1 Introduction to Spectroscopic Methods Part 1 Spectrometry: Analytical methods based on atomic and molecular spectroscopy Spectroscopy: Study of interaction between radiation (electromagnetic radiation or other forms of energy such as acoustic waves and beams of particles- ions and electrons) and matter (a branch of science).Radiation - Wave-particle duality 2 • Sinusoidal wave model • Discrete particle modelThe Electromagnetic SpectrumKinds of Spectroscopy 4 Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011What%about%E?%5 ν = c / λE = hνLIGHT Electro-magnetic radiation 67 Light as a Wave8 Light as a Wave Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 20119 Light as a Wave Frequency = ν (determined by the source)Velocity of propagation = v = νλ (depended upon composition of the medium)Speed of light in a vacuum = c = 3.00 x 108 m/s Wavenumber (reciprocal of λ) = kν Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 200710 Effect of the Medium on a Light Wave • Frequency remains the same. • Velocity and Wavelength change. Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011 λ c = νλ = 3.00 x 108 m/s11 Mathematic Description of a Wave Y = A sin(ωt + φ) A = Amplitude ω = angular frequency = 2πν = λπv2φ = phase angle Y = A sin(2πνt + φ) Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 201112 Mathematic Description of a Wave Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011 Sine waves with different amplitudes and with a phase different of 90 degree13 If two plane-polarized waves overlap in space, the resulting electromagnetic disturbance is the algebraic sum of the two waves. Superposition of Waves Y = A1sin(2πν1t + φ1) + A2sin(2πν2t + φ2) +……. 1. N electromagnetic waves can be differ in frequency, amplitude, and phage angle. 2. These waves will pass some point in space simultaneously.14 Superposition of sinusoidal wave: (a) A1 < A2, (Φ1 - Φ2) = 20º, ν1 = ν2; (b) A1 < A2, (Φ1 - Φ2) = 200º, ν1 = ν2 Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 201115 Optical Interference Constructive Interference 1) Have identical frequency 2) φ2 – φ1 = δ = ±m2πDestructive Interference 1) Have identical frequency 2) φ2 – φ1 = δ = (2m+1)πFigure 3-4 – Ingle and Crouch, Spectrochemical Analysis φ2 – φ1 = 180 deg or 180 plus an integer of multiple of 360 deg. φ2 – φ1 = 0, or 360 deg or integer of multiple of 360 deg.16 Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011 Superposition of two sinusoidal wave of different frequencies but identical amplitudes. Should be ν17 Superposition of sin waves to form a square waveElectro-magnetic radiation • Light as a wave. • Mathematic description. • Superposition of waves (interference). 18Diffraction, Refraction and Reflection 19Diffraction: The Bending of Light as It Passes Through an Aperture or Around a Small Object 20 Diffraction will be less and can be seen only at the edges. Wave will undergo the process of notable diffraction. d(x y) >> λ d(x y) = λ21 Eugene Hecht, Optics, Addison-Wesley, Reading, MA, 1998. Diffraction increases as aperture size → λDiffraction of Waves in a LiquidDiffrac0on%Pa3ern%From%Mul0ple%Slits%22 Diffraction is a consequence of interferenceDiffraction Pattern From Multiple Slits 23 Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 201124 Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011 CF = BC sin θ = nλ n is an integer called order of interference nλ=BCDEOD=BCDEOECalculations- Diffraction Pattern From Multiple SlitsCalculations 25 λ = wavelength of light used (m) x = distance from central fringe (m) d = distance between the slits (m) n = the order of the fringe L = length from the screen with slits to the viewing screen (m)Diffraction - Coherent Radiation 26 θConditions for coherent of two sources of radiation are: 1. Identical frequencies and wavelength 2. Phase relationship remains constant with time27 Eugene Hecht, Optics, Addison-Wesley, Reading, MA, 1998. Conservation Law α(λ) + ρ(λ) + T(λ) = 1 α(λ) = Fraction Absorbed ρ(λ) = Fraction Reflected T(λ) = Fraction Transmitted What happens when light hits a boundary between two media? Refraction: change in direction of radiation as it passes from one medium to another with different density Physics of RefractionRefrac0ve%index%(n)%• The velocity (v) of EM radiation depends on the medium through which it travels %%C%the%ra0o%of%the%velocity%in%vacuum%over%the%velocity%in%the%medium%(ni%>1).%• ni depends on the frequency of the light 28 ni=cvi29 Transmission: The Refractive Index Eugene Hecht, Optics, Addison-Wesley, Reading, MA, 1998. vnc =n is wavelength (frequency) dependent. In glass n increases as λ decreases. Liquids (n) : 1.3-1.8; Solids (n): 1.3 – 2.5 or higherRefrac0on%30 Snell’s Law Douglas A. Skoog, et al. Principles of Instrumental Analysis, Thomson, 2011 sinθ1sinθ2=n2n1=v2v1(n2)air=(sinθ1)airsinθ2Less dense medium More dense medium nvac=1.00027nairRefraction 31Refraction 3233 Dispersion and Prisms Dispersion The variation in refractive index of a substance with wavelength or frequency ni=cvi34 Dispersion and Prisms is most suitable for the manufacture of lenses is selected for the fabrication of prisms35 Prism A transparent optical element with flat, polished surfaces that refract light.36 A ray of single-wavelength incident on a prism θ1 θ2 θ3 δ δ: angle of deviation Cai® 2007 Prism A transparent optical element with flat, polished surfaces that refract light.37 A ray of white-wavelength incident on a prism δR δB White light Cai® 200738 A ray of white-wavelength incident on a prism Cai® 2007 Dispersive prism39 Reflection of Radiation I0: intensity of incident light Ir: reflected intensity For monochromatic light hitting a flat surface at 900 Reflected Ray (Ir) Incident Ray (Io) IrI0=(n2− n1)2(n2+ n1)2n1 n240 Ingle and Crouch, Spectrochemical Analysis ρ(λ) at different interfaces Reflectance is the fraction of the incident radiant energy reflected.41 Reflection of Radiation Specular reflection Diffuse reflection42 Reflection of Radiation Specular reflection Diffuse reflection Specular reflection: smooth