Fragmentation Dynamics of ${\mathrm{CO}}_2^{\mathrm{q}+}$ (q = 2, 3) in Collisions with 1 MeV Proton

Round 1

Reviewer 1 Report

The authors have investigated the energetics of two formally simple ions, , CO₂²⁺ and CO₂³⁺. Their study documents the necessity of understanding few atom species so that larger species may also be understood -- I recall multiply charged ions in the mass spectra of biologically important compounds. Let me remain, however, in the relam of atoms, diatomcs and triatomics. I would appreciate if the authors, however briefly, would make comparisons of their results with the structures and energetics of neutral and singly charged isoelectronic analogs. For example,  CO₂²⁺ and CO₂³⁺ are so related to the isomeric pair NCN and CNN, and C₃^- respectively. Do the chemical rules and regularities I know, e.g. Walsh diagrams for linear and bent triatomics, apply here? What is known the excited states of these species -- e.g., what about the cyclic isomer of CN₂. So doing would add to the general utility of the current study for the non chemical physics reader.  Also, having taken some care here to use of subscripts and superscripts in my review, I ask the authors to go through their text and references and make sure that subscripts and superscripts for stoichiometry and charge respectively are correct. 

Author Response

We would like to thank the reviewer for reviewing our manuscript in detail and providing valuable input. We would like to present our reply to the reviewer's comments and revisions in the manuscript. Modifications in the manuscript are included in bold font. The revised manuscript is submitted for your consideration.

To address the issue raised by the reviewer we have added the following text on line 37:

"The CO₂²⁺ and CO₂³⁺ molecular ions are isoelectronic to the isomeric pair NCN and CNN radicals, which also have a linear geometry in the ground state. In photofragmentation studies, it has been shown that N₂ production from both CNN and NCN radicals is a dominant photodissociation channel [23-25]. This channel is attributed to the bent intermediate states of the free radicals.  The NCN and CNN radicals are important in combustion chemistry [24].  Recently, a similar fragmentation channel for CO₂²⁺ molecular ions producing O₂⁺ ionic fragment has also been observed in laser induced ionization and subsequent dissociation study [26].  The C₃^- radical is also part of the same isoelectronic family. It is relevant for plasma physics and hydrocarbon chemistry and is even found in the interstellar space [27,28]. Thus, the study of dissociation dynamics of CO₂^q+ (q=2,3) molecular ions can provide important information about different electronic states of these radicals."

As suggested by the reviewer, we have corrected the typos in the subscripts and superscripts in the text and the references and are denoted by underlines.

Reviewer 2 Report

Report on manuscript 2302083 Duley

 

“Fragmentation dynamics of CO^q+ (q = 2,3) in collisions with 1 MeV proton”

by A. Duley and A. H. Kelkar

 

 

 

The present manuscript reports on the fragmentation of CO molecular ions induced by 1 MeV proton impact. The fragmentation dynamics is deduced from COLTRIMS measurements by the use of Dalitz plots and Newton diagrams. The paper concentrates on two- and three-body fragmentation of CO dications and trications. Different dynamics are evidenced ranging from concerted fragmentation to sequential dissociation. The main results concerns the C+ + O+ + O+ channel for which a molecular bond stretching seems to precede the fragmentation. The paper is clearly written.

 

A few typo have to be corrected:

-          Page 1, line 24: replace “compared” by “compared”

-          Page 3, caption fig1: replace “… for (a) the TOF of the second ion …” by “… for (a) the TOF of the first ion …”

-          Page 3, line 93: the authors should consider to refer to more adapted references instead of ref 17 and 18. Several review papers on COLTRIMS might be better suited.

-          Page 3, line 98: replace “… orthogonal to theion beam and gas jey direction. Acceleration filed …” by “… orthogonal to the ion beam and gas jet direction. Acceleration field …”

-          Page 3, line 100: replace “Whereas the ions are …” by “The ions are …”

-          Page 3 line 101: a number seems to be missing “an extraction field on followed by …”. Please complete

-          Page 3, line 107: replace “Th time-of-flight …” by “The time-of-flight …”

-          Page 3, line 118: replace “… ion with smallest …” by “…ion with smallest …”

-          Page 6, line 184: replace “Hence, the the slope …” by “Hence, the slope …”

-          Page 7, caption fig 3: replace “… (a) …” by “… (c) …”

-          Check the reference list. Many subscripts and exponents are wrongly written for the molecular ions.

 

 

 

In conclusion, the paper presents new experimental results which worth to be published in Atoms.

Author Response

We would like to thank the reviewer for reviewing our manuscript in detail and providing valuable input. We would like to present our reply to the reviewer's comments and revisions in the manuscript. Modifications in the manuscript are included in bold font. The revised manuscript is submitted for your consideration.

Comment: Page 1, line 24: replace “compared” by “compared”

Reply: Corrected.

 

Comment: Page 3, caption fig1: replace “… for (a) the TOF of the second ion …” by “… for (a) the TOF of the first ion …”

Reply: Corrected.

 

Comment: Page 3, line 93: the authors should consider to refer to more adapted references instead of ref 17 and 18. Several review papers on COLTRIMS might be better suited.

Reply: As suggested, we have replaced both the references by the following two references:

Ref.31 (earlier ref 17) Döner, R.; Mergel, V.; Jagutzki, O.; Spielberger, L.; Ullrich, J.; Moshammer, R.; Schmidt-Böcking, H. Cold Target Recoil Ion Momentum Spectroscopy: A ‘Momentum Microscope’ to View Atomic Collision Dynamic. Phys. Rep. 2000, 330, 95-192 https://doi.org/10.1016/S0370-1573(99)00109-X.

Ref.32 (earlier ref 18) Ullrich, J.; Moshammer, R.; Dorn, A.; Dörner, R.; Schmidt, L. Ph H.; Schmidt-Böcking, H. Recoil-ion and electron momentum spectroscopy: reaction-microscopes. Rep. Prog. Phys. 2003, 66, 1463-1545 https://iopscience.iop.org/article/10.1088/0034-4885/66/9/203.

 

Comment: Page 3, line 98: replace “… orthogonal to theion beam and gas jey direction. Acceleration filed …” by “… orthogonal to the ion beam and gas jet direction. Acceleration field …”

Reply: Corrected.

 

Comment: Page 3, line 100: replace “Whereas the ions are …” by “The ions are …”

Reply: Corrected.

 

Comment: Page 3 line 101: a number seems to be missing “an extraction field on followed by …”. Please complete

Reply: Corrected and now the line reads: "The ions are extracted using an extraction field of 145 V cm^-1 followed by an accelerating field of 260 V cm^-1 towards a microchannel plate of 40 mm diameter equipped with a delay line anode."

 

Comment: Page 3, line 107: replace “Th time-of-flight …” by “The time-of-flight …”

Reply: Corrected.

 

Comment: Page 3, line 118: replace “… ion with smallest …” by “…ion with smallest …”

Reply: Corrected.

 

Comment: Page 6, line 184: replace “Hence, the the slope …” by “Hence, the slope …”

Reply: Corrected.

 

Comment: Page 7, caption fig 3: replace “… (a) …” by “… (c) …”

Reply: Corrected.

 

Comment: Check the reference list. Many subscripts and exponents are wrongly written for the molecular ions.

Reply: Subscripts and exponents are corrected and are denoted by underlines.

Reviewer 3 Report

Authors are presenting an experimental investigation of the fragmentation dynamics of CO2 di and trication upon impact of neutral CO2 by 1 MeV protons. The work can be published after considering these major comments:

1) Authors should develop in the introduction the need and the impact of studying such processes.

2) Previous works, both theory and experimental should be cited in the introduction, e.g.  Ref.
    DOI: 10.1088/0953-4075/31/10/007.

3) Table 1: Authors are not considering (in my sens) the major channel CO2^2+ --> O+ (4^S) + CO^+ (X2^Sigma^+) channel for which a KER of 6 eV was determined theoretically and experimentally. Why?

4) The formation of O_2^2+ from CO_2^2+ was never evidenced experimentally. Why considering this channel?

5) In general, the discussion lacks the comparison of the available data from the literature. This should be done.

6) Figure 1 caption should be corrected: it is not "the TOF of the second ion versus the TOF of the second ion and"

7) Several typos are found. e.g. comapred, theion beam and gas jey direction, ...

 

 

Author Response

We would like to thank the reviewer for reviewing our manuscript in detail and providing valuable input. We would like to present our reply to the reviewer's comments and revisions in the manuscript. Modifications in the manuscript are included in bold font. The revised manuscript is submitted for your consideration.

Comment 1: Authors should develop in the introduction the need and the impact of studying such processes.

Reply: The introduction has been modified, three new references have been added, and the text from line 1 onwards now reads:

"Over the past few decades, the fragmentation dynamics of multiply charged molecular ions have been studied extensively. These studies are of fundamental interest as they help identify and understand the electronic states of molecular ions. Knowledge of these electronic states works as a verification tool for state-of-the-art theoretical models. These studies are also crucial in plasma and fusion research [1], atmospheric and space physics [2], and radiation therapy [3,4]."

Comment 2: Previous works, both theory and experimental should be cited in the introduction, e.g.  Ref. DOI: 10.1088/0953-4075/31/10/007.

Reply: A few references have been added on line 33, and the text now reads:

"Fragmentation dynamics of CO2 has been studied experimentally using highly charged ions at slow [5], intermediate [6], and swift velocity [7–10], synchrotron radiation [11,13], femtosecond laser pulse [14–16], as well as slow protons [12] and low energy electrons [17-19]. In addition, extensive theoretical studies [17, 20-22] complement the experimental results."  

  

Comment 3: Table 1: Authors are not considering (in my sens) the major channel CO2^2+ --> O+ (4^S) + CO^+ (X2^Sigma^+) channel for which a KER of 6 eV was determined theoretically and experimentally. Why?

Reply: We have added this channel in the text, and line 160 now reads:

"In their experiment with 1.3 keV electron, Sharma et al. [17] obtained a KER around 5.9 eV and from their ab initio calculations assigned this peak to the ³Σ_g^- state of the CO₂²⁺ molecular ion dissociating into O⁺ (⁴S) + CO⁺ (X²Σ⁺)channel."

Comment 4: The formation of O_2^2+ from CO_2^2+ was never evidenced experimentally. Why considering this channel?

Reply: To the best of our knowledge, there are no experimental or theoretical studies claiming the formation of O₂²⁺ from CO₂²⁺ molecular ions in collisions with electrons, ions, or photons. We are considering this channel as a possible deferred charge separation process. To emphasize the fact that this channel has never been observed, we have added the following text in line 225:

"...ejection of a neutral C atom and to the best of our knowledge, this particular channel has never been observed experimentally."

 

Comment 5: In general, the discussion lacks the comparison of the available data from the literature. This should be done.

To address the issue raised by the reviewer we have modified the text which now reads:

Line 36 - "In addition, extensive theoretical studies [17, 20-22] complement the experimental results."

Line 160 - "In their experiment with 1.3 keV electron, Sharma et al. [17] obtained a KER around 5.9 eV and from their ab initio calculations assigned this peak to the ³Σ_g^- state of the CO₂²⁺ molecular ion dissociating into O⁺ (⁴S) + CO⁺ (X²Σ⁺)channel."

Comment 6:  Figure 1 caption should be corrected: it is not "the TOF of the second ion versus the TOF of the second ion and"

Reply: Corrected and the line now reads: "..the TOF of the second ion versus the TOF of the first ion and.."

 

Comment 7:  Several typos are found. e.g. comapred, theion beam and gas jey direction, ...

Reply: Corrected and the corrections are shown in bold texts.

Reviewer 4 Report

The manuscript describes results of a study of the fragmentation dynamics of CO2^q+ (q=2,3) in collisions with 1MeV protons, carried out at the 1.7 MV Tandetron Accelerator Facility.  The experiments were performed using a recently built recoil ion momentum coincidence spectrometer. The presented data are of high quality, two- and three-body break-up channels of the dication and the complete fragmentation of the triply charged ion are analyzed. From the obtained kinetic energy and momentum distribution, and available literature data fragmentation mechanisms are suggested. The manuscript contains sufficient references to previous work for the reader to follow the analysis procedures.

In my opinion the manuscript should be published, but would benefit from some revision. Some additional details should also be included. Some attention should also be paid to the ‘Conclusions’ section, which at the moment mainly contains a list of arguments treated in the manuscript.

Experimental section:  Could the authors indicate the kinetic energy resolution and maximum detectable energies for those measurements? Reference 19 (now published) describes various modes of operation of the spectrometer, but numbers applying to the presented data sets directly in the manuscript would be helpful. The second question is about the (possible) selectivity in the electron detection. The acceptance angle of the electron detector is deliberately kept rather small (ref 19). Does this introduce any (energy) selectivity in the electron detection? Such selectivity could affect the observed intensity ratios between different dissociation channels. What was the observed intensity ratio between the doubles and triples channels?    

Two-body dissociation: the two-body complete dissociation channel of the dication shows a clear contribution of a metastable state. The authors derive the lifetime of that decay, and indicate the final V-shape as due to the dissociation in the field-free region of the apparatus. Can this KER be recovered from the data? If yes, how does it compare with the energies and states plotted in figure 2?

Three body fragmentation of the dication (C+ + O+ + O) (fig 3 (a) & (d)): The observed distribution is interpreted as a combination of two processes, in qualitative agreement with an electron impact study (ref 13).  Authors also consider the possible contribution from an incomplete detection of a triple coincidence. Can the authors estimate relative importance of ‘undetected triples’ in the analysis?

Section 3.5.2 describes the O+ + O+ + C channel. In the paragraph C+ ions and O atoms are also included, discussing the axes and angles. Could the authors clarify this part? The O+/O+ coincidence detection will suffer most from the detector deadtime. How does this influence the derived KER?  

Triple ionization (Figure 5c in my version has some problems): Reference 8 describes an experiment on the same system at lower projectile energies. The studied channel is the complete dissociation of the triply ionized ion. As a continuation that paper suggests experiments at higher projectile energies, where possibly inner shells of the target can be accessed. Could the authors comment on this, in view of the current results?   

General points:

Abstract (line 4), the use of ‘slopes’ seems premature, as it has not been defined yet. Maybe the sentence could be just removed.

Introduction: It should be checked for consistency, as statements applicable to molecules in any charge state are mixed with the characteristics specific to triatomic multiply charged linear targets. Both things can be included, but currently the order seems rather random.

The current manuscript contains many typos, a spellchecker and careful proofreading should take care of this.

Figures: In my version Fig 5c does not show any shading (mentioned in the text in line 365) and no overall KER. What do the arrows in that figure indicate?

Same question for the vertical scaling factors in figures – is the intensity after scaling comparable, or is it just for better visibility?

References – reference [2] seems correct (as intended), but the title does not match the paper

 

Author Response

We would like to thank the reviewer for reviewing our manuscript in detail and providing valuable input. We would like to present our reply to the reviewer's comments and revisions in the manuscript. Modifications in the manuscript are included in bold font. The revised manuscript is submitted for your consideration.

• Some attention should also be paid to the ‘Conclusions’ section, which at the moment mainly contains a list of arguments treated in the manuscript.

We have modified the 'Conclusions' section as suggested and the text reads:

"We have studied the dissociation dynamics of a simple, linear triatomic molecule CO₂ under the impact of 1 MeV protons. We have measured the two- and three-body dissociation of doubly and triply charged molecular ions of CO₂. For the O⁺+CO⁺ fragmentation channel from the CO₂²⁺ molecular ion, we see a prompt dissociation resulting in narrow KER distribution. {This KER distribution can be well explained based on the different electronic states reported by earlier theoretical and experimental studies. The CO₂²⁺ molecular ion also shows a metastable character in the ion-ion correlation diagram as a tail and 'V' structure. Using the intensity of these structures, we have estimated the life time of the metastable (CO₂²⁺)^* molecular ions. We have also discussed the three-body dissociation of  CO₂²⁺ which produces two ions and a neutral. All three-body dissociation are discussed using Dalitz plots, Newton Diagrams, and angular distributions. For both the C⁺+O⁺+O and O⁺+O⁺+C channels we have observed contribution from both concerted decay. In addition, for the C⁺+O⁺+O channel we see signature of an s(i)₂ process, whereas in the O⁺+O⁺+C channel contains signature of an s(i)₁ process. The contributions from all these processes are also be verified from the angular distributions. We have further discussed the charge symmetric fragmentation of CO₂³⁺ molecular ions producing  C⁺+O⁺+O⁺. The angular distributions for this channel hint towards the fact that the three-body fragmentation is happening from bent molecular geometries of the precursor molecular ions. The Dalitz plots and Newton diagrams further suggest that molecular bond stretching precedes the fragmentation process in this charge symmetric dissociation. The linear triatomic CO₂ molecule has three vibrational modes, namely symmetric stretching, asymmetric stretching, and bending vibration. The typical time scales of these three stretching modes are 25 fs, 14 fs, and 50 fs [50], respectively, which are much larger than the interaction time (t_int) of 37 as for the present collision system consisting of 1 MeV protons and CO$_{\text{2}}$ molecules. The population of these different vibrational modes depends on the available energy of the molecular system. The KER distribution works as a tool to investigate different energy regimes in the fragmentation process. In the lowest KER range, we have observed that the fragmentation is happening due to concerted decay from a linear geometry of the precursor molecular ion (synchronous decay). With the increase in KER values, we observe more contributions from the bending and asymmetric stretching (asynchronous decay) modes."

• Experimental section:  Could the authors indicate the kinetic energy resolution and maximum detectable energies for those measurements? Reference 19 (now published) describes various modes of operation of the spectrometer, but numbers applying to the presented data sets directly in the manuscript would be helpful. The second question is about the (possible) selectivity in the electron detection. The acceptance angle of the electron detector is deliberately kept rather small (ref 19). Does this introduce any (energy) selectivity in the electron detection? Such selectivity could affect the observed intensity ratios between different dissociation channels. What was the observed intensity ratio between the doubles and triples channels? 

Reply: We have added the following text on line 111:

"The present spectrometer conditions result in a KER resolution of ~ 1.2 eV for three-body fragmentation and a 4Π collection efficiency of particles having energy < 8 eV/q."

 

The electron acceptance angle was kept small to reduce the electron counts on the Channeltron detector. This leads to collection of electron mainly along the spectrometer axis and electrons ejected in the perpendicular plane, with energy more than 1 eV, are not collected.  However, the target gas molecules are oriented randomly in space. Therefore, all fragmentation channels are detected with equal likelihood.  As result the relative intensities of different fragmentation channels would depend only on the population of different electronic states and the detection efficiency of the spectrometer.

The relative intensities (normalized to the total counts) of different channels are as shown below are as expected for different degrees of parent ionization. 

O⁺+CO⁺: 34.87%

C⁺+O⁺+O: 47.89%

O⁺+O⁺+C: 15.06%

C⁺+O⁺+O⁺: 2.18%

 

 

• Two-body dissociation: the two-body complete dissociation channel of the dication shows a clear contribution of a metastable state. The authors derive the lifetime of that decay, and indicate the final V-shape as due to the dissociation in the field-free region of the apparatus. Can this KER be recovered from the data? If yes, how does it compare with the energies and states plotted in figure 2?

The KER due to the fragmentation of this metastable molecular ion can not be obtained using the present data analysis method. One could simulate the fragmentation of CO₂^2+* in the drift tube having some initial momentum distribution and try to estimate the KER values due to the fragmentation resulting into the 'V' shaped island in the coincidence plot. The simulation results can then be further used to get an idea about experimental values. As stated earlier, this is currently beyond the scope of our capabilities.

• Three body fragmentation of the dication (C+ + O+ + O) (fig 3 (a) & (d)): The observed distribution is interpreted as a combination of two processes, in qualitative agreement with an electron impact study (ref 13).  Authors also consider the possible contribution from an incomplete detection of a triple coincidence. Can the authors estimate relative importance of ‘undetected triples’ in the analysis?

The ion-detection efficiency (D) of the spectrometer is the product of the overall transmission efficiency (T) of the meshes and the detection
efficiency of the MCP (f). Since, we have used three high-transmission (95%)
meshes, the value of T was estimated to be 86%.

The detection efficiency of an MCP detector is proportional to the velocity of
the impinging particle [Savin et al., Rev. Scl. Instrum., 66, 67 (1995)]. Hence,
for a given MCP front voltage, ions with small m/q ratio are detected with
greater efficiency than those with large m/q. As a result, the MCP detector
needs to be operated in the saturation region so that it can detect all ions with
equal efficiency. To determine this saturation region, we studied the multiple
ionization of atomic argon (Ar). In particular, we kept a fixed potential difference of 1900 V across the stack and obtained the ratio of Ar⁺ to Ar²⁺ intensity
as a function of MCP front voltage. For our experiments, -2700 V is found to
be the optimal voltage . In the saturation region, the value of f can be taken to
be the open area ratio of the MCP (>50%, RoentDek) [Bhatt et al., Phys. Rev.
A 82, 044702 (2010)]. Hence, for the present spectrometer the D was estimated
to be 48%. This the efficiency for detecting a single ion. The efficiency would
go down for double and triple coincidences, which are estimated to be 23% (D²) and 11% (D³), respectively.

• Section 3.5.2 describes the O+ + O+ + C channel. In the paragraph C+ ions and O atoms are also included, discussing the axes and angles. Could the authors clarify this part? The O+/O+ coincidence detection will suffer most from the detector deadtime. How does this influence the derived KER?  

Reply: We apologize for the confusion arising due to the typos. The angles α and γ are defined with respect to the C atom, not the C⁺ atom, and there are no O atoms in this channel. The corrected text on line 320 now reads:

"The two O⁺ ions show peak structure around 160^o (α) and 125^o (γ), with a small contribution around 160^o in the distribution of the angle γ. Whereas the angle β has a broad distribution around 110^o."

The O⁺/O⁺ coincidence detection will suffer most from the detector deadtime. As a result we will loose fragment ions produced in the perpendicular plane of the spectrometer axis. Now, in reference 33 (earlier ref 19), where we studied fragmentation of N2 molecules under the impact of 1 MeV proton, we have discussed the N+/N+ fragmentation channel in terms of the kinetic energy release distribution (KERD). This KERD matches well with the existing theoretical and experimental data. Thus, although the equal mass to charge ration affects the counts detected in a particular fragmentation process, the KERDs turns out to be reliable.

• Triple ionization (Figure 5c in my version has some problems): Reference 8 describes an experiment on the same system at lower projectile energies. The studied channel is the complete dissociation of the triply ionized ion. As a continuation that paper suggests experiments at higher projectile energies, where possibly inner shells of the target can be accessed. Could the authors comment on this, in view of the current results?   

Reply: We believe Figure 5c is correct, but the text was incorrect. We have corrected the text from line 373 onwards:

"The kinetic energies (KEs) of the individual fragments for the C⁺ + O⁺ + O⁺ channel is shown in Figure 5(c). In Figure 6 (a, b, c), we have plotted the complete KER distribution for the above channel in three regions: (a) 0-9.6 eV, (b) 9.6-16.8 eV, and (c) 16.8-35.0 eV. The KER spectrum has a most probable value of 7.2 ± 0.4 eV (Figure 6 (a)) with a broad structure around
20 eV (Figure 6 (c)). It extends form 0 eV to around 35 eV. The most probable value of KE (the position of which are depicted as arrows in Figure 5 (c)) are 1.5 ± 0.05 eV, 1.5± 0.1eV, and 0.5 ± 0.04 eV for C⁺, O⁺, and O⁺, respectively. "

In our present experiment with 1 MeV protons, there is a possibility of inner shell ionization, which can produce CO₂³⁺ molecular ions through the Auger-Meitner cascade. The current set up does not have an electron analyzer which would help to detect energy-selected electrons. Hence, it is not possible to separate out the inner shell ionization from multiple ionization from the valance shell.

 

• General points:

• Abstract (line 4), the use of ‘slopes’ seems premature, as it has not been defined yet. Maybe the sentence could be just removed.

Reply: Removed the sentences as suggested.

 

• Introduction: It should be checked for consistency, as statements applicable to molecules in any charge state are mixed with the characteristics specific to triatomic multiply charged linear targets. Both things can be included, but currently the order seems rather random.

Reply: The text has been modified and line 21 now reads:

"A multiply charged (charge state more than 2) molecular ion usually goes to an unstable state and eventually fragments into atomic ions and neutrals due to the Coulomb repulsion between the ionic cores." 

• The current manuscript contains many typos, a spellchecker and careful proofreading should take care of this.

Reply: The typos have been corrected.

• Figures: In my version Fig 5c does not show any shading (mentioned in the text in line 365) and no overall KER. What do the arrows in that figure indicate?

Reply: We have modified the text to clarify these two issues and the text reads as following from line 373 onwards:

"The kinetic energies (KEs) of the individual fragments for the C⁺ + O⁺ + O⁺ channel is shown in Figure 5(c). In Figure 6 (a, b, c), we have plotted the complete KER distribution for the above channel in three regions: (a) 0-9.6 eV, (b) 9.6-16.8 eV, and (c) 16.8-35.0 eV. The KER spectrum has a most probable value of 7.2 ± 0.4 eV (Figure 6 (a)) with a broad structure around
20 eV (Figure 6 (c)). It extends from 0 eV to about 35 eV. The most probable values of KE (the position of which are depicted as arrows in Figure 5 (c)) are 1.5 ± 0.05 eV, 1.5± 0.1eV, and 0.5 ± 0.04 eV for C⁺, O⁺, and O⁺, respectively. "

We have also modified the caption of Figure 5 and now it reads:

"The KER distributions for the three-body fragmentation of CO₂^q+ (q=2,3) into (a) (1,1,0) and (b) (0,1,1) channels along with the kinetic energies (KEs) of the individual fragments. (c) KEs of individual fragments in the (1,1,1) channel. The arrows show the position of the most probable KE of each fragments. The scaling is performed for visual clarity."

• Same question for the vertical scaling factors in figures – is the intensity after scaling comparable, or is it just for better visibility?

Reply: The scaling is just for better visibility.

• References – reference [2] seems correct (as intended), but the title does not match the paper

Reply: Corrected.

Round 2

Reviewer 3 Report

Authors considered all my comments.