“Inverted” CO molecules on NaCl(100): a quantum mechanical study

Sinha, Shreya; Saalfrank, Peter

doi:10.1039/d0cp05198e

Cited by 5 publications

(19 citation statements)

References 35 publications

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“…Remarkably, experiments reveal well‐resolved line spectra. This problem has already drawn interest from theorists developing PESs 491,492 applying quantum dynamical methods 493 . The challenges are formidable, but this system offers a proving ground for testing quantum dynamical methods in the high dimensions of condensed phases, providing a blueprint for exciting experimental and theoretical advances that may lead to fascinating discoveries, and take us systematically toward the dream of predicting and watching the intricate motions of individual atoms during a catalytic reaction.…”

Section: Discussionmentioning

confidence: 99%

Chemical dynamics from the gas‐phase to surfaces

2021

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The field of gas‐phase chemical dynamics has developed superb experimental methods to probe the detailed outcome of gas‐phase chemical reactions. These experiments inspired and benchmarked first principles dynamics simulations giving access to an atomic scale picture of the motions that underlie these reactions. This fruitful interplay of experiment and theory is the essence of a dynamical approach perfected on gas‐phase reactions, the culmination of which is a standard model of chemical reactivity involving classical trajectories or quantum wave packets moving on a Born–Oppenheimer potential energy surface. Extending the dynamical approach to chemical reactions at surfaces presents challenges of complexity not found in gas‐phase study as reactive processes often involve multiple steps, such as inelastic molecule‐surface scattering and dissipation, leading to adsorption and subsequent thermal desorption and or bond breaking and making. This paper reviews progress toward understanding the elementary processes involved in surface chemistry using the dynamical approach. Key points The fruitful interplay between chemistry and physics leads to an atomic scale view of reactions taking places at catalytically active surfaces. Improved observations of chemical reactions taking place in complex environments drive the development of new approaches to theoretical chemistry. Complex reaction networks from real catalysts are boiled down to their elementary steps and examined from first principles.

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Section: Discussionmentioning

confidence: 99%

Chemical dynamics from the gas‐phase to surfaces

2021

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“…When CO adsorbs at a NaCl(100) surface 15 – 17 , it may bind with the C atom or the O atom facing the surface, resulting in distinct vibrational signatures for the two orientations 3 , 18 . Subsequent work on the potential energy surface for this system 19 found the O-bound isomer lying approximately 610 cm −1 higher in energy than the more stable C-bound isomer, with an approximately 570 cm −1 barrier for O-bound → C-bound isomerization 4 . Calculation of the two-dimensional (CO rotation θ , translation from surface Z ) wavefunctions residing in the double-well system yielded thousands of vibrational states; those lying below the barrier height are predominantly localized in either the C-bound or O-bound well, providing the basis for a first-principles quantum theory of state-to-state isomerization rates.…”

Section: Mainmentioning

confidence: 92%

“…2b provide the first suggestion that these rate constants reflect a tunnelling process, as all three values are substantially lower than the expected barrier height of 574 cm −1 (ref. 4 ). The tunnelling hypothesis is further supported by comparison to expectations for an over-the-barrier process, which can be done using transition state theory (TST).…”

Section: Arrhenius Parameters Indicate Tunnellingmentioning

confidence: 99%

“…10 ). Here we solve the time-independent Schrödinger equation to obtain all vibrational eigenstates up to the classical isomerization barrier for each isotopologue, using the previously reported potential energy surface 4 . These states define a two-dimensional ‘system’ in perturbative contact with a ‘bath’ of phonon states, produced by low-frequency motions of the CO monolayer and the NaCl solid.…”

Section: Quantum Rate Theory For Isomerizationmentioning

confidence: 99%

“…In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface 3 , 4 , showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment.…”

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confidence: 99%

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Condensed-phase isomerization through tunnelling gateways

Choudhury

DeVine

Sinha

et al. 2022

Nature

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We observe that the orientational isomerization of CO on a NaCl(100) surface proceeds by thermally-activated tunneling between 19 and 24K. The rate constants of three isotopomers follow an Arrhenius temperature dependence, exhibiting activation energies below the reaction's predicted barrier height and anomalously small prefactors. In addition, the rates depend strongly on isotope, but non-intuitively on mass. A quantum rate theory of condensedphase tunneling qualitatively explains these observations. Vibrationally excited states, accidentally close in energy but localized on opposite sides of the isomerization barrier, provide tunneling gateways between the isomers in a process that can be many orders-of-magnitude faster than rates predicted by commonly used semi-classical models. This suggests heavy-atom condensed-phase tunneling may be more important than currently assumed.

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Manipulating tunnelling gateways in condensed phase isomerization

et al. 2023

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When a chemical reaction occurs via tunnelling, a simple mass‐dependence is expected, where substitution of atoms by heavier isotopes leads to a reduced reaction rate. However, as shown in a recent study of CO orientational isomerization at the NaCl(1 0 0) interface, the lightest isotopologues need not exhibit the fastest tunnelling; for the CO/NaCl system, the non‐monotonic mass‐dependence is understood through a new picture of condensed phase tunnelling where the overall rate is dominated by a few pairs of reactant/product states. These state‐pairs – termed quantum gateways – gain dynamical importance through accidentally enhanced tunnelling probabilities, facilitated by a confluence of the energetic landscape underlying the reaction as well as the phonon bath of the surrounding medium. Here, we explore gateway tunnelling through measurements of the kinetic isotope effect for CO isomerization in a monolayer buried by many layers of either CO or N2. With an N2 overlayer, tunnelling rates are accelerated for all four isotopologues (12C16O, 13C16O, 12C18O and 13C18O), but the degree of acceleration is isotopologue‐specific and non‐intuitively mass dependent. A one‐dimensional tunnelling model involving an Eckart barrier cannot capture this behaviour. This reflects how a modification of the potential energy surface moves states in and out of resonance, thereby changing which tunnelling gateways can be accessed in the isomerization reaction. Key points The paper describes new systems that showcase resonance‐enhanced condensed phase tunnelling. Condensed phase tunnelling as described in this work may have implications for astrochemistry. A previously hypothesized mechanism is subjected to subsequent experimental scrutiny – the hypothesis stands the test.

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“Inverted” CO molecules on NaCl(100): a quantum mechanical study

Abstract: Inverted (“O-down”) CO adsorbates on NaCl(100), recently observed experimentally after IR vibrational excitation (Lau et al., Science, 2020, 367, 175–178), are characterized using periodic DFT and a quantum mechanical description of vibrations.

Cited by 5 publications

References 35 publications

Chemical dynamics from the gas‐phase to surfaces

Chemical dynamics from the gas‐phase to surfaces

Condensed-phase isomerization through tunnelling gateways

Manipulating tunnelling gateways in condensed phase isomerization

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