Proton transfer dynamics in the hydrogen bond: a direct measurement of the incoherent tunnelling rate by NMR and the quantum-to-classical transition

Brougham, Dermot F.; Horsewill, A.J.; Jenkinson, R. I.

doi:10.1016/s0009-2614(97)00493-4

Cited by 72 publications

(97 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Extra polated to zero pressure, the rate of incoherent tunnelling agrees with the values obtained with the optical spectroscopic techniques and by novel NMR methods [9]. At high temperature, the classical limit (barrier hopping) is asymptotically approached.…”

Section: Fig 3 Three Diagrams Abovesupporting

confidence: 81%

“…At higher temperatures, the proton correlation time, τc, defined by 1/τc = kL R +kR L , was determined from NMR and QENS [4][5][6][7][8][9]. Of particular interest is the temperature region in which other thermally activated processes begin to contribute to the proton transfer and mark the onset of the transition from pure quantum mechanical to classical barrier crossing.…”

Section: Figmentioning

confidence: 99%

See 1 more Smart Citation

Proton Tunnelling in Intermolecular Hydrogen Bonds

1997

View full text Add to dashboard Cite

Section: Fig 3 Three Diagrams Abovesupporting

confidence: 81%

Section: Figmentioning

confidence: 99%

Proton Tunnelling in Intermolecular Hydrogen Bonds

1997

View full text Add to dashboard Cite

“…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

View full text Add to dashboard Cite

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.

show abstract

“…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

View full text Add to dashboard Cite

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...

show abstract

Proton transfer dynamics in the hydrogen bond: a direct measurement of the incoherent tunnelling rate by NMR and the quantum-to-classical transition

Cited by 72 publications

References 11 publications

Proton Tunnelling in Intermolecular Hydrogen Bonds

Proton Tunnelling in Intermolecular Hydrogen Bonds

Environment-induced dephasing versus von Neumann measurements in proton tunneling

Multiple Proton Transfer: From Stepwise to Concerted

Contact Info

Product

Resources

About