- Pressure Dependence of the Rate Constants for the Reactions CH3 + O2 and CH3 + NO from 3 to 10E4 Torr
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A relative rate technique is used to measure the pressure dependence of the rate constants for reaction 1 (CH3 + O2 + M -> CH3O2 + M) and reaction 3 (CH3 + NO + M -> CH3NO + M) relative to reaction 2 (CH3 + Cl2 -> CH3Cl + Cl).The pressure dependence of the rate constant of reaction 3 at 297 K can be represented in the Troe equation by the parameters (k3)0 = (3.5 +/- 0.4)E-30 cm6 molecule-2 s-1, (k3)infinite = (1.68 +/- 0.1)E-11 cm3 molecule-1 s-1, and Fcent = 0.46.The values of k3 are identical to those observed in recent absolute rate measurements at 296 K and 27-600 Torr, verifying that the rate constant chosen for reaction 2, k2 = 3.95E-12 exp(-530/RT), is both pressure independent and correct at 296 K.This value of k2 was used to determine absolute values of k1 from the k1/k2 in N2 diluent for pressures between 3 and 11000 Torr at 297 K, between 20 and 1500 Torr at 370 K, and between 40 and 1500 Torr at 264 K.All data in N2 can be fitted using the following parameters in the Troe equation: (k1)0 = (7.56 +/- 1.1)E-31 (T/300)-3.64+/-1.0 cm6 molecule-2 s-1; (k1)infinite = (1.31 +/- 0.1)E-12 (T/300)1.2+/-0.8 cm3 molecule-1 s-1; Fcent = 0.48 (264 K), 0.46 (297 K), 0.42 (370 K).Error limits include statistical error and the uncertainty in k2.In He, N2, and SF6 diluents the relative third-body efficiencies are 0.56 : 1.0 : 1.52, respectively, assuming that Fcent is independent of diluent.The high-pressure limit in SF6 is identical to that in N2.Rate constant ratios were also measured at 297 K for CD3 + O2 + M -> CD3O2 + M (1D) between 5 and 6000 Torr.Assuming that k2D = k2, the limiting rate constants using Fcent = 0.46 are (k1D)0 = (11.8 +/- 1.6)E-31 cm6 molecule-2 s-1 and (k1D)infinite = (1.38 +/- 0.08)E-12 cm3 molecule-1 s-1.
- Kaiser, E. W.
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p. 11681 - 11688
(2007/10/02)
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- Association Reaction of CH3 and NO: Evidence for the Involvement of the Triplet Surface
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The rate constant for the CH3 + NO reaction has been measured by laser flash photolysis/absorption spectroscopy over the temperature range 296-509 K and at pressures of 25-600 Torr.The data have been analysed using a global variant of the Troe factorisation technique which provides parameters for the representation of k1(P,T) over the experimental range.In addition, a further global technique for analysing the experimental data, based on inverse Laplace transformation of k1infinite(T), coupled with a master equation treatment, has been developed.The advantage of this approach is that it emphasises the relationship between the limiting high-pressure rate coefficient and the energy-dependent lifetime of the adduct.In the present reaction system, this approach enables the lowest triplet state to be implicated in the reaction; it is proposed that, following its formation, the triplet undergoes rapid intersystem crossing to the ground singlet state.The limiting rate parameters returned from the analysis are k1infinite = 1.5 x 10-11 exp(-60 K/T) cm3 mlecule-1 s-1, k10 = 6.9 x 10-32 exp(1430 K/T) cm6 molecule-2 s-1, down = 235 cm-1, for Ar as the diluent gas.
- Davies, Joanne W.,Green, Nicholas J. B.,Pilling, Michael J.
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p. 2317 - 2324
(2007/10/02)
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- Gas-Phase Reactions of Groups 8-10 Transition-Metal Ions with Nitroalkanes
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Fe(1+), Co(1+), and Ni(1+) exhibit a rich chemistry in their reactions with nitroalkanes.Oxidative addition of the metal ion into the C-N bond dominates the chemistry of Ni(1+).Fe(1+), however, preferentially attacks the stronger N-O and C-C bonds, while Co(1+) reacts in a manner intermediate to Fe(1+) and Ni(1+).An unusual reaction pathway for all three metals is an apparent nitro-to-nitrite isomerisation.In addition, following C-C insertion, radical loss processes dominate over processes involving β-hydrogen abstraction.The structures of the reaction products were probed by collision-induced dissociation and secondary ion-molecule reactions with the nitroalkane.The effect of total pressure on these reactions was also studied.Evidence is presented for a long-lived (>1 ms) reaction intermediate of C-N insertion which undergoes stabilising collision in the presence of a relatively high pressure (ca. 1e-5 torr) of an inert gas.
- Cassady, C.J.,Freiser, B.S.
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p. 1573 - 1580
(2007/10/02)
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