Spectroscopy and Atomic Spectra A satellite orbiting the Earth contain gravitational potential energy. The satellite can orbit the Earth at any height. Or, it can contain any amount of gravitation energy—Its gravitational potential energy is continuous. Similar to the satellite, an electron orbiting the nucleus of an atom possesses electric potential energy. However, unlike satellites in orbits, t he electrons can only stay in a finite number of discrete energy levels (or orbits).  The energy levels of the atoms are ‘quantized’.

There are only certain allowed Atomic energy levels Gravitational potential energy level can be anywhere along the line… E Selection Rules: There are rules about if a transition from level i to level j can occur or not! i j Different elements have different energy level structure… Element A Element B

How does light tell us what things are made off? Every chemical element has its own unit spectral fingerprint. We can study the chemical composition of an astronomical object by observing its absorption or emission spectrum. Emission spectrum of Hydrogen Absorption spectrum of Hydrogen With a thermal spectrum background.

Astronomical Spectra We can learn a lot about a astronomical object by studying the spectra of the object…. There are three basic types of spectra: a. Thermal radiation Spectra: All objects with a finite temperature emit thermal radiation. b. Absorption Line Spectra: c. Emission Line Spectra: Click on image to start animation

Elemental Spectrums

Breath Testers Breath testers that operate on the principle of infrared light absorption are becoming increasingly popular within the law enforcement community.

Infrared Spectroscopy

Spectrohotometry Just as a substance can absorb visible light to produce color, many of the invisible radiations of the electromagnetic spectrum are likewise absorbed. Spectrophotometry, an important analytical tool, measures the quantity of radiation that a particular material absorbs as a function of wavelength and frequency. The quantity of light absorbed at any frequency is directly proportional to the concentration of the absorbing species. This is known as Beer’s Law.

UVand IR Spectrophotometry Currently, most forensic laboratories use UV and IR spectrophotometers to characterize chemical compounds. The simplicity of the UV spectrum facilitates its use as a tool for determining a material’s probable identity, although it may not provide a definitive result. The IR spectrum provides a far more complex pattern.

UVand IR Spectrophotometry Different materials always have distinctively different infrared spectra; each IR spectrum is therefore equivalent to a “fingerprint” of that substance.

The Spectrophotometer The spectrophotometer is the instrument used to measure and record the absorption spectrum of a chemical substance. The components of a spectrophotometer are: –A radiation source –A monochromator or frequency selector –A sample holder –A detector to convert electromagnetic radiation into an electrical signal –A recorder to produce a record of the signal Absorption spectra can be done in the visible, ultraviolet (UV) or infrared (IR) regions.