The vibrational enhancement factor in the Cl + CHD3(v1 = 1) reaction is revisited over the collisional energy range of 2-5.9 kcal mol(-1). Contrary to the previous results obtained by probing the low-|N, K⟩ states of CD3(v = 0) products, CH stretching excitation becomes more efficacious than the same amount of translational energy in promoting the HCl(v) + CD3(v = 0) product pairs when all-|N, K⟩ states are probed. Whereas the new vibrational enhancement factors, which are three to four times larger than the previous report, agree reasonably well with a recent reduced-dimensionality quantum dynamics calculation, a cautious note is made on the different initial |J,K⟩ rotational selections of the CHD3 reactants in the present theory-experiment comparison.

The effect of initial rotational states in the reaction of antisymmetric-excited CH4(v3=1,|jNl⟩) with Cl atom was investigated in a crossed-beam, product-imaging experiment over the collisional energy (Ec) range of 2-5 kcal mol(-1). We found that while the initial rotational excitations exert a noticeable effect on total reactivity, they leave little imprint on the more detailed product-state and angular distributions. This finding echoes the previous conclusion in the analogous Cl + CHD3(v1=1,|NK⟩) reaction. However, the rotational enhancement factor is substantial at low Ec and then becomes insignificant at higher Ec, in contrast to the Cl + CHD3 case. A more intriguing finding is the role of the vibrational angular momentum (l) in promoting the reactivity. A heuristic picture is proposed to rationalize the observations.

Exciting a stretching mode of a chemical bond should help its breaking during a chemical reaction, according to conventional wisdom. In several recent studies of the reactions of stretch-excited methane (and isotopologues) with the F atom, counterintuitively, we found that the induced reactant vibrations instead inhibit the bond rupture and slow down the overall reaction rate. This intriguing observation has been qualitatively ascribed to the vibrationally induced steric effects of the reaction in previous reports. However, quantitative determination of the reactivity suppression in terms of reaction cross sections remains lacking. In this report, we scrutinize the physical meaning of this (product) signal depletion phenomenon and fill the gap. Through a systematic investigation we further elucidate the additional reaction dynamics information that can be retrieved from the depletion measurements. The resultant rotationally state-selected reaction cross sections for both the vibrational ground and excited states are presented, and the stereodynamical implications are delineated.

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