 mtorr of NO2 present the dominant removal pathway is addition to form the peroxynitrate. The third order rate coefficients are wholly within the falloff over the experimental pressure range, and have a negative temperature coefficient. Rate constants for the reverse reaction, the unimolecular dissociation of CF2ClO2NO2, D. Koppenkastrop and F. Zabel, Int. J. Chem. Kinet., 23, 1 (1991) were employed to calculate equilibrium constants, from which a 600 torr value of the combination rate coefficient was obtained at each temperature. From the temperature dependence of the equilibrium constants, the average enthalpy of reaction over the experimental temperature range was found to be 106.1 ± 0.3 kJ/mol. Extrapolation of the combination rate constants to lower and higher pressures, and estimates of low and high pressure limiting rate coefficients, k0 and k∞ were done by nonlinear least squares fit of the experimental data, using the empirical Fc equations developed by Troe.

The unimolecular elimination of chlorine atoms from CF{sub 2}ClO and CFCl{sub 2}O radicals has been observed at 238 and 298 K, and at 4-20 Torr total pressure by measurement of the rate of formation of the carbonyl halide product in real time. The fragment ion (CFO){sup +} was found to be specific for the detection of CF{sub 2}O and CFClO and was monitored by time-resolved mass spectrometry in flash photolysis of mixtures of CF{sub 2}ClBr or CFCl{sub 3} with O{sub 2} and NO. These two Cl atom elimination reactions were verified to be very facile, even at low temperatures. The rate constants were estimated by regression analysis of experimentally measured formation curves of CF{sub 2}O and CFClO, and decay curves of CF{sub 2}ClO{sub 2} and CFCl{sub 2}O{sub 2} were determined in the same experiments. The estimated 298 K rate constants are (6.4 {+-} 1.4) x 10{sup 4} s{sup {minus}1} for CF{sub 2}ClO and (1.2 {+-} 0.4) x 10{sup 5} s{sup {minus}1} for CFCl{sub 2}O. 30 refs., 4 figs., 6 tabs.

The kinetics of the reaction of CF{sub 2}ClO{sub 2} radicals with NO{sub 2} at 298 K, investigated by flash photolysis with time-resolved mass spectrometry, are reported. The peroxy radical, CF{sub 2}ClO{sub 2}, was formed in broadband flash photolysis of CF{sub 2}ClBr in the presence of O{sub 2} and detected mass spectrometrically via the fragment ion, CF{sub 2}O{sub 2}{sup +}. With NO{sub 2} present, peroxy radical decay occurs by pseudo-first-order kinetics. The decay rates are also first order in NO{sub 2}. The second-order rate coefficients are pressure dependent over the 1-10 Torr experimental range. The pressure-dependent rate coefficients were fitted by the Troe expression for termolecular reactions. Numerical simulation of the peroxy radical decay rates, using a mechanism consisting of known reactions that also occur in this system, were done to investigate the influence of secondary reactions on the measured rates.

The TEA-CO2 laser induced reaction of trans-l,2-dichloroethylene (TDCE) was investigated at 925 cm-1. The laser radiation was focused to yield beam waist fluences of approximately 125 J cm-2. The major reaction product was cis-1, 2-dichloroethylene (CDCE), with a few per cent of chloroacetylene, and minor amounts of acetylene, dichloroacetylene, chloroethylene and an unidentified C4 compound also being formed. The reaction of pure TDCE was studied as a function of number of laser pulses and total pressure (0.02 to 5 torr). Some experiments were also done with added ethane (20%) and propane (2%). Evidence was obtained that the formation of the cis isomer occurs via two mechanisms, (1) a unimolecular isomerization, and (2) a CI atom chain reaction. The results are consistent with laser induced decomposition of TDCE occurring through the three lowest energy channels: unimolecular structural isomerization (57.4 kcal/mol); molecular HCI elimination (69 kcal/mol); and C-CI bond scission (89 kcal/mol).

The infrared multiple photon trans → cis isomerization of crotonitrile was studied over the pressure range 0.02 torr to 10 torr at fluences of approximately 4J/cm2 using collimated TEA CO2 laser radiation at 942 cm-1. Only minor quantifies of fragmentation products were found at these conditions. At pressures of 0.1 torr or less, the trans form was completely converted to cis form by about 5000 laser pulses. On increasing the pressure a collisional regime was entered in which photostationary states were reached with fewer pulses and having smaller conversions than at low pressure. Both the number of pulses and the conversion decreased monotonically with increasing pressure. The tactic of driving the reaction in the exothermic direction gave evidence that the reaction does not occur solely by thermal isomedzation even in the highly eollisional 10 torr experiments, but that it still has a nonthermal component due to laser induced isomerization.

The kinetics of the decay of hydroxyl radicals in the presence of excess acetylene were studied at pressures in the vicinity of 1 torr and at ambient temperature in a tubular discharge-flow reactor. Hydroxyl radicals were produced by the reaction of atomic hydrogen with nitrogen dioxide, H + NO2 OH + NO. The concentration of hydroxyl was followed by line absorption photometry at 308.939 nm and 308.328 nm. Second-order rate coeffcients were determined in two sets of experiments. The initial concentration ratio [C2H2]0/[OH]0 was in the range of 2.3 to 13.2 in the first set, and 14 to 125 (owing to greater hydroxyl detection sensitivity) in the second set. Values of the second-order rate coefficient obtained were nk5 = (2.9 ± 0.3) × 10−13 cm3/molec-sec in the first set, and nk5 = (2.1 ± 0.6) × 10−13 cm3/molec-sec in the second set, where n is the stoichiometric coefficient of OH. A value of the bimolecular rate constant k5 = (2.0 ± 0.6) × 10−13 cm/molec-sec is consistent with both sets of data, as well as an earlier determination.

The infrared multiple-photon photolysis of trans-2-butene was investigated at five CO/sub 2/ wavelengths from 942 to 1031 cm/sup -1/ and at conversions from a few percent to approximately 95%. The reaction products at 50 m Torr and fluences of approximately 125 J/cm/sup 2/ were cis-2-butene, ethylene, ethane, propylene, propyne, 1,3-butadiene, 1-butene, and 2-butyne. Relative product yields of cis-2-butene and propyne varied significantly with both wavelength and conversion. The results of an investigation of the observed product selectivity are presented.

Flash photolysis of 1,3-dichlorotetrafluoracetone through Suprasil and in Ar diluent gave transient spectra due to the 250-nm band system of CF/sub 2/. With O/sub 2/ present, ClO bands in the 265-292-nm region were observed, and the CF/sub 2/ bands were reduced in intensity. Evidence was found that Cl atoms are the precursor to ClO and that CF/sub 2/ClCOCF/sub 2/ is the precursor to CF/sub 2/. In the absence of O/sub 2/, CF/sub 2/ decayed by the bimolecular association reaction, 2CF/sub 2/ ..-->.. C/sub 2/F/sub 4/. Formation of CF/sub 2/ occurs in 25-50 ..mu..s, while ClO rises to a maximum in about 200 ..mu..s. Both decay over periods of milliseconds. In the presence of O/sub 2/, CF/sub 2/ decay was greatly accelerated, and the ClO decay was faster than could be accounted for by known reactions and reported rate constants. A bimolecular reaction of CF/sub 2/ with ClO was suggested to explain this observation. Evidence that reaction of Cl with CF/sub 2/ClO/sub 2/ is the most important source of ClO was obtained. Two primary photochemical processes, yielding CF/sub 2/Cl radicals and CO, and CF/sub 2/ClCOCF/sub 3/ + Cl, were necessary to adequately explain the results. A detailed mechanism was developed, andmore » numerical simulation employed to fit ClO profiles. The simulation required phi/sub Cl//phi/sub CO/ approx. 0.33. Sensitivity analysis was used to reduce the mechanism to the minimum number of reactions necessary for faithful reproduction of CF/sub 2/ and ClO profiles. 28 references, 8 figures, 2 tables.« less

The variational method of sensitivity analysis is applied to a recent chemical kinetic mechanism for photochemical smog. It is demonstrated that the variational method is capable of readily handling a large mechanism. The analysis can be applied to a single chemical species or to an arbitrarily large group of species contained in an objective function. Examples of the use of different objective functions are given. The variational method provides temporally distributed sensitivity coefficients. Therefore, the results are presented as a time-dependent ranking of reactions in orderof decreasing importance with respect to the objective function species. This ranking permits the time-dependent relative influence of each reaction to be readily determined by inspection. Particular attention is paid to reactions governing daytime O3 formation and nighttime NO3 and HONO formation.

The photolysis of ketene in the presence of cis-2-butene was studied. The effects of pressure and absorbed intensity at 285 and 214 nm were examined, and the effect of small amounts (approximately 5 mole percent) of O/sub 2/ was determined. The hydrocarbon reaction products formed between 250 and 313 nm are consistent with the presence of two reactive electronic states of methylene during photolysis, the ground state, and first excited state. Furthermore, the two states appear to be formed in approximately constant relative proportion over this wavelength region. At 214 nm an increase in the nonstereo-specificity of the methylene addition to the double bond in cis-2-butene can be attributed to the presence of the second excited state. If the second excited state is postulated to be formed from ketene at 214 nm, the results require that it react more rapidly with oxygen than with cis-2-butene, and also indicate that the ground and first excited states of methylene are simultaneously present. (auth)

Room temperature photolysis of up to 100 Torr of 1,1,1-trichloroethane in the presence of iodine at 228.8 nm, and 30 Torr 1,1,1-trichloroethane, also in the presence of iodine, and with added CF 4 was investigated. The main photodecomposition pathways are molecular elimination of HCl and CCl bond scission, with Φ HCl /Φ CCl approximately equal to 3 at low pressure. The yields of CCl 2 CH 2 formed by HCl elimination decrease with increasing pressure, while the products of radical reactions resulting from CCl dissociation are independent of pressure. The results are consistent with Cl atom loss occurring from the σ* state populated by 228.8 nm photoexcitation, while HCl elimination does not occur from either σ* or the ground state, and must proceed through the intermediacy of another excited state, suggested to be a triplet state. Analysis of the pressure dependence of CH 2 CCl 2 yields gave the average energy transferred per gas kinetic collision as 17 ± 5 kcal mol −1 for self-deactivation and 16 ± 6 kcal mol −1 for deactivation by CF 4 .

The quenching of phosphorescence emission from biacetyl, excited at 404.7 nm, has been investigated in the gas phase for several alcohols and iodides. The data gave linear Stern—Volmer plots, from which quenching rate constants for collisions of 3 B u biacetyl were determined. The rate constant values in l/mol s were: methyl alcohol (7.6 × 10 5 ), ethyl alcohol (6.2 × 10 5 ), n-propyl alcohol (7.2 × 10 5 ), methyl iodide (1.0 × 10 6 ), ethyl iodide (1.1 × 10 6 ), n-propyl iodide (6.7 × 10 5 ), and methylene iodide (2.9 × 10 6 ). Using simple hard sphere collision theory, the collisional efficiencies of quenching, per gas kinetic collision, were all in the range 2 to 5 × 10 −6 , except for methylene iodide, which was 1.4 × 10 −5 . The quenching mechanism for the alcohols is most probably H-atom transfer from the alcohol to 3 B u biacetyl. For the iodides, the data cannot be used to distinguish unambiguously between an external heavy atom effect and chemical quenching.

The photolysis of ketene in the presence of methylcyclobutane, cyclohexane, and oxygen was investigated at pressures between 2 and 0.16 Torr at 298/sup 0/K. Chemically activated ethylcyclobutane was formed at energies approximately 50 kcal/mol in excess of the threshold energy for unimolecular decomposition to ethylene and butene-1 by the addition of CH/sub 2/(/sup 1/A/sub 1/) to the methyl group of methylcyclobutane. Cyclohexane, which was present as an internal standard, added CH/sub 2/(/sup 1/A/sub 1/) to yield methylcyclohexane which decomposed by at most 7 percent at the lowest pressures. Experimental evidence was obtained that the collisional deactivation of hot ethylcyclobutane occurs by a multistep process with methylcyclobutane as the principal collision partner. Theoretical calculations, using RRKM theory and a stepladder deactivation model, showed that the data could be fit by deactivation step sizes in the range from 1.5 to 4 kcal/mol. Possibilities for small values of ..delta..E are briefly mentioned.

Photodissociation of 1-iodopropane vapor was studied at 265, 236.5, 222.4 and 214 nm. In all cases highly vibrationally excited n-propyl radicals were formed. Excited n-propyl radical dissociation to methyl radicals and ethylene was observed at all wavelengths shorter than 265 nm; evidence was obtained for a dissociation pathway of lesser significance to hydrogen atoms and propylene. Model calculations indicated that the photodissociation occurs by an impulsive mechanism and that a population inversion of I(2P 1 2 and I(2P 3 2 ) occurs at all wavelengths. Furthermore, the calculations suggest that the inversion is smaller at 214 nm than at wavelengths which are in the 1-iodopropane A band.

The thermal lens technique is applied to infrared multiple photon photochemistry of cyclobutanone at pressures from 1 to 10 Torr, where energy transfer is competitive with the rate of vibrational excitation by absorption of radiation from a pulsed CO/sub 2/ laser beam. Thermal lens signals consisting of rapid (microsecond time scale) oscillations of transmitted HeNe probe laser intensity are attributed to density fluctuations caused by expansion waves that propagate radially toward the center from the outside surface of the laser heated volume, where radially outward propagating shock waves also originate. Gas temperature is estimated from the time delay between the CO/sub 2/ laser pulse and the onset of oscillations. Vibrational temperatures are estimated from the ethylene to cyclopropane product ratio obtained in cyclobutanone photolysis.

The 313 nm photolysis of 1,3-dichlorotetrafluoroacetone in the presence of oxygen was investigated at 298 K. CF2O and CO2 were identified as the reaction products, and a mechanism is proposed to explain their formation. Evidence is obtained for the formation of CO2 by the reaction of CF2ClO radicals with CO.

The behavior of the chlorofluoromethanes CHFCl2 and CHF2Cl in the atmosphere is investigated. The rates of removal by rainout and hydrolysis are estimated to be negligible. Hydrogen abstraction by hydroxyl radicals appears to be an important mechanism for the removal of these compounds. Their photolysis can occur in the stratosphere only, where reactions with singlet oxygen atoms are also of interest. Calculations of reaction and diffusion in the atmosphere, up to 60km, are done, using two different sets of chemical and atmospheric data, as well as two different calculational procedures. The model calculations predict fluorocarbon fluxes at the tropopause ranging from 1 to 3% of the ground level input flux for CHFCl2, and from 4 to 12% of the ground level input flux for CHF2Cl.

The photolysis of ketene in the presence of propylene‐5% oxygen mixtures was investigated at average wavelengths of 3550, 3340, 3130, and 2680 A, and ketene photolysis in the presence of propylene‐n‐pentane‐5% O2 mixtures was investigated at average wavelengths of 3130 and 2680 A. Reaction pressures ranged approximately between 10 and 760 torr. Chemically activated methylcyclopropane, arising from singlet methylene addition to propylene, isomerized to the four butene isomers at each wavelength. The rate of isomerization increased monotonically with decreasing wavelength, demonstrating that the methylcyclopropane average energy increased with increasing photon energy. Of the chemically activated butenes formed either by methylcyclopropane isomerization or by insertion of singlet methylene into the carbon‐hydrogen bonds of propylene, butene‐1 decomposed significantly at the lowest pressures. A multistep process was required to describe the collisional deactivation of chemically activated methylcyclopropane....

The photolysis of ketene or ketene‐d2 in the presence of propane, oxygen, and inert gas was studied at 300°K at each of the four wavelengths 2600, 3130, 3340, and 3500 A. Inert gases used were He, Ar, Xe, N2, and CF4. The inert gases cause the transition of methylene from the first singlet state to the triplet ground state to occur. The observed kinetics of the intersystem crossing process, being first order in methylene and first order in inert gas, are second order. The second‐order rate constants, relative to the rate constant for reaction of singlet methylene with propane, are independent of wavelength, and increase in the order He