Vibrational relaxation of HOD by collisions with Ar atoms.

Vibrational relaxation of HOD(v12, v3) molecules by collisions with Ar was studied at 298 K (v12 denotes coupled bending, v2, and OD stretching, v1, vibrational modes and v3 denotes OH stretching mode). The vibrationally excited HOD molecules were generated by exothermic abstraction reactions of OD radicals with 13 different RH reactants and observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations for vibrational populations.

Vibrational relaxation of high levels of HO by collisions with Ar as studied by infrared chemiluminescence.

Vibrational relaxation of HO(v,v) molecules by collisions with Ar was studied at 298 K (v denotes the bending vibrational mode and v denotes the sum of the symmetric, v, and asymmetric, v, vibrational modes). The HO molecules from 14 different exothermic reactions of H-atom abstraction by OH radicals were observed by infrared emission from a fast flow reactor as a function of Ar pressure and reaction time. Numerical kinetic calculations were used to obtain rate constants for stretch-to-bend energy conversion, (v,v) → (v + 2,v - 1), and pure bend relaxation, (v,v) → (v - 1,v).

Unimolecular HBr and HF Elimination Reactions of Vibrationally Excited CHCHBr and CDCHFBr: Identification of the 1,1-HBr Elimination Reaction from CDCHFBr and Search for the CD(F)C:HBr Adduct.

Chemical activation experiments and computational methods have been used to study the unimolecular reactions of CHCHBr and CDCHFBr with 90 and 93 kcal mol of vibrational energy, respectively. The four-centered elimination reactions of HBr and DBr are the dominant reactions; however, 2,1-DF, 1,1-HBr, and 1,1-HF reactions are also observed from CDCHFBr. The main focus was to search for the role of the CD(F)C:HBr adduct in the 1,1-HBr elimination for comparison with carbene adducts in 1,1-HX(Y) elimination from RCHXY (X,Y = Cl and F) molecules.

Experimental and Computational Studies of Unimolecular 1,1-HX (X = F, Cl) Elimination Reactions of CDCHFCl: Role of Carbene:HF and HCl Adducts in the Exit Channel of RCHFCl and RCHCl Reactions.

The gas-phase unimolecular reactions of CDCHFCl molecules with 94 kcal mol of vibrational energy have been studied by the chemical-activation experimental technique and by electronic-structure computations. Products from the reaction of CDCHFCl molecules, formed by the recombination of CD and CHFCl radicals in a room temperature bath gas, were measured by gas chromatography-mass spectrometry. The 2,1-DCl (81%) and 1,1-HCl (17%) elimination reactions are the principal processes, but 2,1-DF and 1,1-HF elimination reactions also are observed.

Analysis of the Five Unimolecular Reaction Pathways of CDClCHFCl with Emphasis on CDCl(F)C: and CDCl(Cl)C: Formed by 1,1-HCl and 1,1-HF Elimination.

The five unimolecular HX and DX (X = F, Cl) elimination pathways of CDClCHFCl* were examined using a chemical activation technique; the molecules were generated with 92 kcal mol of vibrational energy in a room-temperature bath gas by a combination of CDCl and CHFCl radicals. The total unimolecular rate constant was 9.7 × 10 s, and branching fractions for each channel were 0.

Infrared Chemiluminescence Study of the Reaction of Hydroxyl Radical with Formamide and the Secondary Unimolecular Reaction of Chemically Activated Carbamic Acid.

Reactions of OH and OD radicals with NHCHO and NDCHO were studied by Fourier transform infrared emission spectroscopy of the product molecules from a fast-flow reactor at 298 K. Vibrational distributions of the HOD and HO molecules from the primary reactions with the C-H bond were obtained by computer simulation of the emission spectra. The vibrational distributions resemble those for other direct H atom abstraction reactions, such as with acetaldehyde.

Post-transition state dynamics and product energy partitioning following thermal excitation of the F⋯HCHCN transition state: Disagreement with experiment.

Born-Oppenheimer direct dynamics simulations were performed to study atomistic details of the F + CHCN → HF + CHCN H-atom abstraction reaction. The simulation trajectories were calculated with a combined M06-2X/MP2 algorithm utilizing the 6-311++G** basis set. The experiments were performed at 300 K, and assuming the accuracy of transition state theory (TST), the trajectories were initiated at the F⋯HCHCN abstraction TS with a 300 K Boltzmann distribution of energy and directed towards products.

The Unimolecular Reactions of CFCHF Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules.

The recombination of CF and CHF radicals in a room-temperature bath gas was used to prepare vibrationally excited CFCHF* molecules with 101 kcal mol of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF, CF(F)C: and CF product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF(F)C: concentration was measured by trapping the carbene with trans-2-butene.

Chemical Activation Study of the Unimolecular Reactions of CDCDCHCl and CHClCHCl with Analysis of the 1,1-HCl Elimination Pathway.

Chemically activated CDCHCl molecules were generated with 88 kcal mol of vibrational energy by the recombination of CD and CHCl radicals in a room temperature bath gas. The competing 2,1-DCl and 1,1-HCl unimolecular reactions were identified by the observation of the CDCD═CHCl and CDCD═CDCl products. The initial CDCDC-Cl carbene product from 1,1-HCl elimination rearranges to CDCD═CDCl under the conditions of the experiments.

Branching Ratios and Vibrational Distributions in Water-Forming Reactions of OH and OD Radicals with Methylamines.

Reactions of OH and OD radicals with (CH3)3N, (CH3)2NH, and CH3NH2 were studied by Fourier transform infrared emission spectroscopy (FTIR) of the water product molecules from a fast-flow reactor at 298 K. The rate constants (4.4 ± 0.

Characterization of the 1,1-HCl Elimination Reaction of Vibrationally Excited CD3CHFCl Molecules and Assignment of Threshold Energies for 1,1-HCl and 1,2-DCl plus 1,1-HF and 1,2-DF Elimination Reactions.

Vibrationally excited CD3CHFCl molecules with 96 kcal mol(-1) of energy were generated by the recombination of CD3 and CHFCl radicals in a room-temperature bath gas. The four competing unimolecular decomposition reactions, namely, 1,1-HCl and 1,2-DCl elimination and 1,1-HF and 1,2-DF elimination, were observed, and the individual rate constants were measured. The product branching fractions are 0.

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD3CD2CHF2.

The recombination of CHF2 and C2D5 radicals was used to produce CD3CD2CHF2* molecules with 96 kcal mol(-1) of vibrational energy in a room temperature bath gas. The formation of CD3CD═CHF and CD3CD═CDF was used to identify the 1,2-DF and 1,1-HF unimolecular elimination channels; CD3CD═CDF is formed by isomerization of the singlet-state CD3CD2CF carbene. The total unimolecular rate constant is 1.

Unimolecular reactions of 1,1,1-trichloroethane, 1,1,1-trichloropropane, and 3,3,3-trifluoro-1,1,1-trichloropropane: determination of threshold energies by chemical activation.

The recombination of CCl3 radicals with CH3, CH3CH2, and CF3CH2 radicals was used to generate CH3CCl3, CH3CH2CCl3, and CF3CH2CCl3 molecules with approximately 87 kcal mol(-1) of vibrational energy in a bath gas at room temperature. The competition between collisional deactivation and unimolecular reaction by HCl elimination was used to obtain the experimental rate constants for each molecule. These experimental rate constants were matched to calculated statistical unimolecular rate constants to assign threshold energies to the three HCl elimination reactions.

Effects of CF(3) and CH(3) groups on the threshold energy for the unimolecular interchange reaction of Cl- and F-atoms in CF(3)CHFCH(2)Cl and CH(3)CHFCH(2)Cl.

The recombination reactions of CH2Cl radicals with CF3CHF and with CH3CHF radicals were used to generate CF3CHFCH2Cl and CH3CHFCH2Cl molecules with 90-92 kcal mol(-1) of vibrational energy. The experimental rate constants for elimination of HCl and HF and the interchange of Cl and F atoms were measured and compared to RRKM calculated rate constants to assign the threshold energy for each unimolecular reaction channel. The Cl/F interchange reaction is approximately 18% of the total unimolecular reaction for both molecules.

Unimolecular isomerization of CH2FCD2Cl via the interchange of Cl and F atoms: assignment of the threshold energy to the 1,2-dyotropic rearrangement.

The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FCD2Cl molecules with 91 kcal mol(-1) of vibrational energy. Three unimolecular processes are in competition with collisional deactivation of CH2FCD2Cl; HCl and DF elimination to give CHF═CD2 and CH2═CDCl plus isomerization to give CH2ClCD2F by the interchange of F and Cl atoms. The Cl/F interchange reaction was observed, and the rate constant was assigned from measurement of CHCl═CD2 as a product, which is formed by HF elimination from CH2ClCD2F.

Isomerisation of CF2ClCH2Cl and CFCl2CH2F by interchange of Cl and F atoms with analysis of the unimolecular reactions of both molecules.

The recombination of CF(2)Cl with CH(2)Cl and CFCl(2) with CH(2)F were employed to generate CF(2)ClCH(2)Cl* and CFCl(2)CH(2)F* 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 CFCl(2)CH(2)F were 2.

Unimolecular reactions in the CF3CH2Cl ↔ CF2ClCH2F system: isomerization by interchange of Cl and F atoms.

The recombination of CF(2)Cl and CH(2)F radicals was used to prepare CF(2)ClCH(2)F* molecules with 93 ± 2 kcal mol(-1) of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF(2)═CHF, (2) isomerization to CF(3)CH(2)Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl═CHF. Since the isomerization reaction is 12 kcal mol(-1) exothermic, the CF(3)CH(2)Cl* molecules have 105 kcal mol(-1) of internal energy and they can eliminate HF to give CF(2)═CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF(2)ClCH(2)F.

Isomerization of neopentyl chloride and neopentyl bromide by a 1,2-interchange of a halogen atom and a methyl group.

The recombination of chloromethyl and t-butyl radicals at room temperature was used to generate neopentyl chloride molecules with 89 kcal mol(-1) of internal energy. The observed unimolecular reactions, which give 2-methyl-2-butene and 2-methyl-1-butene plus HCl, as products, are explained by a mechanism that involves the interchange of a methyl group and the chlorine atom to yield 2-chloro-2-methylbutane, which subsequently eliminates hydrogen chloride by the usual four-centered mechanism to give the observed products. The interchange isomerization process is the rate-limiting step.

Unimolecular reactions of CH(2)BrCH(2)Br, CH(2)BrCH(2)Cl, and CH(2)BrCD(2)Cl: identification of the Cl-Br interchange reaction.

The recombination reactions of CH(2)Br and CH(2)Cl radicals have been used to generate vibrationally excited CH(2)BrCH(2)Br and CH(2)BrCH(2)Cl molecules with 91 kcal mol(-1) of energy in a room-temperature bath gas. The experimental unimolecular rate constants for elimination of HBr and HCl were compared to calculated statistical rate constants to assign threshold energies of 58 kcal mol(-1) for HBr elimination from C(2)H(4)Br(2) and 58 and 60 kcal mol(-1), respectively, for HBr and HCl elimination from C(2)H(4)BrCl. The Br-Cl interchange reaction was demonstrated and characterized by studying the CH(2)BrCD(2)Cl system generated by the recombination of CH(2)Br and CD(2)Cl radicals.

Unimolecular HCl and HF elimination reactions of 1,2-dichloroethane, 1,2-difluoroethane, and 1,2-chlorofluoroethane: assignment of threshold energies.

The recombination of CH(2)Cl and CH(2)F radicals generates vibrationally excited CH(2)ClCH(2)Cl, CH(2)FCH(2)F, and CH(2)ClCH(2)F molecules with about 90 kcal mol(-1) of energy in a room temperature bath gas. New experimental data for CH(2)ClCH(2)F have been obtained that are combined with previously published studies for C(2)H(4)Cl(2) and C(2)H(4)F(2) to define reliable rate constants of 3.0 x 10(8) (C(2)H(4)F(2)), 2.

Characterization of the unimolecular water elimination reaction from 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol.

The unimolecular reactions of 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol have been studied by the chemical activation technique. The recombination of CH3, CD3, CF3, and CH2Cl radicals with CH2CH2OH radicals at room temperature was used to generate vibrationally excited CH3CH2CH2OH, CD3CH2CH2OH, CF3CH2CH2OH, and CH2ClCH2CH2OH molecules. The principal unimolecular reaction for propanol and propanol-d3 with 90 kcal mol(-1) of vibrational energy is 1,2-H2O elimination with rate constants of 3.

Unimolecular reactions of CF2ClCFClCH2F and CF2ClCF2CH2Cl: observation of ClF interchange.

The unimolecular reactions of CF(2)ClCFClCH(2)F and CF(2)ClCF(2)CH(2)Cl molecules formed with 87 and 91 kcal mol(-1), respectively, of vibrational energy from the recombination of CF(2)ClCFCl with CH(2)F and CF(2)ClCF(2) with CH(2)Cl at room temperature have been studied by the chemical activation technique. The 2,3- and 1,2-ClF interchange reactions compete with 2,3-ClH and 2,3-FH elimination reactions. The total unimolecular rate constant for CF(2)ClCF(2)CH(2)Cl is 0.

Unimolecular elimination of HF and HCl from chemically activated CF3CFClCH2Cl.

The unimolecular reactions of CF3CFClCH2Cl molecules formed with 87 kcal mol(-1) of vibrational energy by recombination of CF3CFCl and CH2Cl radicals at room temperature have been characterized by the chemical activation technique. The 2,3-ClH and 2,3-FH elimination reactions, which have rate constants of (2.5 +/- 0.

Unimolecular reactions of chemically activated CF2BrCF2CH3 and CF2BrCF2CD3: evidence for 1,2-FBr interchange.

Vibrationally excited CF2BrCF2CH3 and CF2BrCF2CD3 molecules were prepared with 96 kcal mol-1 energy at room temperature by the recombination of CF2BrCF2 and CH3 (CD3) radicals. The observed unimolecular reactions are 1,2-BrF interchange to give CF3CFBrCH3 (CD3) molecules and 2,3-FH (FD) elimination; the rate constants are 2.2 x 10(5) (1.