ACCTG 1 Lecture Notes - Lecture 2: Hexachlorobutadiene, Mull, Evanescent Field
Document Summary
Absorption of energy promotes molecules to higher vibrational energy levels. Liquids: salt plates, liquids analysed using 2 dismountable ir windows, qualitative analysis uses a drop of sample compressed between two. Nacl or kbr discs without spacers to create a film: cannot be used for aqueous samples, quantitative analysis uses cells with a variable or fixed path length, path length must be calibrated, attenuated total reflection (atr) Gases: gas cell, absorbances for gases can be weak so a long pathlength is often needed, glass gas cell with non ir absorbing windows at each end, single crystals of nacl. Kbr, caf2 or even csi cut to shape and polished: low pressure used to avoid interactions, possible to also use balloons and gas sampling bags. Crystal made of diamond, germanium, zns, thbr or znse with a high ri. Combination of high ri and geometry cause a series of internal reflections, referred to as an evanescent wave.
