GG 711: Advanced Techniques in Geophysics and Materials Science
Spectroscopy: Lecture 2
Atomic Spectra
Anupam Misra
HIGP, University of Hawaii, Honolulu, USA
www.soest.hawaii.edu\~zinin
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)
Flame tests
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.
http://www.nasa.gov/mission_pages/messenger/multimedia/mercury_telecon_20081029.html
Emission spectra of atoms
Atomic spectra:
* Simplest atom is Hydrogen atom
Absorption spectra
Emmision spectra
* Why so many lines: it has only 1 electron ?
www.solarobserving.com/halpha.htm
Bohr’s model of atom;
Postulates:
1. Every atom consists of nucleus and
electrons revolved around the nucleus in
circular orbits.
2. Electrons revolved only in certain nonradiating 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.
De Broglie wave
p = h / λ = ħk
k = 2 π/ λ
2πr=nλ
= n h/ (mv)
mv r = n ħ
k = 1/ (4 πεo) = 9 x 109 Nm2/C2
r ∝ n2
Bohr Radius
Bohr Radius.
J
Hydrogen energy levels:
0 eV
www.physics.fsu.edu/.../images/hydrogen.gif
www.physics.udel.edu/.../images/hydrogen.gif
-13.6 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?
Bohr model: The energy of the n-th level is:
E=hν
c=λν
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)
1 eV = 1.6×10−19 Joules
h = 6.6×10−34 Joules.sec
c = 3×108 m/s = 299 792 457 m/s
* Simplest atom is Hydrogen atom
En
n = 1, 2, 3, ...., denoting energy;
K, L, M, N…for n = 1, 2, 3, 4, …
l = 0, 1, ..., n-1, denoting angular momentum;
s, p ,d , f…for l = 0, 1, 2, 3…
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).
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)
http://www.flickr.com/photos/clementi/3278124162/
formulae to remember
E=ħω =hf
ω =2πf
p=ħk =h/λ
k =2π/λ
c=fλ
E = pc (for photon)
NIST Atomic Spectra Database Lines Data
NIST Atomic Spectra Database Lines Data
NIST Atomic Spectra Database Lines Data
Homework:
Q1. Calculate the frequency and wavelength of the photon emitted when an
electron 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.
From Wikipedia: Wave vector k