Observation of Light-Induced Reactions of Olefin–Ozone Complexes in Cryogenic Matrices Using Fourier-Transform Infrared Spectroscopy

Round 1

Reviewer 1 Report

This paper reported IR vibrational spectra of four types of olefin-ozone complexes and presented possible assignments of photoproducts according to their IR featured bands. Some agreements were achieved between experimental measurement and theoretical simulation. This supported the author's tentative assignment on the photoproducts, especially for C2H4-O3 system. The concept of this work is interesting to the field of photochemistry. However, the paper is not organized and presented well, in terms of the format and content. Some arguments are not well supported by the results. I would suggest a major revision for the paper until the paper is written in a more scientific way and the results are convincing. Below are some parts I feel necessary for revision.

(1) The introduction part need more systematic background and motivation for the project, such as more discussions on previous investigations in the literature.

(2) In the Materials and Methods, the authors should also give details for computational methods, indicating which parts are from previous reports and which parts are done by the author. For example, it is confusing if the author did the anharmonic vibrational spectra calculations and how those calculations were done.

(3) The figures in the current paper are not ordered properly. Besides, the axis of IR spectra do not have clear xtics which make it hard to find the exact positions of different vibrational bands. The author should also take care of the resolutions of figures.

(4) In Page 4, line 100-105, the text are confusing and should be formatted in a scientific way

(5) Table 1 gives the peak positions and their assignment to different products. However, the author should indicate explicitly which vibrational bands of these peaks in different products. It is not convincing and not clear to make a one-to-one pair comparison.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Light-induced reactions between 4 compounds (a series of olefins) and ozone are reported. The reactions were studied in cryogenic Ar matrices by irradiating samples with various light beams  (UV-Vis). The products of photoreactions were studied using IR spectroscopy. Additionally, DFT calculations of vibrational spectra of some expected products were performed; the calculated spectra were used for identification of compounds. I think that these are quite interesting results which probably deserve publication, nevertheless I have many critical remarks related to both the experimental data and the way of their presentation.   

• There is a lot of mess in the manuscript. Figures are not displayed in order. I wonder why the Fig. 6 is presented just after Fig. 1. Some other figures are also displayed in a strange order.
• Most of the figures are not acceptable. Why the data are not presented in a traditional form? Why the abscissa does not show wavenumbers?
• Information about the power of light beam used for irradiation is missing. It seems to me that for each spectrum the time of irradiation should be given.
• Fig. 6 on page 3. Why the most upper black line is longer? Why the spectra of olefins after reaction with ¹⁶O₃ and ¹⁸O₃ are so different? This difference is surprising and should be discussed in more detail.
• Fig. 2 on page 4. Vibrational bands at 867, 1726 and 2343 cm^-1 are not seen, in the scale of the figure at least. Why other bands are not assigned?
• Fig. 3 on page 9. I cannot see peaks at 822, 923 and 993 cm^-1. What does show the wavenumber 1749 cm^-1? The dotted line corresponding to 1749 cm^-1 lies in the neighborhood of a rather strong band. Where is a band of the CO molecule? Why some bands are not assigned?
• Fig. 4 on page 10. For each irradiation we see two overlapping spectra which exhibit quite significant difference. What do mean the oblique straight lines? It is impossible to find a band at 917 cm^-1. Why so many bands are not assigned?
• Fig. 5 on page 11. My critical remarks are similar to those given for Fig. 4.
• Figs 8, 9 and 10. I appreciate that the Author has performed DFT calculations of vibrational spectra of 8 compounds which potentially could be products of photoreactions, however the calculated bands should be assigned and compared with the experimental spectral features. Usefulness of the calculated spectra presented in the figures is rather small.
• All the vibrational features observed in the experimental spectra should be collected in a table, together with the proposed assignment either based on literature or DFT data.

Taking into account the above critical remarks and also many other not-expressed doubts, I think that  the manuscript in the present form cannot be accepted for publication in Photochem.

Author Response

Thank reviewer 2 for reading my manuscript patiently. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript ID: photochem-1584276

Title: Observation of light-induced reactions of olefin–ozone complexes in  cryogenic matrices using Fourier-transform infrared spectroscopy 

By  Fumiyuki Ito

 

This paper deals with light-induced reactions of selected olefins with ozone. The author uses matrix isolation technique coupled with infrared spectroscopy. The subject is not new although still important being relevant to the atmospheric chemistry.

The manuscript is difficult to follow because of several reasons.

1. Introduction is much to short especially that the lines 36-39 should be rather moved to Materials and Methods. There is a lot earlier papers published on ozone reactions with different alkenes both in the gas phase and in low temperature matrices. For example papers by Hs.H. Gunthard or B.S. Ault (one work of the latter author is cited in discussion).  A short review of these as well as newer results available in the literature should be given in the introduction.
2. In Material and Methods neither spectral resolution nor studied range are given.
3. Results:

• There is a random order of the figures in this chapter. This makes reading additionally difficult.
• Difference spectra are presented to show the obtained results. Why only 700-2400 cm^-1 range is presented? Why in some cases so badly purged system was shown? There is no information on the intensity of the newly formed product bands.
• Lines 106-108. Please, explain this statement.
• Two sentences: lines 109-110 and 114-115 contradict each other.
• Lines 111-113. Where are these data from? If the first reaction takes place in the studied matrices, the author should observe water bands in the spectra. Please comment on this subject.
• The entire chapter is not clear and the author is recommended to work on it.
• Lines 194-195. What does it mean “two peaks cannot be mixed up”?
• Line 201. Which “both molecules”?
• Line 203. Would be better to change “temporarily” into tentatively
• If the 1740 cm^-1 band is assigned to vC=O in the 3-methyl -2-oxobut-3-enal molecule there should be a second band at slightly different wavenumber. What information on this subject can be obtained from the performed calculations?
• Lines 215-216. Which “two candidate” molecules?

General comment to improve Results chapter: The experimental results should be discussed in conjunction with the results of the calculations. Are the observed bands predicted to be the most intense for a given product? If not , why the remaining intense bands are not observed?

• In Fig.7 one of the product does not have a name. Values of the calculated energy are not necessary and should be removed.
• The numbering of the figures is doubled.

4. References: the numbering of the references is doubled.
5. The author is encouraged to correct English, which is not clear in some places.

Summarizing, the paper is probably publishable  however it requires major revision.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been improved significantly and solved my questions. I would suggest to accept it.

Author Response

Again, the author would like to thank reviewers for critical reading of the revised manuscript.  He is glad to find that the last revision sufficed for acceptance.  Following changes were made upon request of reviewer 2 in this revision.

(1) The big noise in the 1300-1500 cm^-1 region due to the fringe and resulting intensity degradation is very annoying and it can mess up the whole figure especially when it is subject to copy-and-paste in a vector format.  So in this revision the author decided to trim this part whenever necessary.  It was explained in the main text, as well as in figure captions.
(2) Figs. 2-5 were modified accordingly.  Figure captions were also modified.
(3) Fig. 6 was modified accordingly.  The reason of the isotopic experiments was as follows: we found a peak of photoproducts at around 900 cm^-1 (923 for butadiene, 917 for isoprene), and at first we suspected it originated from the Criegee intermediate CRR'-O₂.  If so, the vibrational peak should show large isotopic shift upon ¹⁸O substitution (900 cm^-1 band corresponds to O-O stretching mode).  It turned out that it was not the case.  As a matter of fact, the isotopic dependence of C=O stretching frequency is just to ensure that the carrier .  A brief account was added to the main text.
(4) Figs. 8-10 were modified accordingly.  
(5) Table 1 was modified accordingly.
(6) The main text was checked by Grammarly.  Further English editing by a proof-reading company was not done due to the limited time for revision.
(7) A brief acknowledgement was added for reviewers.

Reviewer 2 Report

Thank you for taking into account my critical remarks and modification of the manuscript. I think that the manuscript is improved, nevertheless I think that it still requires next corrections.

• Figs 2-5 have been changed. Now one can clearly see vinrational bands. However, these figures are very different form the previous ones. My impression is that other spectroscopic data are presented. In the axis “Absorbance” we see scales but these are not good scales since for better visibility the spectra were shifted along this axis. In my opinion the scale is appropriate only for the most bottom spectrum. Therefore, it would be better not to show the scales and use the axis description “Absorbance (arbitrary units)”.
• The Fig. 6 has been also improved. My above remark related to the scale “Absorbance” is also valid for this figure. However, I still do not understand why ¹⁶O₃ and ¹⁸O₃ were used. It would be nice, if the Author explained why experiments with both ¹⁶O₃ and ¹⁸O₃ are necessary.  
• Figs 8-10 are not acceptable - they must be improved. The most upper spectrum signed “obs.” should be found in Figs 3-5, respectively, but they cannot be found. Moreover, it is nearly impossible to find in the experimental spectra bands which were assigned to calculated vibrational features.
• Thank you for all the changes in Table 1. I think that the table can be accepted in this form, although it would be better if more calculated bands were assigned and compared with the experimental spectral features. It would be nice if an additional column with calculated data was introduced.
• Some small corrections (also typographical) of the text are still necessary.

In conclusion, after additional corrections (first of all Figs 8-10) the paper could be accepted for publication in Photochem.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript ID: photochem-1584276

Title: Observation of light-induced reactions of olefin–ozone complexes in cryogenic matrices using Fourier-transform infrared spectroscopy

Authors: Fumiyuki Ito

The authors did a lot of work to improve their manuscript according to the reviewers comments. The manuscript can be now published  in this form.

Author Response

Again, the author would like to thank reviewers for critical reading of the revised manuscript.  He is glad to find that the last revision sufficed for acceptance.  Following changes were made upon request of reviewer 2 in this revision.

(1) The big noise in the 1300-1500 cm^-1 region due to the fringe and resulting intensity degradation is very annoying and it can mess up the whole figure especially when it is subject to copy-and-paste in a vector format.  So in this revision the author decided to trim this part whenever necessary.  It was explained in the main text, as well as in figure captions.
(2) Figs. 2-5 were modified accordingly.  Figure captions were also modified.
(3) Fig. 6 was modified accordingly.  The reason of the isotopic experiments was as follows: we found a peak of photoproducts at around 900 cm^-1 (923 for butadiene, 917 for isoprene), and at first we suspected it originated from the Criegee intermediate CRR'-O₂.  If so, the vibrational peak should show large isotopic shift upon ¹⁸O substitution (900 cm^-1 band corresponds to O-O stretching mode).  It turned out that it was not the case.  As a matter of fact, the isotopic dependence of C=O stretching frequency is just to ensure that the carrier .  A brief account was added to the main text.
(4) Figs. 8-10 were modified accordingly.  
(5) Table 1 was modified accordingly.
(6) The main text was checked by Grammarly.  Further English editing by a proof-reading company was not done due to the limited time for revision.
(7) A brief acknowledgement was added for reviewers.