An absorption line is a line which corresponds to the absorption of electromagnetic radiation at a specific wavelength.

In the absorption spectrum the peaks are due to preferential absorption at a definite wavelength by molecules, ions, etc.

To determine UV-absorption you need to use UV-light. And there's a defined wavelength for UV-light.

The behaviour of electromagnetic waves of depends on their wavelengths. As a result the critical angle for refraction changes according to the wavelength.

97.26 nm