共查询到20条相似文献,搜索用时 15 毫秒
1.
Beaver MR Simmons JG Heard GL Setser DW Holmes BE 《The journal of physical chemistry. A》2007,111(34):8445-8455
Vibrationally excited CF(2)ClCHFC(2)H(5)(CF(2)ClCHFC(2)D(5)) molecules were prepared in the gas phase at 300 K with approximately 93 kcal mol(-1) of energy by recombination of CF(2)ClCHF and C(2)H(5) or C(2)D(5) radicals. Three unimolecular reactions were observed. 1,2-ClF interchange converts CF(2)ClCHFC(2)H(5)(CF(2)ClCHFC(2)D(5)) into CF(3)CHClC(2)H(5)(CF(3)CHClC(2)D(5)), and subsequent 2,3-ClH (ClD) elimination gives CF(3)CH=CHCH(3) (CF(3)CH=CDCD(3)). 2,3-FH(FD) elimination gives cis- and trans-CF(2)ClCH=CHCH(3) (CF(2)ClCH=CDCD(3)), and 1,2-ClH elimination gives CF(2)=CFCH(2)CH(3) (CF(2)=CFCD(2)CD(3)). The experimental rate constants for CF(2)ClCHFC(2)H(5) (CF(2)ClCHFC(2)D(5)) were 1.3 x 10(4) (0.63 x 10(4)) s(-1) for 1,2-FCl interchange and 2.1 x 10(4) (0.61 x 10(4)) s(-1) with a trans/cis ratio of 3.7 for 2,3-FH(FD) elimination. The 1,2-ClH process was the least important with a branching fraction of only 0.08 +/- 0.04. The rate constants for 2,3-ClH (ClD) elimination from CF(3)CHClC(2)H(5) (CF(3)CHClC(2)D(5)) were 1.8 x 10(6) (0.49 x 10(6)) s(-1) with a trans/cis ratio of 2.4. Density functional theory was used to compute vibrational frequencies and structures needed to obtain rate constants from RRKM theory. Matching theoretical and experimental rate constants provides estimates of the threshold energies, E0, for the three reaction pathways; 1,2-FCl interchange has the lowest E0. The unimolecular reactions of CF(2)ClCHFC(2)H(5) are compared to those of CF(2)ClCHFCH(3). Both of these systems are compared to CH(3)CHFC(2)H(5) to illustrate the influence of a CF(2)Cl group on the E0 for FH elimination. 相似文献
2.
Papadimitriou VC Papanastasiou DK Stefanopoulos VG Zaras AM Lazarou YG Papagiannakopoulos P 《The journal of physical chemistry. A》2007,111(45):11608-11617
The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF(3)CH(2)CH(2)OH (1), CF(3)CF(2)CH(2)OH (2), CHF(2)CF(2)CH(2)OH (3), and CF(3)CHFCF(2)CH(2)OH (4), were studied in the gas phase over the temperature range of 273-363 K by using very low-pressure reactor mass spectrometry. The absolute rate coefficients were given by the expressions (in cm(3) molecule(-1) s(-1)): k(1) = (4.42 +/- 0.48) x 10(-11) exp(-255 +/- 20/T); k(1)(303) = (1.90 +/- 0.17) x 10(-11), k(2) = (2.23 +/- 0.31) x 10(-11) exp(-1065 +/- 106/ T); k(2)(303) = (6.78 +/- 0.63) x 10(-13), k(3) = (8.51 +/- 0.62) x 10(-12) exp(-681 +/- 72/T); k(3)(303) = (9.00 +/- 0.82) x 10(-13) and k(4) = (6.18 +/- 0.84) x 10(-12) exp(-736 +/- 42/T); k(4)(303) = (5.36 +/- 0.51) x 10(-13). The quoted 2sigma uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis mechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and the end products were the corresponding aldehydes (R(F)-CHO; R(F) = -CH(2)CF(3), -CF(2)CF(3), -CF(2)CHF(2), and -CF(2)CHFCF(3)), providing a strong experimental indication that the primary reactions proceed mainly via the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and ionization potentials for the title compounds were determined by density functional theory calculations, which also suggest that the alpha-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of room-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated C2-C5 ethers and C2-C4 alcohols, is good with an average deviation of a factor of 2, and is given by the expression log(k) (in cm(3) molecule(-1) s(-1)) = (5.8 +/- 1.4) - (1.56 +/- 0.13) x (ionization potential (in eV)). 相似文献
3.
K. Tokuhashi A. Takahashi M. Kaise S. Kondo A. Sekiya S. Yamashita H. Ito 《国际化学动力学杂志》1999,31(12):846-853
The rate constants for the reactions of OH radicals with CH3OCF2CF3, CH3OCF2CF2CF3, and CH3OCF(CF3)2 have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis, laser photolysis, and discharge flow methods combined respectively with the laser induced fluorescence technique. The influence of impurities in the samples was investigated by using gas‐chromatography. The following Arrhenius expressions were determined: k(CH3OCF2CF3) = (1.90) × 10−12 exp[−(1510 ± 120)/T], k(CH3OCF2CF2CF3) = (2.06) × 10−12 exp[−(1540 ± 80)/T], and k(CH3OCF(CF3)2) = (1.94) × 10−12 exp[−(1450 ± 70)/T] cm3 molecule−1 s−1. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 846–853, 1999 相似文献
4.
Rate constants for the gas‐phase reactions of CH3OCH2CF3 (k1), CH3OCH3 (k2), CH3OCH2CH3 (k3), and CH3CH2OCH2CH3 (k4) with NO3 radicals were determined by means of a relative rate method at 298 K. NO3 radicals were prepared by thermal decomposition of N2O5 in a 700–750 Torr N2O5/NO2/NO3/air gas mixture in a 1‐m3 temperature‐controlled chamber. The measured rate constants at 298 K were k1 = (5.3 ± 0.9) × 10?18, k2 = (1.07 ± 0.10) × 10?16, k3 = (7.81 ± 0.36) × 10?16, and k4 = (2.80 ± 0.10) × 10?15 cm3 molecule?1 s?1. Potential energy surfaces for the NO3 radical reactions were computationally explored, and the rate constants of k1–k5 were calculated according to the transition state theory. The calculated values of rate constants k1–k4 were in reasonable agreement with the experimentally determined values. The calculated value of k5 was compared with the estimate (k5 < 5.3 × 10?21 cm3 molecule?1 s?1) derived from the correlation between the rate constants for reactions with NO3 radicals (k1–k4) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH3OCH2CF3 and CHF2CF2OCH2CF3 to be 240 and >2.4 × 105 years, respectively, with respect to reaction with NO3 radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009 相似文献
5.
Disproportionation/combination rate constant ratios, kd/kc, for the reactive collision between CF3CH2CHX + CF3 radicals and between CF3CH2CHX + CF3CH2CHX radicals have been measured for X = CF3. The kd/kc = 0.066 ± 0.013 when H is transferred to the CF3 radical and 0.125 ± 0.025 for H transfer to the CF3CH2CHCF3 radical. Comparison of these results with previous work shows that X = CF3 increases the kc/kc' s relative to X = Cl or H. The effect of the CF3 substituent on the disproportionation rate is discussed. © 1996 John Wiley & Sons, Inc. 相似文献
6.
Timothy J. Wallington Michael D. Hurley Jichun Shi M. Matti Maricq Jens Sehested Ole J. Nielsen Thomas Ellermann 《国际化学动力学杂志》1993,25(8):651-665
A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm3 molecule?1 s?1: CH3F, (3.7 ± 0.8) × 10?11, CH3Cl, (3.3 ± 0.7) × 10?11; CH3Br, (3.0 ± 0.7) × 10?11; CF2H2, (4.3 ± 0.9) × 10?12; CO, (5.5 ± 1.0) × 10?13 (in 700 torr total pressure of N2 diluent); CF3H, (1.4 ± 0.4) × 10?13; CF3CCl2H (HCFC-123), (1.2 ± 0.4) × 10?12; CF3CFH2 (HFC-134a), (1.3 ± 0.3) × 10?12, CHF2CHF2 (HFC-134), (1.0 ± 0.3) × 10?12; CF2ClCH3 (HCFC-42b), (3.9 ± 0.9) × 10?12, CF2HCH3 (HFC-152a), (1.7 ± 0.4) × 10?11; and CF3CF2H (HFC-125), (3.5 ± 0.8) × 10?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc. 相似文献
7.
Disproportionation/combination rate constant ratios, kd /kc, have been measured for the collision between CF3CH2CH2 and CF3 radicals to be 0.022 ± 0.002 and for CF3CH2CH2 and CF3CH2CH2 radicals to be 0.100 ± 0.002. Comparison to previous work from this laboratory for the reaction of CF3CH2CHCl with CF3 radicals shows that substitution of Cl for H increases the kd /kc by about 50%; however, for the auto disproportionation-combination of CF3CH2CH2 radicals the chlorine substituent decreases the observed rate constant ratio by a factor of two. The chlorine substituent effect on the observed kd /kc ratios is compared to predictions from molecular orbital calculations. © 1996 John Wiley & Sons, Inc. 相似文献
8.
Yin Shuhui Liu Hongping Zhang Jianyang Jiang Bo Wang Li Sha Guohe Lou Nanquan 《化学物理学报(中文版)》2003,16(1):3-8
The multi-photon dissociative photoionization dynamics of CF3I has been studied with femtosecond two-color pump-probe time of flight mass spectra at a pump pulse of 265 nm and a probe pulse of 398 nm. The life constants of CF3I+ and its fragment ions CF3+ and I+ are obtained as (96±7), (198±130) and (167±6)fs, respectively. The multi-photon dynamics leading to these ions differ. CF3I+ corresponds to a (1+2′) transition with one-photon pump excitation to the A band of CF3I. CF3+ are mainly formed by a tow-photon probe excitation to the CF3+ with subsequent dissociation of parent ions. I+ are produced in (2+2′) combined with (1+1′+2′) process. The results provide information on the multi-photon pathways involved. 相似文献
9.
The dissociative photoionization of molecular‐beam cooled CH2CO in a region of ?10–20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH2CO+ and of observed fragment ions CH2+, CHCO+, HCO+, C2O+, CO+, and C2H2+ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH2CO are computed with the Gaussian‐3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C‐H bonds to form CH2+ + CO and CHCO+ + H, respectively; at greater energies, dissociation involving H migration takes place. 相似文献
10.
Rate constant ratios, kd/kc for the disproportionation/combination reaction have been measured as 0.07 ± 0.02 when an H is removed from the CH2 position of the CF3CH2CHCH3 radical and as 0.24 ± 0.03 when the H is removed from the CH3 position in the reaction with the CF3 radical. For the self‐reaction between two CF3CH2CHCH3 radicals, kd/kc has been measured as 0.27 ± 0.03 when the H is removed from the CH2 position and as 0.47 ± 0.04 when the H is removed from the CH3 position. The branching fraction, corrected for the number of hydrogens at each site, is 0.70 favoring the methyl position when the acceptor radical is CF3 and 0.54 when CF3CH2CHCH3 is the acceptor radical. Branching fraction results show that the CF3 substituent on the CF3CH2CHCH3 radical hinders disproportionation when CF3 is the acceptor radical. When the accepting radical is CF3CH2CHCH3 the CF3 substituent may slightly impede the disproportionation reaction, but the branching ratio is nearly statistical. The effect of substituents on the donor radical, CF3CH2CHX, will be discussed for the series X = H, CF3, Cl, and CH3 when the acceptor radical is CF3. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 549–557, 2001 相似文献
11.
Laffineur F Auguste D Plumier F Pirlot C Hevesi L Delhalle J Mekhalif Z 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3240-3245
In this paper, two monolayers self-assembled on a silver substrate are compared: a monolayer of n-hexadecanethiol and a monolayer of n-11-perfluorobutylundecanethiol. The protecting properties of both monolayers have been extensively studied by X-ray photoelectron spectroscopy, contact angle, polarization modulation infrared reflection absorption spectroscopy, conventional electrochemical techniques (polarization curves and electrochemical impedance spectroscopy), and scanning vibrating electrode technique. Both monolayers were successfully self-assembled but organization is slightly different, the fluorinated segment introduces small disorganization. Nevertheless, good homogeneous corrosion protection is observed for each monolayer. 相似文献
12.
13.
Urata S Tsuzuki S Takada A Mikami M Uchimaru T Sekiya A 《Journal of computational chemistry》2004,25(3):447-459
The intermolecular interaction energy curves of CH(3)OCH(3)-CH(2)F(2), CF(3)OCH(3)-CH(2)F(2), CF(3)OCF(3)-CH(2)F(2), CH(3)OCH(3)-CHF(3), CF(3)OCH(3)-CHF(3), and CF(3)OCF(3)-CHF(3) complexes were calculated by the MP2 level ab initio molecular orbital method using the 6-311G** basis set augmented with diffuse polarization functions. We investigate the fluorine substitution effects of both methane and dimethyl ether on intermolecular interactions. In addition, orientation dependence of intermolecular interaction energies is also studied with utilizing eight types of orientations. Our analyses demonstrate that partial fluorinations of methane make electrostatic interaction dominant, and consequently enhance attractive interaction at several specific orientations. On the contrary, fluorine substitutions of dimethyl ether substantially decrease the electrostatic interaction between ether and CH(2)F(2) or CHF(3); thus, there is no such characteristic interaction between the C-H of fluorinated methane and ether oxygen of CF(3)OCF(3) as conventional hydrogen bonding, due to reduced polarity of fluorinated ether. The combination of different pairs of the electrostatic interaction is therefore responsible for the intermolecular interaction differences among the complexes investigated herein and also their orientations. 相似文献
14.
Burgin MO Jr JG Heard GL Setser DW Holmes BE 《The journal of physical chemistry. A》2007,111(12):2283-2292
Chemically activated CF2ClCHFCH3 and CF2ClCHFCD3 molecules were prepared with 94 kcal mol-1 of vibrational energy by the recombination of CF2ClCHF and CH3(CD3) radicals at room temperature. The unimolecular reaction pathways were 2,3-FH(FD) elimination, 1,2-ClF interchange and 1,2-ClH elimination; the interchange produces CF3CHClCH3(CF3CHClCD3) with 105 kcal mol-1 of vibrational energy. Rate constants for CF2ClCHFCH3 [CF2ClCHFCD3] were (3.1+/-0.4)x10(6) s-1 [(1.0+/-0.1)x10(6) s-1] for 2,3-FH [FD] loss, (1.5+/-0.2)x10(6) s-1 [(8.3+/-0.9)x10(5) s-1] for 1,2-ClF interchange, and (8.2+/-1.0)x10(5) s-1 [(5.3+/-0.6)x10(5) s-1] for 1,2-ClH [DCl] loss. These correspond to branching fractions of 0.55+/-0.06 [0.43+/-0.04] for 2,3-FH [FD] loss, 0.29+/-0.03 [0.35+/-0.04] for 1,2-ClF interchange, and 0.16+/-0.02 [0.22+/-0.02] for 1,2-ClH [ClD] loss. Kinetic-isotope effects were 3.0+/-0.6 for 2,3-FH [FD] loss, 1.6+/-0.3 for 1,2-ClH loss, and 1.8+/-0.4 for 1,2-ClF interchange. The CF3CHClCH3 (CF3CHClCD3) molecules formed by 1,2-FCl interchange react by loss of HCl [DCl] with rate constants of (5.6+/-0.9)x10(7) s-1 [(2.1+/-0.4)x10(7)] s-1 for an isotope effect of 2.7+/-0.4. Density functional theory was employed to calculate vibrational frequencies and moments of inertia for the molecules and for the transition-state structures. These results were used with RRKM theory to assign threshold energies from comparison of computed and experimental unimolecular rate constants. The threshold energy for ClF interchange is 57.5 kcal mol-1, and those for HF and HCl channels are 2-5 kcal mol-1 higher. Experiments with vibrationally excited CF2ClCF2CF3, CF2ClCF2CF2Cl, and CF2ClCF2Cl, which did not show evidence for ClF interchange, also are reported. 相似文献
15.
Rate constant ratios, kd/kc, for the disproportionation/combination reaction at a temperature of 295 ± 2 K, have been measured as 0.034 ± 0.009 for the collision between CF3CH2CF2 + CF3 radicals and as 0.075 ± 0.019 for CF3CH2CF2 + CF3CH2CF2 radicals. The effect of the two fluorine substituents on the rate constant ratio is compared to previous kd/kcs with CF3CH2CH2, CF3CH2CHCl, and CF3CH2CHCF3 radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 237–243, 1999 相似文献
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17.
Hui Zhang Gui‐Ling Zhang Jing‐Yao Liu Miao Sun Bo Liu Ze‐Sheng Li 《Journal of computational chemistry》2010,31(15):2794-2803
The multiple‐channel reactions OH + CH3SCH3 → products, CF3 + CH3SCH3 → products, and CH3 + CH3SCH3 → products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for eight reaction channels are calculated by the improved canonical variational transition state theory with small‐curvature tunneling contribution over the temperature range 200–3000 K. The total rate constants are in good agreement with the available experimental data and the three‐parameter expressions k1 = 4.73 × 10?16T1.89 exp(?662.45/T), k2 = 1.02 × 10?32T6.04 exp(933.36/T), k3 = 3.98 × 10?35T6.60 exp(660.58/T) (in unit of cm3 molecule?1 s?1) over the temperature range of 200–3000 K are given. Our calculations indicate that hydrogen abstraction channels are the major channels and the others are minor channels over the whole temperature range. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
18.
Gonzalez-Lafont A Lluch JM Varela-Alvarez A Sordo JA 《The journal of physical chemistry. B》2008,112(2):328-335
Variational transition-state theory rate constants with multidimensional tunneling contributions using the small curvature method have been calculated for the CF3CH2CH3 (HFC-263fb) + OH reaction over a temperature range from 200 to 373 K. The mPW1B95-41.0 hybrid functional, parametrized by Albu and Swaminathan to generate theoretical rate constants nearly identical to the experimental values for the CH3F + OH reaction, has been used in conjunction with the 6-31+G** basis set to explore the potential energy surface of the title reaction. The good agreement found between theoretical predictions and the experimental data available suggests that the present approach is an excellent option to obtain high-quality results at low computational cost for direct dynamics studies of hydrogen abstraction reactions from complex hydrofluorocarbons. The reliability of the structure activity relationship used to estimate rate constant values for OH reactions with hydrofluorocarbons is also discussed in detail. 相似文献
19.
Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2 using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl2 in a mixture containing the ether and CD4. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD4 → DCl + CD3. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF3CH2OCHF2: k = (5.15 ± 0.7) × 10−12 exp(−1830 ± 410 K/T) cm3 molecule−1 s−1 Cl + CF3CHClOCHF2: k = (1.6 ± 0.2) × 10−11 exp(−2450 ± 250 K/T) cm3 molecule−1 s−1 Cl + CF3CH2OCClF2: k = (9.6 ± 0.4) × 10−12 exp(−2390 ± 190 K/T) cm3 molecule−1 s−1 The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001 相似文献
20.
The CO_2 laser induced room temperature reactions of CH_3CF_2H or another protium-donorCH_3CHClCH_3 with chlorine-atom donors (Z--Cl) CFCl_2CF_2Cl, CF_3CCl_3, CFCl_3 or CF_2Cl_2, havebeen investigated. Some of these reactions can yield two important monomers (CF_2=CH_2 andCF_2=CFCl) for fluoropolymers simultaneously. The yield dependence of these two alkenes on experi-mental conditions has been studied. A laser-initiated chain process is supported by identifica-tion of Z--H intermediates in these reactions. 相似文献