Light, electromagnetic spectrum

This experiment is designed to support classroom discussions about light, the electromagnetic spectrum, light absorption, spectrophotometers, etc. It also brings to light a typical problem real-world industrial chemists face at times, and that is the analysis of an offcolor or out-of-spec material. This experiment could be combined with Experiment 8 in the same lab period. 

In the electromagnetic spectrum, the ultra violet region is between that of X-rays and visible light. This corresponds to the energies hv ot one hundred to a few tens of electron-volts (wavelengths from 180 to 400 nm). 

Spectroscopy, or the study of the interaction of light with matter, has become one of the major tools of the natural and physical sciences during this century. As the wavelength of the radiation is varied across the electromagnetic spectrum, characteristic properties of atoms, molecules, liquids and solids are probed. In the... 

The so-called peak power delivered by a pulsed laser is often far greater than that for a continuous one. Whereas many substances absorb radiation in the ultraviolet and infrared regions of the electromagnetic spectrum, relatively few substances are colored. Therefore, a laser that emits only visible light will not be as generally useful as one that emits in the ultraviolet or infrared ends of the spectrum. Further, witli a visible-band laser, colored substances absorb more or less energy depending on the color. Thus two identical polymer samples, one dyed red and one blue, would desorb and ionize with very different efficiencies. 

Neodymium and YAG Lasers. The principle of neodymium and YAG lasers is very similar to that of the ruby laser. Neodymium ions (Nd +) are used in place of Cr + and are often distributed in glass rather than in alumina. The light from the neodymium laser has a wavelength of 1060 nm (1.06 xm) it emits in the infrared region of the electromagnetic spectrum. Yttrium (Y) ions in alumina (A) compose a form of the naturally occurring garnet (G), hence the name, YAG laser. Like the ruby laser, the Nd and YAG lasers operate from three- and four-level excited-state processes. 

The scattering of visible light by polymer solutions is our primary interest in this chapter. However, since is a function of the ratio R/X, as we saw in the last section, the phenomena we discuss are applicable to the entire range of the electromagnetic spectrum. Accordingly, a general review of the properties of this radiation and its interactions with matter is worthwhile before a specific consideration of scattering. 

In 1957, this team of brothers-in-law started working together on Townes s idea for an optical maser. They found atoms that they felt had the most potential, based on transitional probabilities and lifetimes. However, there was still one major problem In the visible light portion of the electromagnetic spectrum, atoms don t remain in an excited state as long as... 

Absorption spectrum (Section 12.5) A plot of wavelength of incident light versus amount of light absorbed. Organic molecules show absorption spectra in both the infrared and the ultraviolet regions of the electromagnetic spectrum. 

C07-0007. A compact disc player uses light of frequency 3.85 X lO s to read the information on the disc, (a) What is this light s wavelength (b) In what portion of the electromagnetic spectrum (visible, ultraviolet, and so on) does this wavelength fall (c) What is the energy of one mole of photons at this frequency ... 

Each element has unique absorption and emission spectra. That is, each element has its own set of characteristic frequencies of light that it can absorb or emit. Also, Figures 7-10 and 7-11 show only the visible portions of absorption and emission spectra. Electron transitions also take place in regions of the electromagnetic spectrum that the human eye cannot detect. Instmments allow scientists to see into these regions. 

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