I am doing quantitative work on carbonyl compounds dissolved in dichloromethane (DCM). I've noticed that on an ATR spectra of DCM that barely any peaks can be seen in the 1500cm-1 to 4000cm-1 range. However, when i switch to using a 3mm KBr transmission cell, many sharp peaks appear in the DCM spectra in the previously mentioned range. Why are these peaks here? Do these "ghost" peaks appear due to the concentration and pathlength being too high?
Hello,
Would you like to upload both spectrum?
KBr salt can absorb CO2 in gas phase,.(O=C=O)
What kind of corbonyl compound did you analysis ?
Dichloromethane should have only a few fundamental modes when the path length is small. ATR, depending on the crystal material used and the frequency range, samples somewhere in the vicinity of 1 - 20 micrometer thick. On the other hand, your transmission cell, being 3 mm (or 3000 micrometers) emphasizes peak intensity by the factor of hundreds to thousands. With this much intensification, weak signals, such as overtone and combination bands that arise from the finger print regions will be visible. If they are overtones or combination bands, you can double the fundamental mode, or add the frequencies of two bands, you will see rather good agreement with the new bands you observed.
I agree with Hatsuo Ishida's opinion. In transmission 3 mm is a long path and overtones of bands are very strong in this region, Pietro
- Badges
- Science topic
- Similar topics
- Physics
- Condensed Matter Physics
- Solid State Physics
- PEAKS