Interactions Between Light & Matter

Radio waves

Wavelength: 1 m to 100+ m

- Responsible for AM & FM radio
- Excited spin of nucleus – used in MRI (noninvasive)

Microwaves

Wavelength: 100 𝜇m to 1 m

- Causes molecules to rotate
- Around 12 cm rotates H2O and fat molecules to heat food
- Excited spin of electrons

Infrared

Wavelength: 800 nm to 100 𝜇m

- Causes molecules to vibrate
- Used in night vision goggles
- Excited bond for OH in ethanol – used to measure intoxication

Visible

Wavelength: 400 nm to 800 nm

- These are the rays human eyes can detect
- Used for the solution of the H atom
- Excites e− to higher energy levels

Ultraviolet

Wavelength: 0 nm to 400 nm

- Causes sun burns
- Lyman series for H emission (n = 1)
- Excites valence e−

X-rays

Wavelength: 0.01 nm to 10 nm

- Causes cell mutations, so limit exposure
- Used in medicine for invasive imaging
- Excites core e^-

γ-rays = gamma rays = cosmic rays

Wavelength: < 0.01 nm

- Emitted from stars, hence the name “cosmic rays”
- Associated with the decay of an atom’s nucleus