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Pan H, Liu K. State-to-State Dynamics in Mode-Specific Reactions of Cl + CH 3D( v1-I, v1-II, and v4 = 1; |10⟩): Loss of Memory or Not. J Phys Chem Lett 2023; 14:1769-1776. [PMID: 36762846 DOI: 10.1021/acs.jpclett.3c00133] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Several decades of the study of reaction dynamics culminate in the concept of mode specificity and bond selectivity in polyatomic systems. Until very recently, the main concern of those studies has been total reactivity and little attention has been paid to the mode-specific effects on the more detailed product-state and angular distributions. Conventional wisdom would anticipate that the fine detail should reveal a more pronounced mode dependency. However, a few recent studies showed that the product distributions could appear to be surprisingly insensitive to the modes of internal excitation of reagents. This counterintuitive finding led to a concept of loss of memory. Here, we present detailed experimental results in the reactions of the Cl atom with three distinct stretching-excited CH3D(vCH3 = 1) reagents. In conjunction with the previous reports on various aspects of this reaction, such a comprehensive set of data enables us to perform an in-depth examination of the validity of this new concept.
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Affiliation(s)
- Huilin Pan
- Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, P. R. China
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan 10617
| | - Kopin Liu
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan 10617
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- Aerosol Science Research Center, National Sun Yat-sen University, Kaohsiung, Taiwan 80424
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Mondal S, Pan H, Liu K. Stretching-mode specificity in the Cl + CH 3D( v1-I, v1-II, and v4 = 1; | jK〉) reactions: dependency on the initial | jK〉 selectivity. Phys Chem Chem Phys 2022; 24:24050-24061. [PMID: 36168830 DOI: 10.1039/d2cp03614b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The title reactions were studied at a collisional energy of 5.4 kcal mol-1 in a crossed-beam product-imaging experiment. The dynamics attributes of the dominant ground-state CH2D(00) and the accompanied C-D bend-excited CH2D(61) products were imaged in reactions with totally 16 ro-vibrationally selected states of the CH3D(vi, |jK〉) reagents. We found that all three vibrational excitations yielded marked |jK〉-dependent rate-enhancements in forming the (00, 0/1)s product pairs. Furthermore, for a given rotational |jK〉-mode, a vibrational-mode propensity of v4 > v1-I > v1-II in rate promotion and a clear manifestation of the Fermi-phase-induced interference effect of the latter two were observed. Compared to the reactivity of the rotationless state |jK〉 = |00〉, a minute rotational-excitation of all three stretch-excited CH3D(vi = 1) reagents could yield significantly higher reaction rates for the product pair (00, 0)s, but not so for (00, 1)s. The signals in forming the (61, 0)s pair were clearly notable but smaller than that of the ground-state reaction product pair, (00, 0)g. An opposite propensity of v1-II ≈ v1-I > v4 with a milder dependency on the initial |jK〉-states was observed. The angular distributions of the (00, 0)s pairs were nearly identical for all ro-vibrationally excited reagents, displaying the typical trait for a direct abstraction of the rebound mechanism. Similar distributions were found for the (61, 0)s pairs; yet, both pairs deviated substantially from the peripheral feature of the ground-state reaction pair of (00, 0)g. Those of the (00, 1)s pairs in reactions with v4-excitation featured a prominent forward-peaking distribution-suggestive of a time-delayed, resonance-mediated pathway, again with little dependency on the initial |jK〉-states. As for the reactions with the two Fermi-dyads, v1-I and v1-II, albeit showing globally similar distributions to that for v4, a substantial variation with the initial rotational-mode excitation could be discerned in the forward-peaking features. To unravel the impact of the Fermi-phase on the |jK〉-dependent attributes, we adopted a comparative approach by contrasting the observations in reactions with the Fermi-dyad reagents (the superposition states) to those with the pure-state reagents. Remarkable distinctions are unveiled and elucidated with the unexplained results explicitly pointed out, which call for future theoretical investigations for deeper understanding.
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Affiliation(s)
- Sohidul Mondal
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, P. O. Box 23-166, Taipei, 10699, Taiwan.
| | - Huilin Pan
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, P. O. Box 23-166, Taipei, 10699, Taiwan. .,Department of Chemistry, Southern University of Science and Technology, Shenzhen, 518055, P. R. China
| | - Kopin Liu
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, P. O. Box 23-166, Taipei, 10699, Taiwan. .,Aerosol Science Research Center, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan.,State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian, 116023, P. R. China
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Mondal S, Liu K. Imaging the Mode-Specificity in Cl + CH 3D( v1-I, v1-II, v4 = 1; | jK⟩ = |10⟩) → CH 2D(4 1) + HCl( v). J Phys Chem A 2022; 126:2825-2831. [PMID: 35499972 DOI: 10.1021/acs.jpca.2c01852] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a crossed-beam imaging experiment on the title reactions at two collisional energies (Ec) of 5.3 and 10 kcal mol-1. Both the integral cross sections relative to the ground-state reactivity and the differential cross sections were measured and compared. We found that one-quantum excitations of the CH3-stretching vibrations of the CH3D reagent exerted profound mode-specificity in forming the umbrella-mode-excited CH2D(41) products with the vibrational efficacy of v4 > v1-I > v1-II at both Ec values. The concomitantly formed HCl(v) coproducts were vibrationally cold. Interestingly, the branching ratios of (v = 1)/(v = 0) appeared invariant to the initial stretch-modes of excitation at Ec = 5.3 kcal mol-1, yet exhibited a pronounced mode-specific dependency in the order of v1-II > v1-I > v4 at Ec = 10.3 kcal mol-1. This large and Ec-dependent disparity between the two Fermi-coupled reagents, v1-I and v1-II, is particularly significant and could be another facet─in addition to that in the recently reported vibrational enhancement factors─of the Fermi-phase-induced interference effect manifested in the product vibrational branching ratio. The pair-correlated angular distributions (vCH2D, vHCl)s = (41, 0)s in the three stretch-excited reactions were globally alike and resembled that of the ground-state reaction pair (00, 0)g, suggestive of a direct abstraction mechanism of the peripheral type. This is in sharp contrast to all other vibrationally excited pairs of (11, 0)s, (31, 0)s, and (61, 0)s previously reported in the CH2D + HCl isotopic channel, for which both the direct abstraction and a time-delayed resonance pathway partake.
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Affiliation(s)
- Sohidul Mondal
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, 10617, Taiwan
| | - Kopin Liu
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, 10617, Taiwan.,Aerosol Science Research Center, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan.,State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian, 116023, P. R. China
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Fermi-phase-induced interference in the reaction between Cl and vibrationally excited CH 3D. Nat Chem 2022; 14:545-549. [PMID: 35361912 DOI: 10.1038/s41557-022-00914-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 02/18/2022] [Indexed: 11/08/2022]
Abstract
Mode selectivity is a well-established concept in chemical dynamics. A polyatomic molecule possesses multiple vibrational modes and the mechanical couplings between them can result in complicated anharmonic motions that defy a simple oscillatory description. A prototypical example of this is Fermi-coupled vibration, in which an energy-split eigenstate executes coherent nuclear motion that is comprised of the constituent normal modes with distinctive phases. Will this vibrational phase affect chemical reactivity? How can this phase effect be disentangled from more classical amplitude effects? Here, to address these questions, we study the reaction of Cl with a pair of Fermi states of CH3D(v1-I and v1-II). We find that the reactivity ratio of (v1-I)/(v1-II) in forming the CH2D(v = 0) + HCl(v) products deviates significantly from that permitted by the conventional reactivity-borrowing framework. Based on a proposed metric, this discrepancy can only be explained when the scattering interferences mediated by the CH3D vibrational phases are explicitly considered, which expands the concept of vibrational control of chemical reactivity into the quantum regime.
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A Ten-Dimensional Quantum Dynamics Study of the H+CH 3D→H 2+CH 2D Reaction. CHINESE J CHEM PHYS 2022. [DOI: 10.1063/1674-0068/cjcp2112284] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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