Instrumental Analysis

Introduction to Spectroscopic Methods
• Spectroscopy: general term for the science that deals with interaction of various types of radiation with matter

1.Atomic Spectroscopy 2.Molecular spectroscopy
• Important to understand the interaction between the electromagnetic radiation and the matter (mainly), + interaction of a acoustic waves and beam of particles (ions, electrons) with matter.

• Wave model failed to account for absorption and emission of EM energy
– (sinosoidal wave model (λ , f, v, Amplitude)

• Particle model : EM radiation is viewed as stream of discrete particles or wave packets, of energy called Photons where energy is proportional to frequency ( )

E~ f

Electromagnetic Radiation
• Electric field- responsible for most phenomena
(transmission reflection, refraction and absorption)

• Magnetic field responsible for absorption of RF waves in NMR

Wave Properties of EM Radiation
• Velocity, c = 3.0 × 108 m/s (vacuum) • Wavelength, λ characterizes type of radiation, units of length (e.g., nm for Vis and UV, Aº for Xray) 1 • Wavenumber υ = , cm-1 λ • Frequency, ν = c/λ, measured in s–1 (Hz) • Frequency of a particular light wave is invariant (fixed by the source); c varies with refractive index of medium λ also depends on medium • Velocity of EM in a medium slows down due to interaction of EM with bound electrons in the matter

Electromagnetic Spectrum

• Energy of light, E = hν = h λ = h c ν • Planck’s constant = 6.63 × 10-34 J s

c

Spectrum of Electromagnetic Radiation
Electromagnetic radiation is light. Different energy of light can interact with different energetics in matter. Radiofrequency (3cm-10m) MHz Microwave (0.75-3.75mm) GHz Nuclear spin Electron spin Molecular rotation Infrared (.78-300µm) THz Molecular vibration Vibrations in solids UV/Visible (180-780nm) PHz Electronic transitions (valence shell) Far UV/X-ray (.1-100 Aº) PHz Electronic transitions (core shells) Gamma ray (.005-1.4 Aº) EHz Nuclear transitions Mössbauer Spec. UV/X-ray Spec. UV/Vis Spec. NMR ESR (EPR) Microwave Spec. IR Spec.

Various phenomena of EM Radiation
• Wave description explains certain EM radiation phenomena: – Transmission: does not involve permanent energy transfer
(momentary retention of energy by molecules or atoms then reemission) c Refractive index

ηi =

– reflection and refraction: Change in direction when passing from one – – – medium with an angle to another Diffraction: Parallel beam of radiation is bent as it passes by a sharp barrier or through a narrow opening Interference: superposition of waves Scattering: transmission of radiation at all angles from the original path • Rayleigh scattering: elastic scattering by very small particles (d