CHEM 3500 / Atomic Spectroscopy

What even is spectroscopy?

We measure the intensity of radiation that a sample emits or absorbs, as a function of energy. Plot intensity (y-axis) vs. energy (x-axis), and you get a spectrum.

What are the four parts that a spectrometer has?

Excitation → Energy selector → Sample Interference → Detector, e.g.

Tungsten lamp → grating monochromator → cuvette holder → photodiode

What is EM radiation? What are the two relationships you need to know?

Coupled oscillation of electric and magnetic field, moving @ the |v(t)| of light.

c = Hz × λ, thus if Hz ↑ → λ ↓

E = h × Hz

Which radiation does what?

• Radio (E+3) = nuclear and e⁻ spin transitions

• Microwave (E-2) → IR = rotations (↓ Hz) → vibrations (↑ Hz)

• Visible, UV (E-6 to E-8): valence e⁻ transitions

• X-rays (E-10): core e⁻ transitions

• Gamma rays (E-12): nuclear transitions

What’s the numerical value of |v(t)| of light? How about Planck’s constant?

c = 2.998E+8 m/s; h = 6.626E-34

What does each type of particle radiation do to matter? (“beam-hitting”)

• e⁻ radiation → valence e⁻ transitions to the continuum (no longer bound to the nucleus—it has become a free particle with arbitrary kinetic energy) and core e⁻ transition (either → continuum / still within atom)

• Neutron radiation → inelastic scattering: atomic motion, vibration, electronic transitions

• Muon radiation → ionization & e⁻ scattering and capture

What’s the difference between elastic and inelastic scattering?

• Elastic → no energy transfer → only direction changes

• Inelastic → energy transferred to/from the scatterer (sample)

How does inelastic neutron scattering give information about a sample?

> Neutron hits sample → bounces off with ↓ / ↑ energy

> Energy difference → goes into the sample as: atomic motion, vibration, electronic transitions.

Measure the neutron’s energy ∆ → learn about the sample’s motions/transitions.

What are Stokes and anti-Stoke scattering in Raman?

> Raman: umbrella → stokes and anti-Stokes are its two flavours

> Stokes → photon loses energy to the molecule → comes out with ↓ Hz

> Anti-stokes → photon gains energy from an already-vibrating molecule → scattered Hz ↑

> Energy shift = molecule’s vibrational Hz

What is a muon?

> Muon = “heavy electron”

> Charge = −1 = same as e^-

> Sources → particle accelerators + cosmic rays