Starting with the end of the 50ies of the last century, it was assumed that determining not only the band positions, but also intensities would be a big step forward for infrared spectroscopy. Why do you think has this revolution never happened?
Thomas,
What discoveries did they think knowing the band positions and their intensities would lead to?
A lot of that information is now available in the HITRAN database: Gordon, I. E., et al. (2017) ‘The HITRAN2016 molecular spectroscopic database’, Journal of Quantitative Spectroscopy and Radiative Transfer [Online]. DOI: 10.1016/j.jqsrt.2017.06.038 (Accessed 14 September 2017).
Dear Alastair,
thanks! I would not expect any new discovery. The idea behind intensity is a rather old one. E.g. it was found that for different compounds with the same structural unit, this unit can have very similar oscillator positions, but very different intensities (=oscillator strengths).
I for myself would go even one step further and not only determine position and strengths, but also the damping constants. With all those parameters in your hand, you can:
→ Correlate optical properties and structure → Establish the connection to quantum mechanical calculations → Reduce the spectral data drastically
Actually, this means that you have determined the full dielectric function (tensor). With that you have the possibility for
→ the calculation of reflectance, absorption/absorbance, transmittance, scattering for arbitrary structures → providing input for computational photonics (FDTD etc.) to understand e.g. SEIRA
→ use the data for remote sensing of objects in space
Hitran is a nice start, as are astronomical databases. Overall, this means that we have data for roughly 0.001 % of all known compounds...
What do you mean that band intensity is not used? What is the context?
Infrared peak absorption intensity is used routinely in many areas of sciences.
Are you speaking about molar absorptivity values of different molecular bonds?
They are highly sensitive to conformation, environment, physicochemical conditions (temperature, pressure, stress..), molecular interactions so are hard to determine, measure and use accurately. But you find approximations for many systems.
Peak Intensity (and, also, the negativ decadic logarithm of it) is of course a useless quantity and this is also valid vor molar attenuation constants, because they are no specific values since Beer's law is in many right from the start only approximately correct which you see when you derive it from Electromagnetic theory. I would go for oscillator strengths (see e.g.Article Quantitative Evaluation of Infrared Absorbance Spectra – Lor...
) as I mentioned above. And yes, I guess what you want to exploit is exactly their high sensitiveness with regard to confirmation and molecular interactions. I think this is what the guys 70 years ago had in mind. You "just" have to separate all other influences and also the optical ones from those. Instruments (equipment and spectral evaluation procedures) exist, so why not go for it?
Dear dr. Thomas Mayerhöfer
Good discussion
Best regards
Dear Dr. Krzysztof Beć
Best contributions
Best Regards
Article The Modern Revolution in Infrared Spectroscopy
https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-82-5178
Article Computers and infrared spectroscopy: evolution and revolution
https://www.intechopen.com/books/infrared-spectroscopy-principles-advances-and-applications/introductory-chapter-infrared-spectroscopy-a-synopsis-of-the-fundamentals-and-applications
We have compiled a collection of answers to the question why it seems to be so problematic to determine the intensities in infrared spectroscopy in form of a review: Article The Bouguer‐Beer‐Lambert Law: Shining Light on the Obscure
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