I know that FTIR spectroscopy is usually used to detect the vibrational characteristics of molecular bonds (bending, stretching, etc.) in the IR region. I also know that, for water, information about hydrogen bonding can be determined based on how these bending/stretching vibrations are shifted/modified (e.g., image attached, from J. Chem. Phys. 134, 164502 (2011)).
Besides this, I would like to know if FTIR can be used to detect hydrogen bonds directly, as opposed to sensing them based on modifications to other bonds. From my understanding, hydrogen bond strengths in water may vary in the range of about 1800 cm-1 (e.g., liquid water) down to roughly 1000 cm-1 (e.g., for water dimers or other clusters in the vapor state).
I assumed incoming radiation matching the bond strength could be absorbed and break/dissociate the H-bond, in which case an absorbance peak would be visible. But I haven't found any work in the literature that does this, so I assume it's not valid. If the H-bond energies are in the IR range, why can't FTIR be used to detect them?
Thanks!
Andrew
Well, that's the point about normal modes of vibrations: there may be occasions in which you are lucky and they are highly localized like a C=O stretching vibration in an organic molecule, but generally that is not the case and a vibration is happening in a larger collective entity. That is the case for quite a lot of phenomena in water. An expert in this field would be Martina Havenith-Neven, so check out the publications of her group and maybe even contact them:
https://www.ruhr-uni-bochum.de/pc2/publikationen.html.en
- Badges
- Science topic