Electron-Induced Chemistry in the Condensed Phase
Round 1
Reviewer 1 Report
The author presented some challenges that one faces in studies of electron-induced chemistry in the condensed phase. He pointed out the differences that exist in electron interactions within gas phase and condensed phase and identified three main demanding questions that need to be addressed during such studies. These examples have been given and the conclusions have been derived. The author rightly stressed out that there are very little data on the fragmentation pathways or energy dependence of ND processes, while DEA processes are extensively studied in gas phase, what is helping in predictions which reaction channels are possibly open in condensed-phase chemistry. This paper on condensed-phase chemistry triggered by electron-molecules interactions is excellently written study and overview, in outstanding English vocabulary, so it should be published as it is.
Author Response
Thank you very much for your kind appraisal.
After some minor changes to the text suggested by the other reviewers and a major overhaul of the Figures, I feel the paper is even better now.
Thank you for your time!
Reviewer 2 Report
In general, the manuscript was well written and highlights a number of importance issues in understanding condensed phase chemistry using gas-phase cross section data. I personally would have been a bit more positive about the state of the experimental data due to the fact that the gas-phase experiments are difficult especially when detailed information is required. That said, I believe this is a good contribution to the literature.
A few general comments on formatting.
The subscripts and superscripts were not well placed, but this is a font issue.
The figure captions should not cover the threshold region of the calculations.
Errorbars on the experimental data points would help.
I have listed my suggested corrections and/or changes below.
Line 12: remove 'new'
Line 14: These shifts are due to multi-body processes.
Line 30: Is there a more current reference than [1].
Line 30-31: In principle, these electrons share some of the incident energy. While this statement is true, it does ignore the fact that the electrons all make it to a few eV at the end of their track because they too much energy to recombined.
Line 32: List the 'three main principle processes'
Line 65: Typo - (D)EA
Line 79: ... potential, IE, of ...
Line 80: NIST Chemistry Webbook
Line 84: remove 'these two,'
Line 88: Could you provide a reference, in particular for the energy dependence?
Line 90: There are intermediate paths which makes this statement confusing, at first.
Line 94: The energy width of the electron beam from the flood gun used is 0.5-1 eV. The tail of this distribution could easily extend to a few eV. It is unclear from the text if the a realistic electron beam width was considered as the calculations do not appear to be convolved.
Line 96: Are there data points missing in Figure 1?
Line 109: ... by the polarization ...
Line 116: typo - EA should be DEA
Line 118: There are many more results for more complex molecules such as DNA and RNA basis and similar.
Line 118: Should caveats be caveat?
Line 118: 'apply: The ...' should be 'apply: the ...'
Line 128: Missing comma after 'like'.
Line 129: Missing full stop at the end of the equation.
Line 132: Should reference 14 be listed at the end of the sentence?
Line 146: Rawat et al. [14] ?
Line 150: Figure 3 is readable, but did not render well in my copy.
Line 155: Consider rewriting this sentence. You've just used the DEA cross section to explain one process followed by pointing where it has not helped, so perhaps it would be better to state that is not 'reliable' rather than 'good'.
Line 159: Comma after 'ethanol'.
Line 160: Comma after equation
Line 162: Replace 'just' with 'only'
Line 177: Slightly confused here. H2O- can only produce C2H4 radical in collisions with C2H4.
Line 187: 'endeavoring to investigate ...'
Line 193-194: Comment - The definition of the total scatter cross section does not include information on branching ratios. It only tells you the rate at which the sum of all processes occurs for an isolated target. Additionally, it is not differential in angular or energy-sharing, which is of the utmost importance in following the chemical pathways present in the condensed phase.
Line 197: Comment - You could be a bit more optimistic. The fact that any absolute DEA cross sections are available is a good thing as the experiments are difficult. In particular, you have used them to highlight the current "conundrum", which is also a good thing.
Author Response
First of all let me thank you for your thorough review!
I have incorporated all the changes you suggested, except for a few, namely:
Line 30: Is there a more current reference than [1].
No, there seems to be no newer estimate. Everyone keeps citing this number. It is either well-established fact, or well-established folklore.
Line 30-31: In principle, these electrons share some of the incident energy. While this statement is true, it does ignore the fact that the electrons all make it to a few eV at the end of their track because they too much energy to recombined.
In the case of the experiments portrayed here, the films are much too thin to stop an electron completely. But even if it could, the argument that for every one primary electron you get many thousands of slow electrons still stands.
Line 32: List the 'three main principle processes'
The listing follows in the next paragraph. I have tried to made this more clear by using ':' at the end of the sentence.
Line 88: Could you provide a reference, in particular for the energy dependence?
below IE + bond dissociation energy, no fragmentation CAN occur. This can be seen from the appearance energies for fragment ions, which can be found in databases.
Line 90: There are intermediate paths which makes this statement confusing, at first.
I have changed the wording to "net reaction" to make this less confusing
Line 94: The energy width of the electron beam from the flood gun used is 0.5-1 eV. The tail of this distribution could easily extend to a few eV. It is unclear from the text if the a realistic electron beam width was considered as the calculations do not appear to be convolved
The energy width is not considered here, as it smaller than the energy distance between individual measurements. In other experiments, we have observed very sharp resonances that occur at 4 eV, but neither at 3 nor 5 eV. The energy width given by the manufacturer seems to be a worst case estimate for very high energies, and not FWHM at 5 - 15 eV.
Line 96: Are there data points missing in Figure 1?
No, the data is taken from Böhler et al., as is. The authors also did not publish error bars for their data, so Figure 1 has one error bars.
Line 150: Figure 3 is readable, but did not render well in my copy.
There seems to be little I can do about that. It is a vector graphic, so it should be rendered in sufficient resolution in the final print.
Line 177: Slightly confused here. H2O- can only produce C2H4 radical in collisions with C2H4.
The process is not triggered by EA to water. The text has been amended to make this clearer.
Reviewer 3 Report
The article “Electron-induced chemistry in the condensed phase” by J. H. Bredehöft discusses low-energy electron-induced chemistry in the condensed phase, the relevance of the gas phase data in the investigation of such effects and stress important differences in the case of electron-induced processes studied in a condensed phase relative to the gas phase. This is a very nice article that briefly but entirely underlines the facts that should be well-known but indeed are so often unknown both in the gas phase and condensed phase research communities.
Although the article is rather of an educational character and presents experimental results already published previously, the discussion and presentation of the results make the paper still interesting and useful as a publication in this field of research.
Therefore, I recommend this article for publication in the journal Atoms.
There are, however, a few comments that I think the author should address:
1. Figure 1: should be technically improved, the legend covers exactly the threshold region
2. Is there some gas-phase data to compare with the calculated BEB CSs?
3. Figure 2: Please connect the experimental points by a line, so the experimental trend could be seen more readable.
4. Line 148 “This is a very strong indication … “:
a. Could the author comment on why the intensity of resonances is so much inverted between the gas phase and the condensed phase? Is there a possible physical reason?
b. Beside this, is there a possibility that higher energy electrons, after an inelastic scattering within the material (excitation processes) are left with an energy close to the low-DEA resonance? Thus, the increased reaction rate at higher energies is in fact also due to the low-energy resonant DEA (which is with a higher cross section)? Of course, the opposite is not possible thus apparently (seemingly) changing the reaction ratio.
5. Line 191: there should be “:” after “data”, no?
6. Line 193: I would say that an expression “… should be taken with a large grain of salt …” is a bit too much for a scientific paper …
Author Response
Thank you for your very constructive and helpful review.
I have redrawn all the figures to include experimental data for ionization cross sections, error bars on experimental data for product formation, better resolution and contrast, and have moved the figure legend out of the way. Also, I have included lines through experimental data to guide the eye.
I have very shortly addressed the question of way branching ratios in the condensed phase can be so different from gas phase. The electronic structure and thus the potential energy surfaces can be distorted quite drastically with respect to gas phase, especially in anionic states where the extra eletron can actually be delocalized to an extent where it overlaps with several neighboring molecules.
The question of energy loss by repeated inelastic scattering is a bit harder to address. Usually in the experiments portrayed here, film thickness is sufficienly small that there should be no significant energy loss. Also, it is not universally true that lower-lying resonances are pronounced in condensed phase experiments. So this is not a universal problem.
But it is not easy to conclusively rule this out for any given system.
And lastly, the grain of salt has been removed in exchange for a great deal of caution.
Thank you!
