Chapter 4: Spectroscopy
Transcript Chapter 4: Spectroscopy
The Birth of the Quantum
• Max Planck
– The energy contained in radiation is related to
the frequency of the radiation by the
• n is a positive integer called the quantum number
• f is the frequency of the oscillation
– A discreet packet of energy, later to become
known as “a photon”
Implications of Planck’s Law
• The energy levels of
the molecules must be
• Only transitions by an
amount E=hf are
• The implication is that
light is discreet or
These quantum levels are
known as number states
Three Types of Spectra
Spectral Analysis of the Elements
Studying the light emitted by an object
in order to know something about that object!
Continuous Spectrum: a collection all possible
wavelengths/ frequencies of light
Pattern of bright spectral lines
produced by an element.
Pattern of dark spectral lines
where light within a number of
narrow frequency ranges has been
Bright Line Emission Spectra
• 1st law: A luminous solid or
liquid, or a sufficiently dense
gas, emits light of all
wavelengths and produces a
continuous spectrum of
• 2nd law: A low-density hot
gas emits light whose
spectrum consists of a series
of bright emission lines which
are characteristic of the
chemical composition of the
• 3rd law: A cool thin gas
absorbs certain wavelengths
from a continuous spectrum,
leaving dark absorption lines
in their place superimposed
on the continuous spectrum.
Spectra and Background
Type of spectrum seen depends on the temperature of the
thin gas relative to the background temperature.
TOP: thin gas cooler than background, absorption lines seen.
BOTTOM: thin gas hotter than background, emission lines seen.
Studying the Stars:
Analyzing the light from a star can tell us:
1. The composition of the star.
2. The relative motion & rotation of the star.
3. The star’s temperature.
Shows limited Range of Light Energies Reaching Earth’s Surface