# 10.3: Electromagnetic Spectrum

Most organic spectroscopy uses electromagnetic energy, or radiation, as the physical stimulus.

Electromagnetic energy (such as visible light) has no detectable mass component. In other words, it can be referred to as “pure energy.”

Other types of radiation such as alpha rays, which consist of helium nuclei, have a detectable mass component and therefore cannot be categorized as electromagnetic energy.

The important parameters associated with electromagnetic radiation are:

• Energy (E): Energy is directly proportional to frequency, and inversely proportional to wavelength, as indicated by the equation below.

• Frequency (μ)

• Wavelength (λ)

$$E = h \mu$$

### EFFECT OF ELECTROMAGNETIC RADIATION ON MOLECULES

Infrared radiation is largely thermal energy. It induces stronger molecular vibrations in covalent bonds, which can be viewed as springs holding together two masses, or atoms.

Specific bonds respond to (absorb) specific frequencies