F与CH~3F反应的可见化学发光

利用分子束装置研究了F与CH~3F反应可见光范围(450-900nm)的化学发光.观察到HCF(A~1A"-X2A')的七个振动带和HF^+电子基态振动广频跃迁的四个振动带和它们的强度随反应物流量的变化.求得HF分子的V'=4,5,6能级相对振动布居和V'=3的转动温度.分析表明两种光谱都是第二步反应(F+CH~2F)引起的,这步反应造成了HF高振动能级的统计性粒子分布和转动能级的玻尔兹曼分布.     

Rates of processes initiated by pulsed laser production of F atoms in the presence of HCl,CH4, and CF3H

Time-resolved vibrational chemiluminescence from HF has been recorded following the production of F atoms by the pulsed laser photolysis (λ = 266 nm) of F₂ in the presence of HCl, CH₄, and CF₃H. In the first two cases, experiments have been conducted by observing emission from HF(ν = 3) at four temperatures from 295 to 139 K. Rate constants have been determined over this range of temperature for the reactions of F atoms with HCl and CH₄ and of CH₃ radicals with F₂, and for the relaxation of HF(ν = 3) by HCl and CH₄. The reaction of F atoms with CF₃H is slower than those with HCl and CH₄ and measurements on the emission from HF(ν = 2) have been used to infer rate constants for reaction and relaxation only at 295 K. © 1994 John Wiley & Sons, Inc.     

Infrared chemiluminescence in the reactions of atomic fluorine with ethanol,propanol-(2) and some deuterated analogs

In the reactive systems F+C₂H₅OH, F+C₂D₅OD, F+C₂H₅OD, F+(CH₃)₂CHOH, F+(CD₃)₂CHOH, and F+(CD₃)₂CDOH the infrared emission spectra were recorded from HF and/or DF in the fundamental region. Hydrogen abstraction takes place from CH and OH bonds. Vibrational relaxation was suppressed and rotational relaxation took place only to a minor extent. HF(DF) excitation reaches the thermodynamic limit within error limits in all cases. The vibrational distributions of HF for the systems F+(CD₃)₂CHOH, F+(CD₃)₂CDOH show no populati inversion. The vibrational distribution of HF for all other systems and all the DF vibrational distributions obtained show population inversion. Inform theory was used to describe the results of those reaction channels that could be studied separately because of isotopic substitution. The results are c to the systems F + methanol and deuterated analogs investigated before in our laboratory, and to the F+CH₄, F+CD₄, and F+H₂O₂ reactio     

Energy resonance and inverse population of the product vibrational states for the reaction F + H2(v = 0) → HF(v′) + H,LCAC‐SW theoretical quantum scattering study

LCAC‐SW (linear combination of arrangement channel‐scattering wavefunction) method was used to calculate collinear state‐to‐state reaction probabilities for the reaction F + H₂(v = 0) → HF(v′) + H on the 6SEC potential energy surface. The results show that reaction probabilities P₀₂ and P₀₃ [i. e., v′ = 2,3 for reaction F + H₂ (v = 0) + HF(v′) + H] are primary, the population of product vibrational states is inverse and the reaction probabilities are oscillatory with collision energies, i.e., there is energy resonance in this reaction, which agrees with a new experiment.     

Hydrogen abstraction by fluorine atoms: F + HX and F + DX (X = I,Br, Cl)

Absolute reaction rates for F + HX and F + DX (X = I, Br, Cl) have been obtained by monitoring the rise time of HF (DF) vibrational fluorescence following multiphoton dissociation of SF₆ in mixtures of HX (DX) and argon. The cross sections for reaction are, in units of 10^?16 cm², 4.37, 5.26, and 1.16 for HI, HBr, and HCl, respectively. The isotope effects k_HX/k_DX, are 1.29 ± 0.14, 1.29 ± 0.18, and 1.38 ± 0.29, respectively.     

Vibrational energy disposal in reactions of fluorine atoms with hydrides of groups III,IV and V

The HF infrared chemiluminescence from the reactions of F atoms with B₂H₆, CH₄, CH₃F, CH₂F₂, CH₂Cl₂, CH₃ONO. CH₃NO₂, NH₃ (and ND₃). PH₃ and HNCO has been observed from a 300 K flowing-afterglow reactor. Experiments were done for a range of CH₄ and F atom concentrations to identify conditions which were free of vibrational relaxation and secondary reactions, and these conditions were used to assign initial HF(v) vibrational distributions for each reaction. The emission intensity from each reaction also was compared to that from CH₄ in order to obtain the relative HF formation rate constants at 300 K. Since the absolute rate constant for F + CH₄ is well established, the combination of all of these data provides absolute rate constants for HF(v) formation at 300 K. The ND₃ reaction was studied to obtain information on more vibrational levels in order to better estimate the HF(v = 0) and DF(v = 0) components of the ammonia distributions. With NH₃ and ND₃ there is no significant isotope effect on the energy disposal. Except for NHCO, for which an addition-elimination channel is possible, the HF(v) distributions are inverted and <f_v > = 0.60. Differences between the HF(v) distributions reported here and some other reports in the literature are noted: the present data are discussed as representative of direct H atom abstraction for 300 K Boltzmann conditions. The HCl infrared chemiluminescence from the F + CHCl₂ secondary reaction also was observed; the HCl(v) distribution was v₁: v₂: v₃: v₄: v₅ - 0.47: 0.23: 0.18: 0.08: 0.04.     

A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor

A small tubular reactor having an inner diameter of 1–2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F₂ and H₂ and CH₄, respectively, is investigated to find out the initiation reactions. In the F₂/H₂ reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F₂/CH₄ case the dominant initiation reaction is the homogeneous reaction CH₄ + F₂ → CH₃ + HF + F. The rate constant for the reaction between 300 and 400 K is 10^12.3±0.3 exp[?47 ± 8 kJ/mol/RT] cm³/mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH₃ + F₂ → CH₃ F + F, which is 10^12.3±0.3 exp[?4.6 ±2.1 kJ/mol/RT] cm³/mol sec.     

Relative rate constants for reactions of HFC 152a, 143, 143a, 134a,and HCFC 124 with F or Cl atoms and for CF2CH3, CF2HCH2, and CF3CFH radicals with F2, Cl2, and O2

Relative rate experiments using UV photolysis of F₂ or Cl₂ have been used to determine rate constant ratios for several hydrofluorocarbon (HFC) reactions with Cl or F atoms and for HFC alkyl radicals with molecular halogens. For mixtures with F₂ present, dark reactions are, also, observed which are attributed to thermal dissociation of the F₂ to form F atoms. At 296 K, the rate of reaction (1a) [CF₂HCH₃ + F → CF₂CH₃ + HF] relative to (1b) [CF₂HCH₃ + F → CF₂HCH₂ + HF] is k_1a/k_1b = 0.73 (±0.13) and is independent of T (= 262–348 K). At 296 K, the ratio of reaction (2a) [CF₂HCH₂F + F → products] to that of (k_1a + k_1b) is (k_1a + k_1b)/k_2a = 2.7 (±0.4), and for reaction (2b) [CF₃CH₃ + F → products] (k_1a + k_1b)/k_2b = 22 ± 12. The temperature dependence (263–365 K) of the rate constant of reaction (3) [CF₃CFH₂ + Cl → products] relative to reaction (4) [CF₃CFClH + Cl → products] is k₃/k₄(±10%) = 1.55 exp(?300 K/T). For the alkyl radicals formed from HFC 152a (CF₂HCH₂ and CF₂CH₃) and from HFC 134a (CF₃CFH), rate constants for the reactions with F₂ and Cl₂ were measured relative to their reactions with O₂. The rate constant of reaction (5cl) [CF₂CH₃ + Cl₂ → CF₂ClCH₃ + Cl] relative to (5o) [CF₂CH₃ + O₂ → CF₂(O₂)CH₃] is k_5cl/k_5o(±15%) = 0.3 exp(200 K/T). For reaction (5f) [CF₂CH₃ + F₂ → CF₃CH₃ + F], k_5f/k_5o(±35%) = 0.23. The ratio for reaction (6f) [CF₂HCH₂ + F₂ → CF₂HCH₂F + F] relative to (6o) [CF₂HCH₂ + O₂ → CF₂HCH₂O₂] is k_6f/k_6o(±40%) = 1.23 exp(?730 K/T). The rate constant ratio for reaction (8cl) [CF₃CFH + Cl₂ → CF₃CFClH + Cl] relative to reaction (8o) [CF₃CFH + O₂ → CF₃CFHO₂] is k_8cl/k_8o(±18%) = 0.16 exp(?940 K/T). For reaction (8f) [CF₃CFH + F₂ → CF₃CF₂H + F], k_8f/k_8o(±35%) = 0.6 exp(?860 K/T). © 1993 John Wiley & Sons, Inc.     

Ab initio and RRKM calculations for the reaction channels of O(1D) + CH3CHF2

Ab initio and Rice–Ramsperger–Kassel–Marcus theories are carried out to study the potential energy surface and the energy‐dependent rate constants and branching ratios of the products for O(¹D) + CH₃CHF₂ reaction. Optimized geometries and vibrational frequencies have been obtained by MP2/6‐311G(d,p) method. The main products of the title reaction are CH₃CFO + HF, CH₂CFOH + HF, and CH₃ + CF₂OH at lower collision energy; and CH₃ + CF₂OH, CH₃CF₂ + OH are the main products at higher collision energy. CHF₂ + CH₂OH are the main products in the whole range of collision energy. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

A two‐step reaction scheme leading to singlet carbene species that can be detected under matrix conditions for the reaction of Zr(3F) with either CH3F or CH3CN

The results obtained from CASSCF‐MRMP2 calculations are used to rationalize the singlet complexes detected under matrix‐isolation conditions for the reactions of laser‐ablated Zr(³F) atoms with the CH₃F and CH₃CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(³F) + CH₃F evolves to the radical products ZrF· + ·CH₃. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(¹D) + CH₃F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic‐matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low‐multiplicity channel produces the inserted structures H₃C? Zr? F and H₂C?ZrHF experimentally detected. For the Zr(³F) + CH₃CN reaction, a similar two‐step reaction scheme involving the radical fragments ZrNC· + ·CH₃ explains the presence of the singlet complexes H₃C? Zr? NC and H₂C?Zr(H)NC revealed in the IR‐matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc.     

The dynamics of formation of vibrationally excited HF in reactions of O (21 D2) atoms with partially fluorinated alkanes

The nascent vibrational energy distributions of the HF? formed in the reactions of a series of partially fluorinated alkanes (R_FH; R_F = CH₂F, CHF₂, CF₃, C₂F₅, C₃F₇, and C₇F₁₅) with electronically excited oxygen atoms O(2¹D₂) have been determined by measuring the appearance times of stimulated emissions from various vibration–rotation transitions in a grating-tuned optical cavity. The vibrational energy contents of the HF formed in these reactions were found to be considerably greater than statistically expected. These reactions are believed to occur via vibrationally excited short-lived α;-fluorinated alcohols (R_FOH?), formed by insertion of the O(2¹D₂) atoms into C? H bonds. The observation of nonstatistical energy partitioning in the above reactions is in clear contrast to the result obtained from the O(2¹D₂) + CF₃CH₃ reaction that produces the β-fluorinated alcohol CF₃CH₂OH, from which the HF product carries a near statistical vibrational energy distribution. A mechanism for HF? formation in these very exothermic reactions is presented.     

Ab initio molecular orbital study on the gas phase SN2 reaction F + CH3Cl → CH3F + Cl

Ab-initio molecular orbital (MO) and direct ab initio dynamics calculations have been applied to the gas phase S_N2 reaction F⁻ + CH₃Cl → CH₃F + Cl⁻. Several basis sets were examined in order to select the most convenient and best fitted basis set to that of high-quality calculations. The Hartree–Fock (HF) 3−21+G(d) calculation reasonably represents a potential energy surface calculated at the MP2/6−311++G(2df,2pd) level. A direct ab initio dynamics calculation at the HF/3−21+G(d) level was carried out for the S_N2 reaction. A full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculation. Total energies and gradients were calculated at each time step. Two initial configurations at time zero were examined in the direct dynamics calculations: one is a near collinear collision, and the other is a side-attack collision. It was found that in the near collinear collision almost all total available energy is partitioned into two modes: the relative translational mode between the products (40%) and the C − F stretching mode (60%). The other internal modes of CH₃F were still in the ground state. The lifetimes of the early- and late-complexes F⁻ … CH₃Cl and FCH₃ … Cl⁻ are significantly short enough to dissociate directly to the products. On the other hand, in the side-attack collision, the relative translation energy was about 20% of total available energy.     

Isomerisation of CF2ClCH2Cl and CFCl2CH2F by Interchange of Cl and F Atoms with Analysis of the Unimolecular Reactions of Both Molecules

The recombination of CF₂Cl with CH₂Cl and CFCl₂ with CH₂F were employed to generate CF₂ClCH₂Cl* and CFCl₂CH₂F* molecules with 381 and 368 kJ mol^?1, respectively, of vibrational energy in a room‐temperature bath gas. The unimolecular reactions of these molecules, which include HCl elimination, HF elimination, and isomerisation by interchange of chlorine and fluorine atoms, were characterized. The three rate constants for CFCl₂CH₂F were 2.9×10⁷, 0.87×10⁷ and 0.04×10⁷ s^?1 for HCl elimination, isomerisation and HF elimination, respectively. The isomerisation reaction must be included to have a complete characterization of the unimolecular kinetics of CFCl₂CH₂F. The rate constants for HCl elimination and HF elimination from CF₂ClCH₂Cl were 14×10⁷and 0.37×10⁷ s^?1, respectively. Isomerisation that has a rate constant less than 0.08×10⁷ s^?1 is not important. These experimental rate constants were matched to calculated statistical rate constants to assign threshold energies, which are 264, 268, and 297 kJ mol^?1, respectively, for isomerisation, HCl elimination, and HF elimination for CFCl₂CH₂F and 314, 251, and 289 kJ mol^?1 in the same order for CF₂ClCH₂Cl. Density functional theory was used to evaluate the models that were needed for the statistical rate constants; the computational method was B3PW91/6‐31G(d′,p′). Threshold energies for the unimolecular reactions of CF₂ClCH₂Cl and CFCl₂CH₂F are compared to those for CF₂ClCH₃ and CFCl₂CH₃ to illustrate the elevation of threshold energies by F‐ or Cl‐atom substitution at the beta carbon atom (identified by C_H). The DFT calculations systematically underestimate the threshold energy for HCl elimination.     

Dynamical Bifurcation in Gas‐Phase XH− + CH3Y SN2 Reactions: The Role of Energy Flow and Redistribution in Avoiding the Minimum Energy Path

The gas‐phase reactions of XH^? (X=O, S) + CH₃Y (Y=F, Cl, Br) span nearly the whole range of S_N2 pathways, and show an intrinsic reaction coordinate (IRC) (minimum energy path) with a deep well owing to the CH₃XH???Y^? (or CH₃S^????HF) hydrogen‐bonded postreaction complex. MP2 quasiclassical‐type direct dynamics starting at the [HX???CH₃???Y]^? transition‐state (TS) structure reveal distinct mechanistic behaviors. Trajectories that yield the separated CH₃XH+Y^? (or CH₃S^?+HF) products directly are non‐IRC, whereas those that sample the CH₃XH???Y^? (or CH₃S^????HF) complex are IRC. The IRCIRC/non‐IRC ratios of 90:10, 40:60, 25:75, 2:98, 0:100, and 0:100 are obtained for (X, Y)=(S, F), (O, F), (S, Cl), (S, Br), (O, Cl), and (O, Br), respectively. The properties of the energy profiles after the TS cannot provide a rationalization of these results. Analysis of the energy flow in dynamics shows that the trajectories cross a dynamical bifurcation, and that the inability to follow the minimum energy path arises from long vibration periods of the X?C???Y bending mode. The partition of the available energy to the products into vibrational, rotational, and translational energies reveals that if the vibrational contribution is more than 80 %, non‐IRC behavior dominates, unless the relative fraction of the rotational and translational components is similar, in which case a richer dynamical mechanism is shown, with an IRC/non‐IRC ratio that correlates to this relative fraction.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.     

Atmospheric chemistry of CH2FOCH2F: Reaction with Cl atoms and atmospheric fate of CH2FOCHFO· radicals

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of CH₂FOCH₂F in 700 Torr of N₂/O₂ at 296 K. Relative rate techniques were used to measure k(Cl + CH₂FOCH₂F) = (4.6 ± 0.7) × 10^?13 and k(Cl + CH₂FOC(O)F) = (2.9 ± 0.8) × 10^?15 (in units of cm³ molecule^?1 s^?1). Three competing fates for alkoxy radical CH₂FOCHFO· formed in the self‐reaction of the corresponding peroxy radicals were identified. In 1 atm of air at 296 K, 48 ± 3% of CH₂FOCHFO· radicals decompose via C? O bond scission, 21 ± 4% react with O₂, and 31 ± 4% undergo hydrogen atom elimination. Chemical activation effects were observed for CH₂FOCHFO· radicals formed in the CH₂FOCHFOO· + NO reaction. Infrared spectra of CH₂FOC(O)F and FC(O)OC(O)F, which are produced during the Cl atom initiated oxidation of CH₂FOCH₂F, are presented. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 139–147, 2002; DOI 10.1002/kin.10038     

Vibrational relaxation of HF(v = 1) by F atoms

The rate of vibrational relaxation of HF(v = 1) by F atoms has been calculated using quasi-classical trajectory techniques. An attempt has been made to account for the effects of multiple potential energy surfaces on the vibrational relaxation efficiency within the electronically adiabatic assumption. Toward this end two potential energy surfaces were investigated. The LEPS equation was used to construct a reactive surface for F + HF′ → FH + F′ having a reaction barrier height of 5.4 kcal/mole, which is in agreement with a bond energy-bond order prediction. A nonreactive interaction potential consisting of atom-atom Morse functions was calibrated to Noble and Kortzeborn's [J. Chem. Phys. 52, 5375 (1970)] LCAO-MO-SCF results for FHF(²II). The results are in qualitative agreement with experiment. However, the nonreactive surface appears to be too repulsive, and consequently, the contribution of collisions on the nonreactive surface to the total vibrational relaxation rate coefficient are overestimated.     

Theoretical Studies on the Reactions of 1,1,2,2,3,3,4‐Heptafluorocyclopentane with Hydroxyl and Hydrogen Free Radicals

1,1,2,2,3,3,4‐Heptafluorocyclopentane (F7A) has considerable potential to be a new halon replacement due to its environmental friendliness and low‐toxicity. However, the reaction processes of F7A with hydroxyl and hydrogen free radicals, which are of great importance for investigating its fire suppression mechanisms, are still unclear. In this paper, ab inito and density functional theory are used to deduce the possible reaction pathways for the reactions of F7A with hydroxyl and hydrogen free radicals at the CCSD/cc‐pVDZ//B3LYP/6‐311++G (d,p) level of theory. Two distinct reaction pathways including ten elementary reaction channels for F7A with hydroxyl free radical, and five distinct reaction pathways including twenty elementary reaction channels for F7A with hydrogen free radical are investigated. The geometries, vibrational frequencies and reaction energy barriers are also determined. Based on the calculated results, the possible reaction mechanisms are proposed and discussed. The most feasible reaction channel for F7A with hydroxyl free radical is that leads to CH(OH)CH₂(CF₂)₃+·F, and the most feasible reaction channel for F7A with hydrogen free radical is that leads to (CF₂)₃CH₂CH·+HF. The study is helpful to further study its fire suppression mechanisms and promote it to be a new generation of halon replacement.     

Rate Coeffcients and Branching Ratio for Multi-Channel Hydrogen Abstractions from CH3OH by F

The hydrogen abstraction reaction F+CH₃OH has two possible reaction pathways: HF+CH₃O and HF+CH₂OH. Despite the absence of intrinsic barriers for both channels, the former has a branching ratio comparable to the latter, which is far from the statistical limit of 0.25 (one out of four available H atoms). Furthermore, the measured branching ratio of the two abstraction channels spans a large range and is not quantitatively reproduced by previous theoretical predictions based on the transition-state theory with the stationary point information calculated at the levels of M?ller-Plesset perturbation theory and G2. This work reports a theoretical investigation on the kinetics and the associated branching ratio of the two competing channels of the title reaction using a quasi-classical trajectory approach on an accurate full-dimensional potential energy surface (PES) fitted by the permutation invariant polynomial-neural network approach to ca. 1.21x10⁵ points calculated at the explicitly correlated (F12a) version of coupled cluster singles doubles and perturbative triples (CCSD(T)) level with the aug-cc-pVDZ basis set. The calculated room temperature rate coeffcient and branching ratio of the HF+CH₃O channel are in good agreement with the available experimental data. Furthermore, our theory predicts that rate coeffcients have a slightly negative temperature dependence, consistent with barrierless nature of the reaction.