Pair-Correlated Imaging of Cl + CH₃D(v₄, v₁-I, v₁-II = 1, |jK⟩) → CH₂D(v_i) + HCl(v)

Abstract

The title reactions were studied at a collisional energy of 10.0 kcal mol–1 in a crossed-beam, product-imaging experiment. In terms of integral cross sections, all three CH3-stretching excited CH3D­(v CH3 = 1) reagents promote the reactivity in forming the predominant product pair of (v CH2D, v HCl)s = (00, 0/1)s with a prominent mode-propensity of v 4 > v 1-I > v 1-II, where v 4 denotes the degenerate mode of CH3 asymmetric stretch and v 1-I and v 1-II are a pair of Fermi-coupled, symmetric-stretch states. The vibrationally excited CH2D product pairs of (61, 0)s, (11, 0)s, and (31, 0)s appear to be minor channels and display a reverse propensity of v 4 < v 1-I ≈ v 1-II for (61, 0)s, while v 4 > v 1-I for (11, 0)s. Based on the observed angular distributions, we conjecture that, irrespective of the initial mode of excitation, the (00, 0)s product pair proceeds by a direct abstraction of the peripheral type, whereas the (00,1)s pair is mediated via a resonance pathway. Intriguingly, the angular distributions of the excited product pairs(61, 0)s, (11, 0)s, and (31, 0)sare remarkably similar and comprise the traits of both the peripheral mechanism and resonance pathway. Possible interpretation and implication are suggested. In addition, due to the spectral overlap of the REMPI bands and heavily congested image features, a robust data analysis method is developed, which enables us to extract the dynamics attributes of a weak feature buried in the proximate, more intense ones with high fidelity.

Stretching-mode specificity in the Cl + CH3D(v1-I, v1-II, and v4 = 1; |jK〉) reactions: dependency on the initial |jK〉 selectivity

“…At E c = 10 kcal mol À1 all three CH 3 -stretching excitations of reagents promoted the reactivity in forming a major product pair of (v CH 2 D , v HCl ) s = (0 0 , 0/1) s with a prominent mode-propensity of v 4 4 v 1 -I 4 v 1 -II. 3 The vibrationally excited CH 2 D product pairs of (6 1 , 0) s , (1 1 , 0) s , and (3 1 , 0) s appeared to be minor channels and displayed a reverse propensity of v 4 o v 1 -I E v 1 -II for (6 1 , 0) s , while v 4 4 v 1 -I for (1 1 , 0) s . From the observed angular distributions, we conjectured that irrespective of the initial mode of excitation, the (0 0 , 0) s product pair proceeds by a direct abstraction of the peripheral type, whereas the (0 0 , 1) s pair is mediated via a resonance pathway.…”

“…Over the past few years, our laboratory at IAMS has carried out an extensive study on the effects of the CH 3 -stretching excitations of CH 3 D(v i = 1) in reactions with the Cl-atom. [1][2][3][4] The choice of the Cl + CH 3 D(v i ) reaction for such comprehensive investigations is because it offers the opportunity to address several fundamentally important aspects of polyatomic reactivity in general. [1][2][3][4][5][6][7][8][9][10] From the reagent side, there are three different CH 3 -stretches (v i ): the degenerate mode of asymmetric stretch (v 4 ) and a pair of Fermi-coupled symmetric-stretch/ overtone-bend states (v 1 -I and v 1 -II).…”

“…[1][2][3][4] The choice of the Cl + CH 3 D(v i ) reaction for such comprehensive investigations is because it offers the opportunity to address several fundamentally important aspects of polyatomic reactivity in general. [1][2][3][4][5][6][7][8][9][10] From the reagent side, there are three different CH 3 -stretches (v i ): the degenerate mode of asymmetric stretch (v 4 ) and a pair of Fermi-coupled symmetric-stretch/ overtone-bend states (v 1 -I and v 1 -II). 7,11 Hence, one can address not only the impacts of vibrational-mode specificity on chemical reactivity (v 4 versus v 1 ), 7 but also the possible influence of the quantum mechanical (Fermi) phase on the different reactivities between the v 1 -I and v 1 -II reagents.…”

“…This is in sharp contrast to the dual mechanisms, as just mentioned, of the other vibrationally excited pairs of (1 1 , 0) s , (3 1 , 0) s , and (6 1 , 0) s in the same CH 2 D + HCl isotopic channel. 3 More recently, two of us reported an in-depth study on the reactivity effect of the Fermi phase by focusing on the relative ICS of the CH 2 D(0 0 /6 1 ) + HCl(v) channels in the reactions with v 1 -I and v 1 -II of CH 3 D(v i ) with the Cl-atom over the E c range of 2.5-10 kcal mol À1 . 1 Based on a generic collisional model, a decisive metric was proposed that enabled us to prove that the Fermi phase indeed exerted a profound impact-far beyond the conventional reactivity-borrowing framework 17,18 -on the chemical reactivity in the formation of the CH 2 D(0 0 ) + HCl(v = 0, 1) channels, but intriguingly the same could not be said for the CH 2 D(6 1 ) + HCl(v = 0) channel.…”

“…Crucially, all studies outlined above employed the same single rotational state of |jKi = |10i for the vibrationally excited reagents CH 3 D(v 4 , v 1 -I, and v 1 -II). [1][2][3][4] As such, the reactivity comparison among different stretch-excited reactions could be free of (or at least with minimal) rotational-mode effects. Nonetheless, previous studies on the two analogous reactions of Cl + CHD 3 (v 1 = 1, |jKi) and CH 4 (v 3 = 1, |jNli) did reveal prominent, perplexing rotational-mode impacts on both ICS and DCS.…”