F+:Highly flammable;
74-86-2Relevant articles and documents
High-Temperature Stabilities of Hydrocarbons
Stein, S. E.,Fahr, A.
, p. 3714 - 3725 (1985)
A chemical thermodynamic analysis of hydrocarbon molecules from 1500 to 3000 K is presented for species C2nH2m, n=1-21, m=1-8.With group additivity as the primary estimation method, the nature and chemical thermodynamic properties of the most stable molecules ( stabilomers ) are found.Concentrations of these molecules are then examined in equilibrium with acetylene and molecular hydrogen after taking into account numbers of isomers.Thermodynamically favored pathways leading to large, condensed polyaromatic species are examined in detail.Two general types of paths are found.At higher H2/C2H2 ratios (>=1), most species on these paths are polycyclic aromatic molecules and, depending on partial pressures of C2H2 and H2, a free energy barrier appears in the range 1400-1800 K which increases sharply with increasing temperature.At lower H2/C2H2 ratios, many smaller species are cyclic, and as this ratio becomes smaller the barrier declines and becomes less sensitive to temperature.A brief dicussion of the connection between these results and the kinetics of carbon polymerization is then presented.
Ion-molecule reactions of ArN2+ with simple aliphatic hydrocarbons at thermal energy
Tsuji, Masaharu,Matsumura, Ken-ichi,Kouno, Hiroyuki,Aizawa, Masato,Nishimura, Yukio
, p. 8687 - 8696 (1994)
The product ion distributions and rate constants are determined for ion-molecule reactions of ArN2+ with C2Hn (n=2,4,6) and C3Hn (n=6,8) by using a thermal ion-beam apparatus.Although charge-transfer channels leading to parent ions and/or fragment ions are found, no displacement reaction leading to ArCmHn+ and N2CmHn+ is detected.A comparison of the product ion distributions with breakdown patterns of the parent ions suggests that fragment ions, formed through cleavage of C-H and/or C-C bonds, are produced via near-resonant ionic states in the 13.1-13.4 eV range.The branching ratios of parent ions for C2H4 (68percent) and C3H6 (20percent) are larger than those for C2H6 (5percent) and C3H8 (5percent).The large branching ratios of the parent ions for the unsaturated hydrocarbons are explained as due to a strong interaction of a vacant orbital of ArN2+ with the highest occupied ?C=C orbital of the unsaturated hydrocarbons which induces nonresonant charge transfer.The total rate constant for C2H2 is 6.8x10-10 cm3 s-1, while those for C2Hn (n = 4,6) and C3Hn (n = 6,8) are in the range (8.5-9.8)x10-10 cm3 s-1.The former and the latter values correspond to 69percent and 77percent-90percent of the calculated values from Langevin or average dipole orientation (ADO) theory.The smaller kobs/kcalc ratio for C2H2 is attributed to the lack of near-resonant ionic states with favorable Franck-Condon factors for ionization.
Reactions of vinyl radicals at high temperatures: Pyrolysis of vinyl bromide iodide and the reaction H + C2D2 → D + C2HD
Rao,Skinner, Gordon B.
, p. 6313 - 6319 (1988)
Five sets of experiments were carried out to determine the rate constant for dissociation of C2H3 at high temperatures. In all cases the measurements involved absorption of H or D Lyman-α radiation in argon-diluted gas mixtures reacting behind shock waves. For pyrolysis of vinyl bromide at 0.5-atm total pressure we found for C2H3 + Ar → C2H2 + H + Ar, k = 7.0 × 1013 exp(-28 kcal/RT) mol-1 cm3 s-1 at 1380-1750 K. For the same reaction initiated from vinyl iodide at 0.5-atm total pressure and 1060-1370 K, we found k = 3.5 × 1014 exp(-33 kcal/RT) mol-1 cm3 s-1. In three sets of experiments in which H atoms reacted with C2D2 to produce D atoms, we obtained values of k∞ for the reaction H + C2H2 → C2H3 of 8 × 1011, 1.2 × 1012, and 3.4 × 1012 mol-1 cm3 s-1 in the temperature range 1200-1900 K, with no clearly visible temperature dependence. All of the experimental values lie 3-10 times lower than those deduced from earlier work at high temperatures or based on ab initio calculations for the vinyl radical.
The Dewar Isomer of 1,2-Dihydro-1,2-azaborinines: Isolation, Fragmentation, and Energy Storage
Edel, Klara,Yang, Xinyu,Ishibashi, Jacob S. A.,Lamm, Ashley N.,Maichle-M?ssmer, C?cilia,Giustra, Zachary X.,Liu, Shih-Yuan,Bettinger, Holger F.
, (2018)
The photochemistry of 1,2-dihydro-1,2-azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yiel
Reactions of ethynyl radicals. Rate constants with CH4, C2H6, and C2D6
Laufer, Allan H.
, p. 3828 - 3831 (1981)
The rate constants for the abstraction of H atoms from CH4, C2H6, and D atoms from C2D6 by C2H (ethynyl) radicals have been determined by using a flash photolysis-kinetic spectroscopic technique. The values obtained, at 297 K, are (1.2 ± 0.2) × 10-12, (6.5 ± 0.4) × 10-12, and (3.1 ± 0.5) × 10-12 cm3 molecule-1 s-1, respectively. The rate constants are independent of added helium over the pressure range 20-700 torr. The kinetic parameters were determined by monitoring the acetylene product spectroscopically using C2H-CF3 as the source of ethynyl radicals.
Thermal Decomposition of Energetic Materials. 25. Shifting of the Dominant Decomposition Site by Backbone Substitution of Alkylammonium Nitrate Salts
Oyumi, Y.,Brill, T. B.
, p. 3657 - 3661 (1987)
Exchanging X = -C(NO2)2F for X = -C(NO2)3 causes the dominating fast thermal decomposition site in NO3 salts to shift from largely that of the C-NO2 bond to largely that of the -H+...NO3- portion.This is consistent with an order of thermal stability of the energetic sites in these salts of -C(NO2)2F>-H+...NO3->-C(NO2)3.These conclusions were drawn from the nature of the IR-active gas products that are evolved in real time upon fast thermolysis (>100 K s-1) and from slow heating of the condensed phase.The O/H ratio of the parent primary ammonium salt appears to be a qualitative indicator of whether NH3(g) will formed under these conditions.Salts with O/H >/= 1 have not been observed to release NH3(g) while those with O/H 1 do.The salt with X=-C(NO2)2F possesses four polymorphs between 297 K and its two melting points.Only two polymorphs are present when X = -C(NO2)3.
Dehydrochlorination of 1,2-dichloroethane over Ba-modified Al2O3 catalysts
Bai, Shuxing,Dai, Qiguang,Chu, Xinxin,Wang, Xingyi
, p. 52564 - 52574 (2016)
Bimodal mesoporous alumina (Al2O3) was prepared using polyethyleneglycol (PEG 20,000) and cetyl trimethyl ammonium bromide as a template. The incorporation of Ba with various loadings was carried out by incipient wetness. Characterization was performed by XRD, N2 sorption isotherms, and pyridine FTIR. Ba can be highly dispersed on Al2O3 covering the strong acid sites of Al2O3. In the catalytic dehydrochlorination of 1,2-dichloroethane (1,2-DCE), the Ba/Al2O3 catalysts present a high activity, of which Al2O3 is most active with 95% conversion at 325 °C, related to the more Lewis acidic Al3+ sites in a tetrahedral environment. 1,2-DCE adsorbs dissociatively on Lewis acid-base pair sites, forming chlorinated ethoxy species, which are supposed to be intermediate species for vinyl chloride (VC) production. At a temperature higher than 400 °C, the dehydrochlorination of VC occurs on the strong acid sites of Al2O3. Ba can promote greatly the selectivity for VC through a decrease in the strong acid sites. A high stable activity for dehydrochlorination and high selectivity for VC can be obtained over Ba/Al2O3 in the presence of oxygen.
Surface kinetics using line of sight techniques: The reaction of chloroform with Cu(111)
Jones, Robert G.,Clifford, Charles A.
, p. 5223 - 5228 (1999)
The adsorption of chloroform (CHCl3) on Cu(111) in the temperature range 100-480 K has been studied using line of sight sticking probability (LOSSP) measurements, line of sight temperature programmed desorption (LOSTPD), low energy electron diffraction (LEED), He I ultra-violet photoelectron spectroscopy (UPS) and work function measurements. Chloroform adsorbs molecularly at 100 K with a sticking probability of 0.98 ± 0.02, the monolayer reacting on heating to 170 K to form chemisorbed chlorine and adsorbed ethyne. The adsorbed ethyne desorbs at just above room temperature with first order kinetics, an activation energy of 77 ± 6 kJ mol-1 and a pre-exponential factor of 10(11±1) s-1. The sticking probability of chloroform on clean Cu(111) at 320 K is 0.23 ± 0.04, which corresponds to activated adsorption at zero coverage with an activation energy of 3.5 ± 0.7 kJ mol-1. The initial sticking probability is found to increase slightly for temperatures above room temperature, and also for temperatures below room temperature, while the sticking probability at finite coverage is greatly increased by the presence of the dissociation product, ethyne, on the surface. These observations are explained in terms of activated adsorption at zero coverage which becomes non-activated at finite coverage due to attractive intermolecular interactions between adsorbed chloroform molecules, and adsorbed chloroform and ethyne molecules.
Competition between photochemistry and energy transfer in ultraviolet-excited diazabenzenes. I. Photofragmentation studies of pyrazine at 248 nm and 266 nm
Sevy, Eric T.,Muyskens, Mark A.,Rubin, Seth M.,Flynn, George W.,Muckerman, James T.
, p. 5829 - 5843 (2000)
The quantum yield for the formation of HCN from the photodissociation of pyrazine excited at 248 nm and 266 nm is determined by IR diode probing of the HCN photoproduct. HCN photoproducts from excited pyrazine are produced via three different dissociation channels, one that is extremely prompt and two others that are late. The total quantum yield from all reaction channels obtained at low quencher gas pressures, φ = 1.3 ± 0.2 for 248 nm and 0.5 ± 0.3 for 266 nm, is in agreement with preliminary studies of this process as well as recent molecular beam studies. To investigate if HCN production is the result of pyrazine multiphoton absorption, this photodissociation process has been further studied by observing the HCN quantum yield as a function of total quencher gas pressure (10 mTorr pyrazine, balance SF6) and as a function of 248 nm laser fluence from 2.8 to 82 mJ/cm2. At the highest SF6 pressures, the HCN quantum yield shows strong positive correlation with laser fluence, indicating that the prompt channel is the result of multiphoton absorption; however, at low pressure, the HCN quantum yield is affected little by changing laser fluence, indicating that the majority of the HCN photoproducts at low pressure are produced from pyrazine which has absorbed only one UV photon. At the lowest pressures sampled, HCN produced from the one-photon late process accounts for more than 95% of all HCN formed (at low laser fluence). At high pressures the single photon late pyrazine dissociation is quenched, and HCN produced at high quencher gas pressures comes only from the multiphoton absorption channel, which can be clearly observed to depend on laser fluence. The HCN quantum yield as a function of laser intensity at high pressure has been fit to a quadratic function that can be used to determine the amount of prompt unquenched HCN produced from multiphoton photodissociation. Additionally, the information theoretic prior functions for energy disposal in the 248 nm photodissociation of pyrazine to form HCN have also been developed. Prior functions for one, two, and three-photon absorption indicate that only HCN with near room temperature translational energy comes from the one-photon process and that all HCN molecules with large amounts of translational energy are produced by multiphoton processes. Finally, analysis of the quenching data within the context of a strong collision model allows an estimate of the rate constant for HCN production from pyrazine for the major late channel, kdls = 1.69 × 105 s-1, for 248 nm excitation, and kdls = 1.33 × 104 s-1 for 266 nm excitation. After 266 nm excitation, pyrazine produced by the major one-photon channel lives for almost an order of magnitude longer than after 248 nm excitation.
Photochemical reactions of cis- and trans-1,2-dichloroethene adsorbed on Pd(111) and Pt(111)
Grassian, Vicki H.,Pimentel, George C.
, p. 4484 - 4491 (1988)
The photochemical behaviors of cis- and trans-1,2-dichloroethene (DCE) adsorbed on Pd ( 111 ) and Pt ( 111 ) surfaces have been studied using electron energy loss spectroscopy ( EELS ) .For multilayer coverage on either metal surface, irradiation of physisorbed DCE at 110 K with broad band irradiation (λ > 200 nm) results in photoisomerization, cistrans.For monolayer coverage on Pt ( 111 ) at 110 K, photolysis of chemisorbed DCE causes loss of the two chlorine atoms to form a single hydrocarbon product, chemisorbed acetylene.Apparently, for λ > 237 nm, the chlorine atoms remain bound to the platinum surface whereas for shorter wavelengths, λ > 200 nm, the chlorine atoms leave the surface.These results are interpretable in terms of singlet excitation of the chemisorbed alkane followed by chlorine elimination on an excited singlet reaction surface.This study indicates that photochemistry of molecules chemisorbed on a metal surface is possible despite the proximity of the conducting surface.It shows that energy relaxation processes connected with this proximity are not prohibitively fast.
