What is spectroscopy?

It is the study of how matter interacts with electromagnetic radiation

(gamma rays down to radio waves)Matter can interact with microwaves, radiowaves

Microwaves tuned to absorption frequency of water that is why the food gets hot.

What do you need to study spectroscopy?

Four fundamental components necessary to do spectroscopy Radiation source Sample Detector Dispersive element

UV Vis spectroscopy

Main focus is UV Vis spectroscopy Near IR into ultraviolet Other forms far IR or microwave or Xray all will

have similar elements... detectors will vary UV Vis- principle type of spectroscopy IR is very similar- UV and IR most used

UV Vis (and near IR-NIR)

250nm ---> 1000nm

3 ways to do spec

Absorption Excitation Emission

Radiation Sources Commonly used sources

Lasers– excitation source in spectroscopy

ideal excitation source for certain experiments (next week lecture on lasers) Not only great source but principles of operations intertwined with

spec.... Lasers designed based on spectroscopic principles

Atomic lamps

Mercury-Hydrogen,etc (fluorescent bulbs are mercury)

Broad spectrum UV

High pressure xenon lamp- xenon arc lamp Use quartz b/c transparent to UV- xenon gas- in and very bright-

very broad spectrum- useful for a wide variety of experiment

Tungsten lamp- like light bulb- visible light (not as expensive)

Halogen lamps

LEDs- Light emitting diodes

Experiment

How can we select only 500nm from a broad spectrum lamp?

Light is coming out of the bulb Filter the light

Sharp cut filter- everything below 510nm Still leaves 250 to 510nm Second filter out UV

Simpler way is dispersive devices-

Dispersive devices

Filters Prism- Optical device- put in light and then

comes out with range of colors

Light in-------> Refractive

Diffraction Grating--- Reflective – come off wavelength is angle

dependent- used in monochrometer

Sample----> Detectors What can be a detector? Eyeball- light detection Photodiode- electronic device- photon in --

>current Photomultiplier tube- Multiple photo diodes Single photon in- strike- release electrons--->

hit another grid---> releases more- cascading effect- one photon release millions of electrons

Extremely sensitive CCD- charged coupled device- in cameras (Diffraction grating coupled to detector Mirrors---monochromater)