spectroscopy: lecture 2zinin/images/lectures/gg711... · atomic spectra • absorption spectroscopy...
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Anupam MisraHIGP, University of Hawaii, Honolulu, USA
Spectroscopy: Lecture 2
Atomic Spectra
www.soest.hawaii.edu\~zinin
GG 711: Advanced Techniques in Geophysics and Materials Science
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Atomic Spectra
• Absorption spectroscopy (UV-VIS, IR, Fraunhofer lines, atmospheric studies,..)
• Emission spectra(Calibration lamps Ne, Hg, flames, explosion, sun, stars, LIBS: Laser induced breakdown spectroscopy)
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Flame tests
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http://www.nasa.gov/mission_pages/messenger/multimedia/mercury_telecon_20081029.html
Example sodium and calcium emissions detected by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on the MESSENGER spacecraft during the second Mercury flyby.
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Emission spectra of atoms
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Atomic spectra:
* Why so many lines: it has only 1 electron ?
* Simplest atom is Hydrogen atom
www.solarobserving.com/halpha.htm
Absorption spectra
Emmision spectra
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Bohr’s model of atom;
1. Every atom consists of nucleus and electrons revolved around the nucleus in circular orbits.
2. Electrons revolved only in certain non-radiating orbits called stationery orbits for which the total angular momentum is an integral multiple of h/2π where h is plank's constant.
L is the Angular momentum of the revolving electrons.
L = r x p = r x mV
= mvr sin 90 = mvr = n h/2π
3. Radiation occurs when an electron jumps from one permitted orbit to another. It is emitted when electron jumps from higher orbit to a lower orbit
i.e., E2 - E1 = hf, where f is frequency of radiation.
Postulates:
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De Broglie wave
2 π r = n λ
= n h/ (mv)
mv r = n ħ
p = h / λ = ħk k = 2 π/ λ
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k = 1/ (4 πεo) = 9 x 109 Nm2/C2
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Bohr Radius
r ∝ n2
Bohr Radius.
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J
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www.physics.udel.edu/.../images/hydrogen.gif
www.physics.fsu.edu/.../images/hydrogen.gif
Hydrogen energy levels:
-13.6 eV
0 eV
Q 1: Line C observed at 656.3 nm in Fraunhofer lines correspond to Hydrogen. Identify this transition.Q 2. Can we see the Lyman series transition n = 2 to n = 1 with our eye?
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1 eV = 1.6×10−19 Joulesh = 6.6×10−34 Joules.secc = 3×108 m/s = 299 792 457 m/s
E = h νc = λ ν
Photon energy E, frequency ν, wavelength λ,
532 nm (green light) corresponds to 2.33 eV.
1 eV corresponds to 1240 nm (infra red)
13.6 eV would corresponds to 91 nm (deep UV)
Bohr model: The energy of the n-th level is:
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* Simplest atom is Hydrogen atom
En
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n = 1, 2, 3, ...., denoting energy;
l = 0, 1, ..., n-1, denoting angular momentum;
m = -l, ...., l, denoting orientation (the "magnetic quantum number"),
s = -1/2, 1/2, denoting spin (m s is also used in place of s).
s, p ,d , f…for l = 0, 1, 2, 3…
K, L, M, N…for n = 1, 2, 3, 4, …
Kα line is transition from n = 2 to n = 1 (L to K level)Kβ line is transition from n = 3 to n = 1 (M to K level)
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http://www.flickr.com/photos/clementi/3278124162/
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E = ħ ω = h f
formulae to remember
p = ħ k = h / λ
c = f λ E = pc (for photon)
ω = 2 π f
k = 2 π / λ
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NIST Atomic Spectra Database Lines Data
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NIST Atomic Spectra Database Lines Data
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NIST Atomic Spectra Database Lines Data
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Homework:
Q1. Calculate the frequency and wavelength of the photon emitted when anelectron of 20 keV is brought to rest in one collision with a heavy nucleus.(x-ray production).
Q2. Find the maximum wavelength of the photon that will separate a molecule whose binding energy is 15 eV.
Q3. A 93.1 MHz radio station of 200 kW output generates how many photons in 1 minute?
Q4. Find the energy and wavelength of two photons that are produced when annihilation occurs between an electron and positron that are initially at rest.
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From Wikipedia: Wave vector k