ORCID Profile
0000-0002-2398-3914
Current Organisation
University of California, Irvine
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Publisher: AIP Publishing
Date: 08-03-2005
DOI: 10.1063/1.1869497
Abstract: Nonadiabatic dynamics in the title reaction have been investigated by 2+1 REMPI detection of the Cl(P3∕22) and Cl*(P1∕22) products. Reaction was initiated by photodissociation of CH3I at 266nm within a single expansion of a dilute mixture of CH3I and HCl in argon, giving a mean collision energy of 7800cm−1 in the center-of-mass frame. Significant production of Cl* was observed, with careful checks made to ensure that no additional photochemical or inelastic scattering sources of Cl* perturbed the measurements. The fraction of the total yield of Cl(PJ2) atoms formed in the J=12 level at this collision energy was 0.150±0.024, and must arise from nonadiabatic dynamics because the ground potential energy surface correlates to CH4+Cl(P3∕22) products.
Publisher: American Chemical Society (ACS)
Date: 04-11-2005
DOI: 10.1021/JP054627L
Abstract: A series of recent experimental and computational studies has explored how the dynamics of hydrogen abstraction from organic molecules are affected by the presence of functional groups in the molecule and by basic structural motifs such as strained ring systems. Comparisons drawn between reactions of Cl atoms with alkanes such as ethane, Cl + CH3CH3--> HCl + CH3CH2, which serve as benchmark systems, and with functionalized molecules such as alcohols, amines, and alkyl halides, Cl + CH3X --> HCl + CH2X (X = OH, NH2, halogen, etc.) expose a wealth of mechanistic detail. Although the scattering dynamics, as revealed from measured angular distributions of the velocities of the HCl with quantum-state resolution, show many similarities, much-enhanced rotational excitation of the HCl products is observed from reactions of the functionalized molecules. The degree of rotational excitation of the HCl correlates with the dipole moment of the CH2X radical and is thus attributed, at least in part, to post-transition-state dipole-dipole interactions between the separating, polar reaction products. This interpretation is supported by direct dynamics trajectories computed on-the-fly, and the HCl rotation is thus argued to serve as an in situ probe of the angular anisotropy of the reaction potential energy surface in the post-transition-state region. Comparisons between the dynamics of reactions of dimethyl ether and the three- and four-membered-ring compounds oxirane (c-C2H4O) and oxetane (c-C3H6O) raise questions about the role of reorientation of the reaction products on a time scale commensurate with their separation. The shapes and structures of polyatomic molecules are thus demonstrated to have important consequences for the stereodynamics of these direct abstraction reactions.
Publisher: American Chemical Society (ACS)
Date: 23-09-2021
Publisher: Wiley
Date: 20-12-2022
DOI: 10.1002/KIN.21625
Abstract: Temperature‐dependent rate constants for the reactions of CH 2 OO with acetone (Ac), biacetyl (BiAc), and acetylacetone (AcAc) have been measured over the range 275–335 K using a flash photolysis, transient absorption spectroscopy technique. The measurements were performed at a total pressure of ∼80 Torr in N 2 bath gas, which corresponds to the high‐pressure limit for these reactions. All three reactions show linear Arrhenius plots with negative temperature dependences. Rate constants increase in the order Ac AcAc « BiAc across the temperature range at 295 K the rate constants are k Ac = (4.8 ± 0.4) × 10 –13 cm 3 s –1 , k AcAc = (8.0 ± 0.7) × 10 –13 cm 3 s –1 , and k BiAc = (1.10 ± 0.09) × 10 –11 cm 3 s –1 . Sensitivity to temperature, characterized by the magnitude of the negative activation energy, increases in the order AcAc BiAc Ac ( E a / R values of –1830 ± 170 K, –1260 ± 170 K, and –460 ± 180 K, respectively). CBS‐QB3 calculations show that the Ac and BiAc reactions proceed via formation of an entrance channel complex followed by 1,3‐dipolar cycloaddition to form secondary ozonide products via a submerged transition state. For the BiAc reaction, the rate limiting step appears to be rearrangement of a long‐range van der Waals complex into the short‐range complex that subsequently leads directly to the cycloaddition transition state with a very low energy barrier. The calculations show that two reaction pathways are competitive for AcAc with nearly identical transition state free energies (Δ G ° = +10.1 kcal mol –1 at 298 K) found for cycloaddition at the C=O and at the C=C site of the dominant enolone tautomer. The weak temperature dependence observed is likely due to competition between these pathways.
Publisher: IOP Publishing
Date: 22-12-2005
Publisher: Informa UK Limited
Date: 07-2005
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Craig Murray.