FIU CHM 4130 - CHAPTER 6A_Xiao_Introduction_to_Spectroscopy_2018 (1) (52 pages)

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CHAPTER 6A_Xiao_Introduction_to_Spectroscopy_2018 (1)



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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 1 Radiation Wave particle duality Sinusoidal wave model Discrete particle model 2 The Electromagnetic Spectrum Kinds of Spectroscopy Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 4 What about E E h c 5 LIGHT Electro magnetic radiation 6 Light as a Wave 7 Light as a Wave Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 8 Light as a Wave Frequency determined by the source Velocity of propagation v depended upon composition of the medium Speed of light in a vacuum c 3 00 x 108 m s Wavenumber reciprocal of k Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2007 9 Effect of the Medium on a Light Wave Frequency remains the same Velocity and Wavelength change c 3 00 x 108 m s Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 10 Mathematic Description of a Wave Y A sin t A Amplitude phase angle 2 v angular frequency 2 Y A sin 2 t Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 11 Mathematic Description of a Wave Sine waves with different amplitudes and with a phase different of 90 degree Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 12 Superposition of Waves If two plane polarized waves overlap in space the resulting electromagnetic disturbance is the algebraic sum of the two waves Y A1sin 2 1t 1 A2sin 2 2t 2 1 N electromagnetic waves can be differ in frequency amplitude and phage angle 2 These waves will pass some point in space simultaneously 13 Superposition of sinusoidal wave a A1 A2 1 2 20 1 2 b A1 A2 1 2 200 1 2 Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 14 Optical Interference Constructive Interference 1 Have identical frequency 2 2 1 m2 2 1 0 or 360 deg or integer of multiple of 360 deg Destructive Interference 1 Have identical frequency 2 2 1 2m 1 2 1 180 deg or 180 plus an integer of multiple of 360 deg Figure 3 4 Ingle and Crouch Spectrochemical Analysis 15 Should be Superposition of two sinusoidal wave of different frequencies but identical amplitudes Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 16 Superposition of sin waves to form a square wave 17 Electro magnetic radiation Light as a wave Mathematic description Superposition of waves interference 18 Diffraction Refraction and Reflection 19 Diffraction The Bending of Light as It Passes Through an Aperture or Around a Small Object Diffraction will be less and can be seen only at the edges d x y Wave will undergo the process of notable diffraction d x y 20 Diffraction of Waves in a Liquid Diffraction increases as aperture size Eugene Hecht Optics Addison Wesley Reading MA 1998 21 Di rac0on Pa3ern From Mul0ple Slits Diffraction is a consequence of interference 22 Diffraction Pattern From Multiple Slits Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 23 Calculations Diffraction Pattern From Multiple Slits CF BC sin n n is an integer called order of interference n BCDE BCDE OD OE Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 24 Calculations 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 25 Diffraction Coherent Radiation Conditions for coherent of two of radiation are sources 1 Identical frequencies and wavelength 2 Phase relationship remains constant with time 26 Physics of Refraction 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 Conservation Law T 1 Fraction Absorbed Fraction Reflected T Fraction Transmitted Eugene Hecht Optics Addison Wesley Reading MA 1998 27 Refrac0ve index n The velocity v of EM radiation depends on the medium through which it travels c ni vi the ra0o of the velocity in vacuum over the velocity in the medium ni 1 ni depends on the frequency of the light 28 Transmission The Refractive Index c n v n is wavelength frequency dependent In glass n increases as decreases Liquids n 1 3 1 8 Solids n 1 3 2 5 or higher Eugene Hecht Optics Addison Wesley Reading MA 1998 29 Refrac0on Snell s Law Less dense medium sin 1 n2 v2 sin 2 n1 v1 More dense medium sin 1 air n2 air sin 2 nvac 1 00027nair Douglas A Skoog et al Principles of Instrumental Analysis Thomson 2011 30 Refraction 31 Refraction 32 Dispersion and Prisms c ni vi Dispersion The variation in refractive index of a substance with wavelength or frequency 33 Dispersion and Prisms is most suitable for the manufacture of lenses is selected for the fabrication of prisms 34 Prism A transparent optical element with flat polished surfaces that refract light 35 Prism A transparent optical element with flat polished surfaces that refract light A ray of single wavelength incident on a prism 1 2 3 angle of deviation Cai 2007 36 A ray of white wavelength incident on a prism R B White light Cai 2007 37 Dispersive prism A ray of white wavelength incident on a prism Cai 2007 38 Reflection of Radiation Incident Ray Io Reflected Ray Ir For monochromatic light hitting a flat surface at 900 2 n1 I r n2 n1 2 I 0 n2 n1 n2 I0 intensity of incident light Ir reflected intensity 39 at different interfaces Reflectance is the fraction of the incident radiant energy reflected Ingle and Crouch Spectrochemical Analysis 40 Reflection of Radiation Specular reflection Diffuse reflection 41 Reflection of Radiation Specular reflection Diffuse reflection Specular reflection smooth surface light reflected at a definite angle Diffuse reflection rough surface reflect light in all direction 42 A beam of light diffuses on a rough surface 43 Application of Specular and Diffuse Reflection A dry asphalt roadway diffuses incident light When wet water fills in the crevices resulting in specular reflection and a glare 44 Scattering of Radiation Very small fraction of radiation transmitted at all angles from its original path The intensity increases with particle size Rayleigh sca ering Mie sca ering Raman Sca ering 45 Rayleigh scattering Size of molecule wavelength Dimension of molecules or aggregates of molecules


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