An introduction to Spectrometric Methods

Spectroscopy Definition Spectroscopy is a general term for the science that deal with the interactions of various types of radiation with matter. Historically the interactions of interest were between electromagnetic radiation and matter, but now spectroscopy has been broadened to include interactions between matter and other forms of energy For examples acoustic waves and beam of electrons or photons.

General Properties of Electromagnetic Radiation Wavelength Amplitude Time or Distance Electric Field

Gama X-ray UV Radio IR Visible Microwave Frequency (Hz) Wavelength (m) Regions of the electromagnetic spectrum

Mathematical description of a wave y = A sin (  t+  )  =2  y = A sin (2  t+  )

Superposition of Waves The principle of Superposition: When two or more waves traverse the same space, a disturbance occurs that is the sum of the disturbances caused by individual waves y = A 1 sin (2  1 t+  1 ) + A 2 sin (2  2 t+  2 ) + A 3 sin (2  3 t+  3 ) + …. + A n sin (2  n t+  n )

Superposition of Waves Constructive Interference Destructive Interference

Superposition of Waves  A =A + A

Superposition of Waves Square Wave

xy >> xy = x y x y Diffraction of Radiation

Young’s Experiment

Coherent radiation Conditions for coherence –Two sources of radiation must have identical frequencies ( or sets of frequencies) –Phase relationships between two beams must remain constant Coherent sources –Radio frequency oscillators –Microwave sources –Optical lasers Random source –Tungsten filament lamp

Transmission of Radiation The rate at which radiation is propagated through a transparent substance is less than its velocity in a vacuum and depends on the kinds and concentration of atoms, ions, or molecules in a medium.  i   c / v i

Anamalous dispersion Normal dispersion Infrared Ultraviolet Frequency Hz Refractive index Dispersion of Radiation Normal dispersion The variation in refractive index of a substance with wavelength or frequency is called dispersion.

 22 Refraction of Radiation M1M1 M2M2

Reflection of Radiation I 0 Intensity of incident beam I r Intensity of reflected beam For beam that enters an interface at right angles

Scattering of Radiation Rayleigh Scattering –Scattering by molecules or aggregates smaller than the wavelength of radiation. Scattering by large molecules –By colloidal particles Raman scattering

Polarization of Radiation Unpolarized end-on view Plane polarized end-on view Monochromatic radiation Electrical vectors of a beam Resolution of a vector Resultant of all vectors

Energy States of Chemical Species Electronic Vibrational Rotational

Excitation Sources: 1- Electron bombardment 2- Electrical Arc or Spark 3- Flame 4- Furnace 5- Electromagnetic radiation 6- Photochemical Reactions Emission of Radiation

Emission Spectrum Na 330.2, K , Ca Na 466.5, Na CaOH 544 Line MgOH Band Continuum Wavelength nm Re;ative power P

Energy level diagram for Na E0E0 E1E1 E2E2 Electronic Energy levels Excitation Emission 330 nm s Emission 590 nm

X-Ray emission spectrum of Mo Wavelength A Relative Power P X-ray emission spectra do not depend on the media

Energy level diagram for a simple molecule E0E0 E1E1 E2E2 Vibrational levels

Continuum Spectra Black body radiation curves Wavelength nm Xenon arc Carbon arc Tungsten lamp Nernst glower 6000 o K 4000 o K 3000 o K 2000 o K

Absorption of Radiation Atomic Molecular Induced by a magnetic field

Molecular Absorption E0E0 E1E1 E2E2

Ultraviolet absorption spectra Wavelength nm Na vapor Benzene vapor Benzene in hexane Biphenyl in hexane Absorbance

Relaxation Processes Nonradiative Fluorescence and phophorescence

Nonradiative Relaxation E0E0 E1E1 E2E2

Fluorescence and Phophorescence E0E0 E1E1 E2E2

General Properties of Electromagnetic Radiation Wave –W–Wavelength –F–Frequency –V–Velocity Particle

Wave Properties Electric field Magnetic field Monochromatic plane polarized radiation Wavelength Amplitude

Wave Properties Amplitude is the maximum length of electric field vector. Period is the time in seconds required for the passage of successive maxima through a fixed point. Frequency is the number of oscillations of the field occuring per second. Wavelength is the distant between any two equivalent points on the wave.

Wave Properties v i = i v is velocity of propagation Air Glass Air  = 500nm  =330nm  = 500nm = 6*10 14 Hz  = 6*10 14 Hz = 6*10 14 Hz

Regions of Electromagnetic Spectrum X-ray Visble Microwave Gamma ray Ultraviolet Infrared Radio Hz m

Wavenumber is reciprocal of wavelength in cm. Power of radiation is the energy of the beam that reaches an area per second.

Superposition of Waves A < A  –  = - 20 = = +

Superposition of Waves A < A  –  = = = +