The dynamics of hydrogens in double well potentials: The transition of the jump rate from the low temperature quantum-mechanical to the high temperature activated regime

Heuer, Andreas; Haeberlen, Ulrich

doi:10.1063/1.461795

Cited by 100 publications

(70 citation statements)

References 37 publications

(4 reference statements)

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“…Although there have also been some critical discussions about the hydrogen transfer rate 1 as a function of temperature, 5,6,11 we used the simple equation for Table 1.…”

Section: Resultsmentioning

confidence: 99%

“…11 The transfer of deuteron was also investigated by 2 H NMR relaxation. 6 The transfer rate does not follow a simple Arrhenius law and a tunneling effect dominates the transfer motion in the Ł Correspondence to: S. Takeda low-temperature region for both isotopes. The isotope effect of the transfer rate was found in all temperature regions and was particularly large at low temperatures.…”

Section: Introductionmentioning

confidence: 99%

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An indication of slowing down of hydrogen atom transfer in isotopically mixed hydrogen bonds of benzoic acid crystals

Takeda

Tsuzumitani

2001

Magn. Reson. Chem.

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Benzoic acid molecules form a dimeric unit of carboxyl groups in the crystalline phase and two acid protons form a pair. In the case of a proton/deuteron mixed hydrogen-bond system, proton-deuteron pairs (HD pairs) as dimers may exist in a stochastic distribution probability depending on the mole fraction of deuteron. Transfer rates of proton and deuteron in the HD pairs were investigated by spin-lattice relaxation rate T

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“…Although there have also been some critical discussions about the hydrogen transfer rate 1 as a function of temperature, 5,6,11 we used the simple equation for Table 1.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An indication of slowing down of hydrogen atom transfer in isotopically mixed hydrogen bonds of benzoic acid crystals

Takeda

Tsuzumitani

2001

Magn. Reson. Chem.

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“…A well-studied example of proton tunneling in chemistry has been the double-H-bonded benzoic acid dimer [3][4][5][6][7][8][9][10][11][12][13], * a.godbeer@surrey.ac.uk † j.al-khalili@surrey.ac.uk ‡ p.stevenson@surrey.ac.uk making this simple structure useful for modeling more complex chemical and biological systems that may involve proton tunneling. The first experimental evidence for proton tunneling in biological systems came in fact from the study of enzyme catalysis in 1989 (for the enzyme alcohol dehydrogenase, which transfers a proton from an alcohol molecule to a molecule of nicotinamide adenine dinucleotide), where the effects of atomic mass on reaction rates through isotopic substitution revealed clear evidence of quantum tunneling even at relatively high temperatures [14].…”

Section: Introductionmentioning

confidence: 99%

Environment-induced dephasing versus von Neumann measurements in proton tunneling

2014

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In this work we compare two theoretical approaches to modeling the action of the environment on an open quantum system. It is often assumed that as the temperature of the environment surrounding a quantum system increases, so does the speed of environment-induced dephasing, or decoherence (dynamical noise), and so the efficacy of processes such as quantum tunneling drops. An alternative way of viewing the action of the environment is to consider it as carrying out von Neumann-type measurements that, in the limit of continuous observation, lead to the so-called quantum Zeno effect, whereby the system is never allowed to evolve because its wave function is collapsed to its initial state with overwhelming likelihood. However, it has been established in recent years that under certain conditions quantum processes such as tunneling can actually be enhanced (thermally assisted) when the system couples to its environment, as this allows transitions to higher-energy eigenstates closer to the top of the potential barrier. Here we show that, over a specific temperature range, increasing the temperature of the heat bath to encourage such thermally induced tunneling is equivalent to increasing the frequency of a von Neumann-type measurement on the system by the environment (an anti-Zeno effect). However, this correspondence between these two independent pictures of quantum measurement breaks down above a certain limit: Increasing the frequency of measurement above this limit leads to a reversal from an anti-Zeno to a Zeno effect and the tunneling rate decreases again, whereas raising the temperature further leads to a leveling off in the tunneling probability.

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“…Recently these measurements were extended to crystals in which all or part of the benzoic acid molecules carry a mobile deuteron instead of a mobile proton. In this way it was possible to measure rate constants as a function of temperature not only for HH but also for HD and DD transfer [49][50][51]. The resulting Arrhenius plots, illustrated in Fig.…”

Section: Other Dimeric Systemsmentioning

confidence: 99%

Multiple Proton Transfer: From Stepwise to Concerted

Smedarchina

Siebrand

Fernández‐Ramos

2006

Hydrogen‐Transfer Reactions

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It is well recognized that reactions involving the transfer of a proton or hydrogen atom are special in that these particles can tunnel through classically forbidden regions [1]. The wave-like properties also add a new element to reactions in which two or more protons transfer, since under appropriate conditions, they may allow the protons to move as a single particle. In this contribution we review the dynamics of such reactions [2], focusing on double proton transfer for simplicity. In particular, we probe how the motion of one proton influences that of the other and which conditions lead to weak or strong correlation between their motions. Generally speaking, no correlation results in independent transfer and weak correlation in stepwise transfer. Strengthening the correlation will ultimately lead to concerted transfer and may give rise to synchronous transfer if the transferred particles are equivalent.While proton-proton correlation is a unifying concept that allows us to classify and understand the various multiproton transfer mechanisms, it is not a quantity that is easily measured or calculated. In dealing with a specific reaction, one tends to use a simpler approach based on the search for a transition state, i.e. a configuration along the transfer path characterized by a first-order saddle point representing a vibrational force field with one imaginary frequency. More generally, the presence of two mobile particles implies that the potential energy surface contains stationary states with zero, one, or two imaginary frequencies, representing, respectively, a stable intermediate, a transition state, and a state with a secondorder saddle point.A stable intermediate roughly halfway along the trajectory implies barriers separating it from the equilibrium configurations. Such a potential favors stepwise transfer under conditions where the intermediate is thermally accessible. This basically reduces the dynamics to that appropriate for single proton transfer, but leaves open the question of how to deal with transfer at low temperature. A barrier corresponding to a single transition state, similar to that observed for single proton transfer, implies concerted transfer of the two protons. This again can Hydrogen-Transfer Reactions. Edited by be treated by the methods developed for single proton dynamics [1,3]. However, if, instead, this barrier corresponds to a second-order saddle point, it represents concerted motion along two proton coordinates. This situation does not immediately reveal the nature of the corresponding transfer process, but it drives home the point that the presence of two mobile protons allows at least two transfer mechanisms. On a potential energy surface with more than one saddle point, there will in general be multiple pathways along which the potential has a doubleminimum profile. To analyze the transfer dynamics governed by such a potential, we need an approach that goes beyond the question whether the transfer is concerted or stepwise.To elucidate the effect of proton-proton correlation...

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The dynamics of hydrogens in double well potentials: The transition of the jump rate from the low temperature quantum-mechanical to the high temperature activated regime

Cited by 100 publications

References 37 publications

An indication of slowing down of hydrogen atom transfer in isotopically mixed hydrogen bonds of benzoic acid crystals

An indication of slowing down of hydrogen atom transfer in isotopically mixed hydrogen bonds of benzoic acid crystals

Environment-induced dephasing versus von Neumann measurements in proton tunneling

Multiple Proton Transfer: From Stepwise to Concerted

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