765 research outputs found
Velocity map imaging of the dynamics of the CH3 + HCl -> CH4 + Cl reaction using a dual molecular beam method
International audienceThe reactions CH3 + HCl → CH4 + Cl(<sup>2</sup>P<sub>3/2</sub>) and CD<sub>3</sub> + HCl → CD<sub>3</sub>H + Cl(<sup>2</sup>P<sub>3/2</sub>) have been studied by photo-initiation (by CH<sub>3</sub>I or CD<sub>3</sub>I photolysis at 266 nm) in a dual molecular beam apparatus. Product Cl(<sup>2</sup>P</sub>3/2</sub>) atoms were detected using resonance enhanced multi-photon ionisation and velocity map imaging, revealing product translational energy and angular scattering distributions in the centre-of-mass frame. Image analysis is complicated by the bimodal speed distribution of CH<sub>3</sub> (and CD<sub>3</sub>) radicals formed in coincidence with I(<sup>2</sup>P<sub>3/2</sub>) and I(<sup>2</sup>P<sub>1/2</sub>) atoms from CH<sub>3</sub>I (CD<sub>3</sub>I) photodissociation, giving overlapping Newton diagrams with displaced centre of mass velocities. The relative reactivities to form Cl atoms are greater for the slower CH<sub>3</sub> speed group than the faster group by factors of ~1.5 for the reaction of CH<sub>3</sub> and ~2.5 for the reaction of CD<sub>3</sub>, consistent with the greater propensity of the faster methyl radicals to undergo electronically adiabatic reactions to form Cl(<sup>2</sup>P<sub>1/2</sub>). The average fraction of the available energy becoming product translational energy is = 0.48 ± 0.05 and 0.50 ± 0.03 for reaction of the faster and slower sets of CH<sub>3</sub> radicals, respectively. The Cl atoms are deduced to be preferentially forward scattered with respect to the HCl reagents, but the angular distributions from the dual beam imaging experiments require correction for under-detection of forward scattered Cl products
Product energy deposition of CN plus alkane H abstraction reactions in gas and solution phases
Photochemical reaction dynamics of 2,2'-dithiobis(benzothiazole):direct observation of the addition product of an aromatic thiyl radical to an alkene with time-resolved vibrational and electronic absorption spectroscopy
Photochemical reaction dynamics of 2,2'-dithiobis(benzothiazole):direct observation of the addition product of an aromatic thiyl radical to an alkene with time-resolved vibrational and electronic absorption spectroscopy
Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution
Direct Observation of Ylide and Enol Intermediates Formed in Competition with Wolff Rearrangement of Photo-Excited Ethyl Diazoacetoacetate
Velocity map imaging of the dynamics of reactions of Cl atoms with neopentane and tetramethyl silane
A parallel multistate framework for atomistic non-equilibrium reaction dynamics of solutes in strongly interacting organic solvents
We describe a parallel linear-scaling computational framework developed to
implement arbitrarily large multi-state empirical valence bond (MS-EVB)
calculations within CHARMM. Forces are obtained using the Hellman-Feynmann
relationship, giving continuous gradients, and excellent energy conservation.
Utilizing multi-dimensional Gaussian coupling elements fit to CCSD(T)-F12
electronic structure theory, we built a 64-state MS-EVB model designed to study
the F + CD3CN -> DF + CD2CN reaction in CD3CN solvent. This approach allows us
to build a reactive potential energy surface (PES) whose balanced accuracy and
efficiency considerably surpass what we could achieve otherwise. We use our PES
to run MD simulations, and examine a range of transient observables which
follow in the wake of reaction, including transient spectra of the DF
vibrational band, time dependent profiles of vibrationally excited DF in CD3CN
solvent, and relaxation rates for energy flow from DF into the solvent, all of
which agree well with experimental observations. Immediately following
deuterium abstraction, the nascent DF is in a non-equilibrium regime in two
different respects: (1) it is highly excited, with ~23 kcal mol-1 localized in
the stretch; and (2) not yet Hydrogen bonded to the CD3CN solvent, its
microsolvation environment is intermediate between the non-interacting
gas-phase limit and the solution-phase equilibrium limit. Vibrational
relaxation of the nascent DF results in a spectral blue shift, while relaxation
of its microsolvation environment results in a red shift. These two competing
effects result in a post-reaction relaxation profile distinct from that
observed when DF vibration excitation occurs within an equilibrium
microsolvation environment. The parallel software framework presented in this
paper should be more broadly applicable to a range of complex reactive systems.Comment: 58 pages and 29 Figure
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