L2 Rich: ir spectroscopy part 1 Flashcards
what does IR stand for?
infrared spectroscopy
what is shot through a sample?
IR radiation
what do molecules absorb and what does this promote?
absorbs certain frequencies which leads to a higher vibrational energy level
Historically IR spectra are shown as ______
transmission
Spectra can be plotted as _________
absorption
what can IR spectroscopy be preformed on?
Solids, Liquids and Gases
what type of techniques an be used on solids?
- KBr disc
- Nujol mull
- Attenuated Total Reflection (ATR)
what type of IR be done on liquids?
- Salt plates
* Attenuated Total Reflection (ATR)
what type of IR be done on gases ?
gas cell
how does sample preparation for KBr disc work?
solid sample ground with dry KBr
placed in mould and compressed
KBR shows cold flow and forms transparent disc
what are some issues with KBr?
fragile and difficult
sample recovery difficult
does KBr absorb IR?
no
how does sample preparation for Nujol mull work?
- sample ground and dispersed in mineral oil
- mixed
thin layer spread between polish sodium chloride plates
How many absorption bands does Nujol have?
3 major bands
Possible to run in _______________ as a supplement
hexachlorobutadiene
How is sample recovery with the Nujol Mull preparation?
difficult
whats used to analyse liquids?
two dismountable IR windows
what does qualitative analysis of liquids involve?
a drop of sample compressed between two NaCl or KBr discs without spacers to create a film
can salt plates be used for aqueous samples?
no
Quantitative analysis uses cells with?
a variable or fixed path length
Absorbances for gases can be weak, this means what is needed?
a long pathlength is often needed
what is needed for IR on gas cell?
- Glass gas cell with non IR absorbing windows at each end
- Single crystals of NaCl, KBr, CaF2 or even CsI cut shape and polished
- Possible to also use balloons and gas sampling bags
why is low pressure needed when finding IR of gas cells?
to avoid interactions
start back at
ATR
