Ideal gas thermodynamic properties of CH4−(a+b+c+d)FaClbBrcId Halomethanes

Kudchadker, Shanti A.; Kudchadker, Arvind P.

doi:10.1063/1.555585

Cited by 40 publications

(24 citation statements)

References 42 publications

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“…Few experimental data are available for the mixed species so both Kudchadker and Kudchadker 45 Table 4 can be used to derive a wealth of carbon-hydrogen and carbon-halogen bond strengths. Here we focus on C-H bonds and list the results for D 298 in the same table.…”

Section: Resultsmentioning

confidence: 99%

A Computational Study of the Thermochemistry of Bromine- and Iodine-Containing Methanes and Methyl Radicals

2005

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Bromo-and iodomethanes and the corresponding halogenated methyl radicals have been investigated by ab initio methods. Geometries and vibrational frequencies were derived with quadratic configuration interaction methods at the QCISD/6-311G(d,p) level of theory, and energies via QCISD(T)/6-311+G(3df,2p). Core electrons were represented with relativistic effective potentials. Anharmonicity of the out-of-plane bending modes in the methyl radicals was taken into account by numerical integration of the Schrödinger equation with potentials derived from relaxed scans of these modes. The results are in good accord with experimental data where available. Thermochemistry derived via isodesmic reactions referenced to CH 3 , CH 4 , and monohalomethanes yields excellent accord with new experiments on dihalomethanes and provides recommendations for the more poorly characterized tri-and tetrahalomethanes and halomethyl radicals. For the methanes CH 2 Br 2 , CHBr 3 , CBr 4 , CH 2 I 2 , CHI 3 , CI 4 , CH 2 BrI, CHBr 2 I, and CHBrI 2 we compute ∆ f H°2 98 values of 4.3, 51.6, 110.6, 108.1, 208.5, 321.3, 56.8, 104.8, and 157.1 kJ mol -1 , respectively. For the methyl radicals CH 2 Br, CHBr 2 , CBr 3 , CH 2 I, CHI 2 , CI 3 , CHBrI, CBr 2 I, and CBrI 2 we compute ∆ f H°2 98 values of 166.6, 191.7, 224.0, 217.2, 290.4, 369.1, 241.6, 320.8, and 272.3 kJ mol -1 , respectively. Recommended confidence limits are (3 kJ mol -1 per Br or I atom. Trends in these values and the corresponding C-H bond strengths are discussed and compared with prior experiments, empirical estimation schemes, and ab initio calculations.

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Section: Resultsmentioning

confidence: 99%

A Computational Study of the Thermochemistry of Bromine- and Iodine-Containing Methanes and Methyl Radicals

2005

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“…For these species, carefully reviewed ∆H f° values from the Journal of Physical and Chemical Reference Data (JPCRD) were generally utilized (Chao et al 1973Rodgers et al, 1974;Chen et al, 1975Chen et al, , 1976Kudchadker and Kudchadker, 1975, 1978, 1979. The one exception to this rule was the choice of the more recent values of Kolesov and Papina (Papina et al, 1982;Kolesov and Papina, 1983;Papina and Kolesov, 1987) over earlier values provided in the JPCRD.…”

Section: Closed-shell Speciesmentioning

confidence: 98%

Calculated One- and Two-Electron Reduction Potentials and Related Molecular Descriptors for Reduction of Alkyl and Vinyl Halides in Water

Totten

Roberts

2001

Critical Reviews in Environmental Science and Technology

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One-and two-electron reduction potentials (E 1 and E 2 values) were calculated from published thermodynamic data for 39 halogenated C 1 and C 2 compounds, including many commonly encountered groundwater contaminants. Because reductive dehalogenation is an important pathway for their destruction under anaerobic conditions, information concerning the relevant reduction potentials may be useful for assessing the thermodynamic feasibility of a particular reaction, as well as in developing linear free energy relationships (LFERs) or other quantitative structure-activity relationships (QSARs) that may enable prediction of rates of transformation. E 1 values were calculated assuming a stoichiometry corresponding to dissociative electron transfer, which produces a carbon-centered radical and a halide ion. E 2 values were calculated for both hydrogenolysis and reductive β-elimination reactions. Uncertainties in the thermodynamic data for the organohalides under consideration may introduce substantial uncertainty in the resulting E 1 values. Hence, relationships between calculated E 1 values and various surrogate parameters were also investigated. E 1 values were correlated with lowest unoccupied molecular orbital (LUMO) energies and carbon-halogen homolytic bond dissociation energies (BDE values), which were computed via density functional theory. Correlations were also attempted between E 1 values and vertical attachment energies (VAE values), the latter representing experimental measures of the ease of reduction of a molecule to a radical anion in the gas phase. These alternate descriptors may provide a means for estimating E 1 . Additional studies will need to be undertaken to establish which descriptor best correlates with reactivity in environmental reductive dehalogenation.

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“…For CH 2 BrI, a single 271.6 nm (4.57 eV) photon is sufficient to overcome the C-I and C-Br dissociation thresholds at 2.39 eV and 2.94 eV, and to induce IBr elimination (3.84 eV). Secondary or three-body dissociations, by contrast, require two UV photons to create CH 2 , I, and Br (5.66 eV) [28,37,38]. Fragment momenta measured following neutral photodissociation will reflect these thresholds and the energy deposited into internal photofragment states.…”

Section: Introductionmentioning

confidence: 99%

Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics

Burt¹,

Boll²,

Lee³

et al. 2017

Phys. Rev. A

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The dynamics following laser-induced molecular photodissociation of gas-phase CH 2 BrI at 271.6 nm were investigated by time-resolved Coulomb explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH 2 BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of CH 2 Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb explosion imaging as a real-time probe of chemical dynamics.2

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Ideal gas thermodynamic properties of CH4−(a+b+c+d)FaClbBrcId Halomethanes

Cited by 40 publications

References 42 publications

A Computational Study of the Thermochemistry of Bromine- and Iodine-Containing Methanes and Methyl Radicals

A Computational Study of the Thermochemistry of Bromine- and Iodine-Containing Methanes and Methyl Radicals

Calculated One- and Two-Electron Reduction Potentials and Related Molecular Descriptors for Reduction of Alkyl and Vinyl Halides in Water

Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics

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