Crossed‐Beam and Quantum Dynamics Studies of the Reaction Cl + CHD₃

Abstract

The ground‐state reaction of Cl + CHD3 was studied with joint experimental and theoretical efforts. Experiments were performed under crossed‐beam conditions using a time‐sliced velocity imaging detection method. By taking the images over the energy range of chemical significance—from threshold to about 9 kcal/mol—the reactive excitation functions as well as the dependence of product angular distributions and of the energy disposal on initial collision energies were obtained for both isotopic product channels. Theoretically, reduced dimensionality quantum dynamics calculations were performed for the HCl + CD3 channel, and the results are in excellent agreement with experimental findings. Comparisons with previously reported results on Cl + CH4/CD4, both experimental and theoretical, were also made to gain deeper insights into the dynamics of this benchmark atom + polyatomic reaction.

Imaging the Reaction Dynamics of O(3P)+CH4→OH+CH3

“…This behavior is in contrast to the analogous, endothermic reaction of Cl+CH 4 , in which the product distribution shifts sensitively and systematically toward the sideways/forward direction with incremental changes in E c . [24][25][26][27] For the product kinetic energy release, the bottom panels show a single peak in the product speed distributions, which is anticipated because energetically only the OHA C H T U N G T R E N N U N G (v'=0) products can be formed at collision energies of this work. The slight asymmetry of the distribution, bias towards the slower speed indicates small rotational excitations of the OHA C H T U N G T R E N N U N G (v'=0) products.…”

Reduced dimensionality spin-orbit dynamics of CH3 + HCl $\rightleftharpoons$⇌ CH4 + Cl on ab initio surfaces

“…7,16 Peripheral (high b) collisions lead to a so-called "stripping" mechanism with a more forward scattered distribution, 7,16,20 especially at high collision energies. 17,21,22 Reaction (2) is preferentially enhanced by excitation in both the C-H symmetric stretch and the umbrella excitation of the CH 4 group, whereas reaction (1) is enhanced by excitation of the H-Cl vibration but decreased by umbrella excitation of the CH 3 .…”

Perspective: Vibrational-induced steric effects in bimolecular reactions

“…Ab initio calculations 30,66,67 suggested a more product-like transition state structure (i.e., a late barrier) with the barrier height of ∼3.4 kcal mol −1 , in accord with the experimentally measured reaction threshold. 33,34 We note in passing that a late barrier for Cl + CHD 3 and a central barrier for O( 3 P) + CHD 3 are not inconsistent with the Hammond's postulate 4 or the Evans-Polanyi model. 1 The postulate or the model states that in a family of related reactions, the more exothermic the reaction is, the earlier the location of the barrier occurs along the reaction coordinate and the more the transition state will resemble the reagents.…”