PHY122 – Physics for the Life Sciences II
Lecture 23
Atomic and Molecular Physics
Note: Clicker Channel 21
11/29/2011
Lecture 23
1
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Summary Quantum Physics
Photons:
–
light QUANTA with energy
E=hf=hc
/
λ
, with
hc=
1240 eV·nm
–
proof: from the
Photoelectric Effect
(sub)Atomic particles exhibit
wave character
:
– momentum
wavelength:
p=h
/
λ
–
the particle system has an associated
wave function
ψ
(r)
–
wave function squared

ψ
(r)
2
describes the
probability for finding a
particle at position
r
.
consequences:
–
monoenergetic light ánd particle beams both exhibit
INTERFERENCE and diffraction …
–
Thus: when
CONFINED
(e.g. in box of length
L
), the system shows
DISCRETE
energy/momentum levels
•
e.g. for particle in a box:
E
n
=n
2
h
2
/(8
mL
2
)
•
transitions between energy states
via emission and absorption of photons
of energy equal to the
energy level difference
•
going from the quantum to the classical regime:
n
→
large
11/29/2011
Lecture 23
2