Infrared Spectroscopy - An Overview
Except for the very lightest elements (primarily hydrogen and helium),
which resulted from the Big Bang,
most of the atoms and molecules in the Universe have their origins
in the stars. As stars burn and eventually die out, they produce
heavier elements which are then ejected into interstellar space as a star
blows off its outer layers during its final phases.
Some of these elements will then combine to form molecules.
Atoms and molecules are the basic building blocks of all matter.
Determining which atoms and molecules are present in space, what their
distribution and abundance is, and in what environments they exist is
critical to our understanding of the Universe, the formation of stars,
planets and galaxies, and the possibility of life beyond the Earth.
The infrared part of the spectrum is where the emission and absorption lines
of virtually all molecules as well as
numerous atoms and ions (electrically charged atoms) lie.
Infrared spectroscopy is the primary way to detect these elements in space.
Spectrometers onboard infrared missions like the
Kuiper Airborne Observatory (KAO),
and the Infrared Space Observatory
(ISO), as well as near-infrared spectra from ground based observatories,
have led to the discovery of hundreds of atoms and molecules
in many different regions of space.
Infrared spectra of the molecule CH4 - one of at least ten
new molecules detected by ISO.
Credit: ESA/ISO, SWS, H. Feuchtgruber et al.
Since infrared can penetrate heavy dust, which often surrounds objects like
newly forming stars and our galactic center, infrared spectroscopy can
provide information about environments which are hidden from optical view,
such as regions of star formation and the center of our galaxy.
As a result of the Big Bang, the Universe is expanding. This causes
spectral lines which would normally appear in the ultraviolet and visible
part of the spectrum to be
doppler shifted into the infrared for very distant objects.
This means that infrared spectroscopy is a valuable tool for understanding
conditions in the early Universe. An example of this can be seen in the
spectrum of the most distant quasar currently known.
The doppler shift of spectral lines also allows astronomers to detect
and measure the velocity of planets around stars, stars around stars,
expanding stellar atmospheres, outflows from
star forming regions, rotating rings in galaxies, rotating spiral arms,
supernova explosions, and shock waves from colliding galaxies.
Infrared light is radiated from any object with a temperature.
Even objects which are too cool to be detected optically can be studied in the
For example, the
ISO spectra (left)
led to the discovery of a new molecule in interstellar space.
The molecule, CH4, is one of the most important tracers for
the formation of complex carbon-based molecules.
It was detected in very cold and thin molecular clouds by its
infrared absorption lines. The discovery of this molecule and
the measurement of its abundance will lead to a better estimate of the
abundance of hydrocarbons in space. To see some of the molecules which have
already been discovered in interstellar space
Infrared spectral studies are providing stunning information about the role of
interstellar molecules in the formation of stars, planets and possibly even
For example, infrared spectroscopy has shown that
water is abundant in many regions of space
and it is likely that the water we have here on Earth originated
from stars which died out long before our solar system was formed.
silicates, the most abundant mineral on Earth, is also found in abundance
in interstellar space.
Recent infrared spectral data have shown that complex
organic molecules can form rapidly (over a few thousand years) in
the environments around old stars and are abundant in many regions of space.
These elements and molecules will likely find their way
into new stars and planets as they form from molecular clouds.
These are just a few examples of discoveries resulting from
New infrared missions such
(The Stratospheric Observatory For Infrared Astronomy)
and the Spitzer Space Telescope
will include infrared spectrometers
which will lead to a greater understanding of the chemistry of the
Infrared Spectroscopy Index |
What is Spectroscopy? |
Infrared Spectroscopy |
Solar System |
Interstellar Space |
Star Forming Regions |
Older Stars |
Search For Life |
Our Galaxy |
Other Galaxies |