I have attached the Table of Characteristic IR Absorptions, you should download and compare. I hope that it is useful for you.

Thanks. But this table does not have what I'm looking for. Thanks anyhow.

What are you looking for ? What expected you ? This compound is a organic? inorganic? Have complexed metals ???

Hi man 1800 is region for carbonyl of anhydride and acid chloride and 2500 is for S-H remainings are C-H strechings

Do you have any idea on formula of the compound? I think that here you have some carboxylic group (1800 cm-1) in dimeric form (hydrogen bonded with neighbour carboxylic group), which is further supported by occurence of typical feature around 2500 cm-1 (which is due to carboxylic OH vibrators hydrogen-bonded to carboxyle C=O of the other molecule), and the rest of bands you're interested in are due to alkyl CH groups.

2550 cm-1 could also be a thiol S-H stretch. Some more info on the compound would be really helpful.

Yeah, some kind of information about the elements that could be involved and whether this is a solid, liquid, solution, etc. would make this much easier.

If you synthesised compound then regents will help you supremely so think about all posibilities other wise simple solution for comlete elucidation is to run sample for NMR

This is very dangerous question when so little information is known. All previous answers are possible but as all previous contributors have pointed out we need to know a lot more about solid/liquid, sample mounting, etc.. This is only a short spectrum. Why ? Are you using windows or a crystal that cuts off below 1750cm-1 or is it an inorganic carbonate with a very strong ~1400 cm-1 band ?

Thanks guys. The sample is actually fossil material. I don't know the exact identity of. We encountered these peaks on the seemingly void spaces of then living tissues. So, it's possible during the fossilization process a filling of some carbonates, and perhaps alkyl-bonded material. Also, these three peaks were only observed from the second focus plane of FT-IR, not from the first focus planes. We are very puzzled. Any help will be very highly appreciated. Other parts (identified) of the spectra were omitted.

As a fossil material it's necessary to identify its origin, if it's from plant or animal. Afterwards it's also necessary to check the chemistry elements more abundant on the process of fossilization. I think that this procedure will help to identify the peaks and the correspondent chemical groups.

To Nikola Biliskov,

Do you have an IR of what you mentioned: carboxylic group dimer?

To Marinonio Cornelio,

These fossils were animal.

To John Boyd,

I'm not familiar with XANES or EXAFS. What can these two tell us? We do have access to the facility of National Synchrotron Radiation Research Center here in Taiwan. In fact, our IR spectra were done using sr-FTIR there. As I mentioned earlier, we see these 'strange' peaks only from the 2nd focus plane (bottom) scans on the original void areas, not from the 1st focus plane (surface).

Hopefully attached is a Word document with two IR spectra of Calcium Carbonate. The former ,in absorbance, is a KBr disk spectrum. You will see bands similar to yours some of which are overtones from the strong 1400cm-1 band. The second, in transmittance, is a DRIFTS reflection spectrum which enhances the the weaker bands in this region. These small bands and the position of the 1400 cm-1 band change depending on the metal, purity and "crystallinity" of the carbonate. Remember not all bands can be assigned to a specific group. This is vibrational spectroscopy and the whole molecule vibrates. Some bands are there due to the shape or physical form of a molecule and the environment which it is in. Unless you wish to pursue an extended academic excerise in assignments do not try to over interpret these smaller bands.

Thanks, Geoffrey. I think I now have a good idea on what I'm looking for. I think what Nikola Biliskov said, carboxylic acid dimers fit our case better. Amides peaks were observed, but were omitted from what I posted.

Timothy, despite the ‘acid dimers suggestion’ may look as more scientific, I vote for Geoffrey’s interpretation. Please compare some spectra in the attached PDF-file. Obviously, the spectral fragment you’ve posted belongs to CALCIUM CARBONATE. As to the amides peaks observed, why not to show the full spectrum? It seems that amide bands in your case should be masked by the huge band in the 1700-1100 cm-1 range, but anyway I wish you good luck with the amides interpretation. Meanwhile, there is an excellent source of info about CaCO3 in the net

http://webbook.nist.gov/cgi/cbook.cgi?ID=C471341&Mask=80

Thanks. We did not exclude the existence of carbonates. However, there are some organic contributions from the fossils we scanned.

Please see this NIST calcium carbonate IR. There is no peak at 1795, ~2500, and ~3000 cm-1. Naturally formed calcite contains some organics! Also aragonite, also calcium carbonate could exist inside fossils.

Thanks Rohit.

There are very small amount of other information which could help to assign these bands. The peak around 1800 is a range where the IR absorptions are very rare, e.g. in case of CO, NO or B-O frequencies can be found here. B-O frequency range is very wide, depending on the ligands around boron, and borax or other borates can react with organic components to form B-O bond compounds.

Is this fossil is conservated artificially (e.g. with borax) or by the nature ?

If yes, I would concentrate on this field, e.g. for the reaction of borax and amino acids, SH-contg. amino acids, or degradation product of amino acids, etc.

Furthermore, I am not satisfied, that all the peaks belong to one compound.

I had a case when I had a gas inclusion in my sample (N2O in a mixed NH4NO3 and CuMn2O4 mixture) and the IR peak (very narrow) was hard to identify. Now, the peak around 1800 is not enough arrow to be gas inclusion.

The highest bands can belong to CH, but the peak around 2500 is located again an unusual range. B-H, S-H are the typical in this range. B-H bond containing compounds are air and moisture-sensitive, so these can be disclosed.

I think, a result about elemental components, e.g. metals would give a tool to decide whether it is an inorganic or organic compound/compound mixture. If you cannot destroy the sample to measure the metal content, an XRF or ESCA analysis could give some qualitative information about the presence of inorganic elements, but a simple SEM would give some information.

I would check the presence of boron first.

Furthermore, the peak around 2500 is a double peak, and the origine of the sample conduct me to study the reaction products/degradation products of biological compounds, e.g. amino acids, thiol-group contg. amino acids, etc.

I would do a Raman spectrum as well, because the change in relativ intensities/appearance/disappearance of bands could give some further information.

The differences between IR and Raman active character of band types can give a good chance to go closer to the solution.

Thanks, László Kótai

Very interesting thoughts. I don't think my fossil were preserved in Borax. However, I never consider Boron before. Will look into this.

The 1800 cm-1 peak is most probably not from carboxylic dimer, which should rather be at 1710 cm-1.

The 2800-3000 cm-1 peaks are most probably from methyl and methylene groups.

The 2500-2700 cm-1 peaks. I have seen in literature that these might arise from a carboxylic group, but I have never seen such things myself and was never able to understand which bond might contribute to this. On the other hand, O-D bonds contribute nearby, although I do not think you have heavy water in your sample, do you?

No, I don't think these fossls, many fossils from various taphonomic environments, would contain heavy water or being soaked in. We are very puzzled by the peaks at 2500-2700 cm-1. Is that possible that D ions were absorbed and locked inside the fossils? I don't know if that is the case. Another possibility is the S-H bones. But I can't be sure on that too. Thanks Andrei.

Dear Timothy,

If you have enough sample, I would suggest doing some other studies to interpretate the IR bands. For example, a Raman, an XPS, XRD, a TGMS (TG-IR) could show what kind of materials are present or are formed during the heating. Without supplementary information, it will be very hard to define what happens.

Mr. Huang, very long time discussion. But when it is still continuing I will take part. The 2500 is nSH (This is very specifuic region for SH group). While the ca. 2900 + 1800 is very specific for R-(H)C=O of aldehyde. If you provide MS spectrum, than it cpuld be unambigously determine. But taking into account that for alkyl fragment R it has not bands, than are you sure that this is the IR-spectrum of single compoound!? Have you preliminary separation step?! Because of if 3000 cm-1 is rom aromatic CH, that the spectrum is relatively poor!? Can you provide the spectroscopic range within 1800-400 cm-1.

Thank Bojidarka. I did not have any chance to run our fossil sample with MS yet. And since these are fossils, of course couldn't be pure compound, but a mixture of many many compounds. We are trying to interpret sr-FTIR spectra of many fossils.

Mr. Huang, than most probably you have thioformic acid (H(C=O)SH). But in dimmeric form or hydrogen bonded chains. It has available literature (below 3 papers) on this matter, showing that for isolated monomer nC=O is at 1840 cm-1. In paper (1) the authors studied monomer at 20 Torr (Fig. 1). But they observed additionally bands at 3400 cm-1 and 1450 cm-1, which most probably are of nOH and nC=S stretching vibrations, meaning that at 20 Torr they most probably have H-exchange and formation of H(C=O)SH/H(C=S)OH species. Most probably you also have such process. The papers are:

(1) Winnewisser, B.; Hocking, W. J. Phys. Chem., 1980 , 84, # 14, 1771 - 1782

(2) Randhawa; R., J. Mol. Struct. 1974 , 21, p. 123,126,131-133

(3) Reisenauer, H.; Schreiner, P.; Mloston, G.; Romanski, J. J. Am. Chem. Soc. 2010 , 132, # 21, 7240 - 7241

Dear Dr. Timothy Huang,

If I understand well, where you found the fossils, that could contact with water? If it could contact with water, it is not very probably that a water-soluble organic compound as thioformic acid would be present in it - except, if that is an inclusion. Bojidarka is right, these bands really can belong to this kind of organic groups, but that is a question, that these group belong to a simple water-soluble organic compound or a part of a large insoluble molecule, e.g. a protein or likes.

If the sample could not contact with water - if you have enough sample- extractions should be done to separate the soluble and insoluble parts and study them separatedly.

I would like to help you - my son is a fond of dino's, he likes them and know them very well - but it seems to be sure, that without further studies (XRD, etc) this problem will be hard to solve.

If you could arrange some measurements in China we will help you to evaluate the result, or if someboy comes to Hungary from your university/institute, or you can send some milligramm of samples we can do some study - without destroying that (e.g. XRD, XPS) or if it is possible with destroying some milligram from that (GC-MS, GC-IR, pyrolyis-MS).

Thanks, László,

The specimen was trimmed to several hundred microns, then hand ground down with water on sand paper. Then, it was completely dried before subjected to synchrotron radiation FTIR. Along the line, we published a Nature cover paper on April 11, 2013 (Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains). We saw other evidence on the existence of complex proteins, very likely collagen type I. Nevertheless, we are working on finding out the constituents of these preserved organics.

For the detail analysis, perhaps we can discuss in private emails. [email protected]

smiles

Dear Timothy,

I don't know if You are still interested in answering this question, but I have one idea. If it's possible that you have some carbonates (like calicite or dolomite) this would be combination bands of some of thise in FTIR.. I observe them frequently in the same "configuration" when I analyse natural carbonate rocks (in most cases calcite or dolomite) . Once I found a papier with some theory for the bands it would be energetics of nanphase calcite by Tori Z. Forbes et al. there you have a the link : Article The energetics of nanophase calcite

Article The energetics of nanophase calcite

Thanks, Maja,

I'm still looking for the answer of this 'strange' ~2500 cm-1 peak. I don't know if quantum calculation can explain this as carbonates or not.

Thanks again.