Probing the Fragmentation Pathways of an Argon Dimer in Slow Ion–Dimer Collisions
Round 1
Reviewer 1 Report
Report on manuscript 2157774 Siddiki
“Probing the fragmentation pathways of an Argon dimer at slow electron transfer collisions”
by M.A.A.Siddiki et al
The present manuscript reports on the different fragmentation pathways experienced by Ar dimers after collision with low energy projectiles and depending on the active processes, whether it is single capture, double capture, single ionization, transfer-ionization, transfer-excitation or double ionization, or combinations of those processes. From the Kinetic Energy release spectra of 2 fragmentation channels (Ar+ + Ar+ and Ar+ + Ar2+), measured by COLTRIMS technique, the contribution of the different fragmentation processes (Coulomb Explosion CE, Radiative Charge Transfer RCT, Interatomic Coulombic Decay ICD, …) are identified and their contribution are determined. These results are obtained using a newly developed COLTRIMS set-up at TIFR, Mumbai, India. From presented spectra, one can see the good performances of the setup. This paper nicely shows the interplay between the collision process, whether it is acting on one site or two sites, and the fragmentation process (CE, RCT, ICD). Furthermore, a strong angular dependence is evidenced and interpreted as a consequence of the fact that the impact parameter at which the collision process occurs is smaller than the interatomic distance within the dimer.
The paper presents new and interesting results, and is clearly written. Nevertheless, a few changes would improve it further:
- I would suggest to revise the title as it may confuse the reader thinking that collisions with slow electrons are concerned
- Page 2, line 43: replace “Coulomic” by “Coulombic”
- Page 4, line 90: replace “we have tabulated the results for the above” by “we have tabulated the measured yields”
- Page 4, line 91: The sentence seems to say that dimer cations are produced during the supersonic jet expansion. Is this sure?
- Page 4, line97: “The distributions of the different capture channels … in fig 3.” This sentence is not clear. It seems that fig.3 is the projection of the projectile detector image. Is it the case? If yes, then please correct also the figure caption.
- Page 4, caption of fig.2: The relative yields are relative to what? Please correct.
- Page 5, line 128: replace “R-dependent probability.” By “ R-dependent radiative decay probability.”
- Page 5, line 132: replace “… the RCT process implies the quasi-resonant …” by “… the RCT process is due to the quasi-resonant …”
- Page 6, line 135: replace “… smaller KER yield in that region.” By “… smaller KER yields at 3.65 eV.”
- Page 6, line 138: Which “two processes” are concerned?
- Page 6, line146 to 148: How the conclusion that capture is involved in both centers is reached? Why single ionization (SI) cannot occur?
- Page 6, line 153: “ both SI+TI and SC+DI channels contribute equally”: How this statement is deduced?
- Page 7, line 165: “Therefore, it does not prefer near-site or far-site DC, i.e., both DC+SI or SI+DC seem equally probable.”: How this statement is justified? Could far-site/near-site be explained clearly?
- Page 7, line 171 to 173: Again, the fact that the near- and far-site are not clearly defined makes the sentence difficult to understand. Usually, the near-site is the atom for which the projectile has the smallest impact parameter. It is not the first atom encountered by the projectile. It seems that in the paper, it is the second definition which is used. There is a need for clarification in order to understand the tentative conclusions.
In conclusion, the paper presents for sure very new and interesting experimental results. However, some parts of the discussion are not clear and need to be improved. So I encourage the authors to add the recommended revisions prior to publication.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors present electron capture and the following fragment processes of van der Waals (vdW) molecules, argon dimers, colliding with highly charged ions (HCIs) (2.5 keV/u, O2+) . Double coincidence measurements are carried out with the COLTRIMS technique. The authors analyze the results carefully and determine possible fragmentation pathways from various ones for Ar+- Ar+ and Ar2+- Ar+ channels. In the later channel, moreover, the orientation effect is discussed from the angular distribution of the fragment ion pairs with respect to the projectile beam axis. The analysis of fragmentation of vdW dimers by collision of HCIs are quite useful to understand the electron dynamics during transient molecular ions. In addition, the authors provide much information of their experimental setup, especially, the supersonic jet assembly. Therefore, the paper could be of quite interest for researchers. I think however that there are a few improvements that should be made before publication:
1. The authors need to mention detection efficiency of the neutrals and the ions of MCP for the projectiles, because they showed the relative yield of the resulted fragmentation channels.
2. In the manuscript, acronym of TI has two meanings. In order to avoid misunderstanding among readers, the author should distinguish them.
3. The right sides of eqs. (7) and (8) need one more electron to balance charge.
4. In the beginning of section 3.2, the authors should give instruction to see Fig. 5 (left) to readers.
5. In the discussion of the orientation effect, I wonder if the deflection of the projectile after collision were observed in Fig. 3.
Author Response
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Author Response File: Author Response.pdf
