# Calculating the frequency of the fundamental vibrational mode

Can you calculate the frequency at which a bond vibrates when you know what frequencies of EM radiation it absorbs? Using carbon monoxide as an example. It has a stretching frequency at around 2100 cm-1. In electron volts, that would be around 0.3 eV. If I'm not mistaken, this is the energy it absorbs to jump from n=0 to n=1 (or is it n=1 to n=2?). Anyhow, if its the former then ΔE = $\frac{3}{2} - \frac{1}{2}hf$ = hf.

I know that the equation to calculate the energy of vibrational normal modes is $E_n=hf(n + \frac{1}{2})$ so wouldn't that mean that the energy of the n=0 mode is equal to $\frac{0.3 eV}{2}$?

Simon Bridge
Homework Helper
That's certainly what it means.
The classical picture is that this is the frequency of the fundamental at which the two atoms vibrate towards each other.