Comment on ‘Lifetime broadening in angle-resolved photoemission’ by A.B. McLean,C.E.J. Mitchell and I.G. Hill

In a recent letter [A.B. McLean, C.E.J. Mitchell and I.G. Hill, Surf. Sci. 314 (1994) L925] it was suggested that life-time broadening alone could explain why surface state photoemission line-widths have been observed to increase as the initial states approach the Fermi level. I wish to point out that the used model is unphysical, that the agreement with experimental data is quite fortuitous, and that the experimental observations are satisfactorily understood in terms of established models.     

Comment on ‘activated chemisorption of methane and tunneling: A second look’ by T.C. Lo and G. Ehrlich

We have previously reanalyzed the data of Lo and Ehrlich on the activated chemisorption of CH₄ and CD₄ on W(211) in terms of a tunneling model. In the Letter cited above, Lo and Ehrlich criticize the tunneling model due to an insensitivity of the model with respect to the mass of the heavier isotope. In this Comment we show why the mass insensitivity is a natural consequence of the smaller tunneling probability for the deuterium isotope, and not a breakdown in the model.     

Comment on ‘structure of α-Fe2O3 single crystal surfaces following Ar+ ion bombardment and annealing in O2’ by R.J. Lad and V.E. Henrich

A recent paper by Lad and Henrich [Surface Sci. 193 (1988) 81], on the phase changes induced by Ar⁺ bombardment and annealing in O₂ at Fe₂O₃ single crystal surfaces, is commented upon. It is pointed out that quantitative XPS analysis would have provided more direct information on phase changes induced by surface treatments. It is suggested that chemical effects contribute to the O 1s spectrum asymmetry observed in Ar⁺ bombarded Fe₂O₃ surfaces.     

Comment on ‘equilibrium of segregation in Ag/Cu(111): kinetics and isotherms by J. Eugène,B. Aufray and F. Cabané’

It is shown in this comment that the equilibrium isotherm calculated in a recent paper by J. Eugène et al. [Surf. Sci. 241 (1991) 1] from the segregation curve is incorrect with regard to both the basic assumptions and the numerical integration procedure.     

Quantum tunneling and the activated chemisorption of methane on tungsten: Comment on ‘activated chemisorption of methane and tunneling’ by T.-C. Lo and G. Ehrlich

Results of recent experimental studies on the dissociative chemisorption of CH₄ and CD₄ on W(211) were previously concluded to be inconsistent with earlier proposed quantum tunneling models. In this Letter we re-analyze the experimental results and show them to be entirely consistent with a tunneling mechanism. We also show that the reported inconsistency arises from the use of an oversimplified model for the tunneling transmission coefficient.     

Response to Comment on ‘Non-representative Quantum Mechanical Weak Values’ by Ben-Israel and Vaidman

Ben-Israel and Vaidman (Found Phys 47:467–470, 2017) have raised objections to my arguments that there are cases where a quantum mechanical weak value can be said not to represent the system to which it pertains. They are correct in pointing out that some of my conclusions were too general. However, for weak values of projection operators my conclusions still stand.     

Comment on ‘Time-dependent paths,fictive temperatures and residual entropy of glass’

In their recent paper, Johari and Aji claim that there is a positive residual entropy of a glass. Here we show that their arguments in support of this view are incorrect.     

Comment on “The growth of Fe overlayers on Ag(100)” by G.C. Smith,H.A. Padmore and C. Norris

Smith, Padmore and Norris have claimed that the first three monolayers of Fe grown at room temperature on Ag(100) form a strained fcc γ-Fe layer for which the mismatch to the substrate is 11%. We point out a simple error in their calculations of mismatch, and suggest instead that such growth produces a bcc α-Fe(100) film, for which the mismatch to the substrate is only 0.8%.     

Reply to “Comment on ‘Lifetime broadening in angle-resolved photoemission’ by H.I. Starnberg”

The physical origin of line broadening in angle-resolved photoemission is reexamined in the light of new experimental results and a recent critique of the Fraxedas model of lifetime broadening.     

Comment on ‘Cr LVV Auger emission and photoreduction of hexavalent Cr oxides by A.G. Schrott,G.S. Frankel,A.J. Davenport,H.S. Isaacs,C.V. Jahnes and M.A. Russak’

A paper by Schrott et al. [Surf. Sci. 250 (1991) 139] on the Auger Cr LVV spectra of Al/Cr alloys is commented on.The area of major disagreement regards the hypothesis that Al-alloying suppresses the Cr LVV decay. It is pointed out that the surface chemical composition of the alloys should be considered in detail, and that instrumental factors and the presence of surface contamination would account for the negligible Cr LVV intensity.     

Dynamics on reactive potential energy surfaces: hyperspherical view and signatures of ‘quantum chaos’

Adiabatic energy levels for two prototypical reactions, F + H₂ → HF + H and He + H⁺ ₂ → HeH⁺ + H, are analysed by means of statistical tests. These levels result from quantum mechanical calculations of dynamics based on the hyperspherical approach, and are given as a function of the total inertia of the system measured by the hyperradius ρ The nearest neighbour level spacing distributions of Brody and of Berry and Robnik, the spectral rigidity δ₃ of Dyson and Mehta and the correlation coefficient are reported, together with other properties, such as variance, skewness and kurtosis of the distributions. Trends are studied as a function of ρ, proposed as a natural control variable. For low ρ, which correspond to the transition state, evidence is found of Wigner-like behaviour, which is interpreted as the signature of quantum chaos. On the passage of the systems through intermediate ρ a mixture of Wigner- and Poisson-like behaviour emerges. The situation for high ρ where reactants and products of the reactions are well separated, is characterized by a tendency towards regular Poisson-like behaviour. A comparison between the two investigated systems shows that the chaotic regime in the transition state region is more pronounced for the He reaction, which proceeds through a deep well and whose dynamics are characterized by a rich resonance pattern.