Dear colleagues,
During my Raman work on very carbonate-rich fluid inclusions in quartz (15.8 equivalent % Na2CO3) I found beside the carbonate band at 1380 cm-1 a strong band at 1352 cm-1. The measuring is reproducible. The area ratio is about 1 : 2. According to Kazuo Nakamoto (1986) this band corresponds to [H-CO2]- and according to table VI in Ito and Bernstein (1956) to n2 C-O stretching of the formate ion.
However the formation of formate ion under magmatic-postmagmatic conditions is unlikely. So my questins: Does anybody have an idea? Is there the possibility that it is here the C2O52-ion, discussed by Zeller et al. (2005) or Claes et al. (1999)?
I would be pleased about indications for the enlightenment of this puzzle.
Best regards,
Rainer Thomas
Main components/elements are H, Na, C, O, and B (as 2.4 % H3BO3) and 0.13 mol/l HCO3-.
Mr. Thomas,
This which you have provided as Raman spectrum in your positing, among the discussed possibilities is rather HCO3-. The mode at 1380 cm-1 should belong to nsCO2, 2hile this one at 1350 cm-1 to dCOH. Despite the fact that the frequency positions are perturbed on the one hand from the typical position for alkali metal HCO3- salts. On the other hand the D(ni) difference of the shown bands in HCO3- is about 50 cm-1. In your cases however this value is only 30 cm-1.
To verify this information please check the region 1700 - 1500, where you should observe a mode about 1630 cm-1 (nasCO2) along with a mode about 650 cm-1, where you should have dCOH if the form is HCO3-
If you have those modes available, here lie the question is there possible your sample to contain non-alkali metal ions. Because of the deviation from D(ni) mentioned above can be observed when you have monodentately bonded (but not to alkali metal ions) HCO3- ligand, thus forming M-O-(C=O)OH coordination compound.
Definitively you have not isolated CO32- dianion, because of ni3 mode (single mode) is at 1440 cm-1 (Au+Bu(TO), C3v symmetry). This mode could be shifted towards low frequencies (up to 1380 cm-1, for example), like in the shown spectrum, but this means again coordination to non-alkali metal ion, furthermore fully symmetric, thus keeping C3v* symmetry of the ion, when we have one active Raman mode. Or there is possible the observations of two bands like in your case, but this means again that you have non-symmetric coordination, and again with non-alkali metal ions.
Despite this, please check at 1080 cm-1, have you mode or not?! Because of for CO32- you should have a mode relatively strong intensive in the Raman spectrum for ni1 (Au(TO)) in the same ionic symmetry. Please check as well as have you ni2 mode about 850 cm-1 and corresponding overtone at position 2x(ni2).
To confirm presence of pyrocarbonates, there is important to check as well as, not the shown in your attachment region. Those species due to the vibrational interactions typical for anhydrides should have pair of modes about 1840+1740 cm-1 and a single mode about 1450 cm-1, due to the high symmetry of the pyrocarbonate dianion. Please bear in mind that if you have coordinated to non-alkali metal ion C2O52-, the pair of modes at 1840+1740 cm-1 remains, furthermore the difference D(ni) between both the frequencies (about 100 cm-1) is also weakly affected.
In other words, the observation of two bands in the discussed regions indicates rather low symmetry of the anion, meaning HCO3- (Cs) or asymmetric coordinated CO32- to non-alkali metal ions, rather than high symmetry species such as isolated (CO32-, C3v*) and pyrocarbonate dianion (C2v*).
Can you upload the Raman spectrum within, for example, 1800-600 cm-1 along with information have you only alkali metal ions?
Dear Bojidarka B. Ivanova,
Many thanks for the information and suggestions. I will carry out further studies. After those I report again.
Best regards,
Rainer Thomas
Dear Bojidarka B. Ivanova,
I have checked the region between 820 and 1250 cm-1: there is a strong band at 1080.4 cm-1, however influenced by the quartz matrix; the 850 cm-1 mode is completely missing. The HCO3- band at 1017 cm-1 is present and corresponds to about 0.15 mol HCO3-, the band at 1352 cm-1 would, however, yield 0.65 mol HCO3-. The height and the position of this band astonishes me. Because of the homogeneity of the solution in the inclusion (solution + small CO2-bubble) other no non-alkali metal ions in significant amounts are unlikely.
Unfortunately, I can carry out clearing studies only in the new year.
Thanks for your explanations and hints.
A Merry Christmas and Happy New Year,
Rainer Thomas
http://www.geochem.geos.vt.edu/fluids/projects.shtml
http://sps.esd.ornl.gov/facilitiestools.html
Here are a couple of links about CO2 inclusions
Hello Peter Anthony Tanner,
Many thanks for your efforts. However, your notes have nothing to do with the real problem!
Best regards,
Rainer Thomas
Enclosed you find the Raman spectrum of the fluid inclusion in quartz in the 600 – 1800 cm-1 range. Note that one gets considerably different concentrations from the integral intensity of the HCO3- bands at about 1017 and 1353 cm-1 (factor over 3). For saturated NaHCO3 solutions this factor is 1.
Non-alkali metal ions cannot be present (homogeneous solution!). The only possibility would be beryllium, because I have found in (maybe) syngenetic fluid inclusions daughter crystals of hambergite [Be2BO3(OH,F)], demonstrating high concentrations of Be. However little is known about the Raman spectra of such carbonate/hydroxide species of beryllium.
Could it possibly be a combination band? Did you record spectra below 600 cm-1 maybe?
Attached is the Raman spectrum in the range 85-1200 cm-1. This spectrum does not show any deviations on other carbonate/bicarbonate-bearing samples.
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