University12 min

IR and UV-visible: reading a spectrum, quantifying with Beer-Lambert

The IR bands to spot at a glance, a routine for reading a spectrum from left to right, and the Beer-Lambert law without unit mistakes.

The essentials

1

Photon and wavenumber

E=hν=hcλν~=1λE = h\nu = \frac{hc}{\lambda} \qquad \tilde{\nu} = \frac{1}{\lambda} The wavenumber ν~\tilde{\nu}, in cm−1\text{cm}^{-1}, is proportional to energy. Conversion: ν~ (cm−1)=107λ (nm)\tilde{\nu}\ (\text{cm}^{-1}) = \dfrac{10^7}{\lambda\ (\text{nm})}. IR, from 400400 to 4000 cm−14000\ \text{cm}^{-1}: vibrations. UV-visible, from 200200 to 800 nm800\ \text{nm}: electronic transitions.
2

Vibrational modes and the selection rule

Members only

3

The landmark IR bands

Members only

4

UV-visible transitions

Members only

5

The Beer-Lambert law

Members only

ƒWrite my own sheetOr start from a blank page: rewriting a concept in your own words is how it sticks.