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Discussion

Slide 1: The scale in the hand-held spectroscope

The spectrum is displayed below the scale that is to the right of the slit. The numbers on the scale mark hundreds of nanometers, and the thick dashed lines are 50 nanometer increments. Each thin solid line on the scale represents 10 nanometers.

Slide 2: Recording an emission spectrum with a blue line at about 445 nm, a green line at 525 nm, and a red line at 635 nm

The emission spectrum is a result of the excitation of an electron and its subsequent return to the ground state. Since elements have their own distinct allowable excitation levels, each element will have its own distinct emission spectrum.

Because of this uniqueness, an emission spectrum is like a fingerprint. Thus, it is important to accurately record the wavelength and appearance of each emission. The emission lines can be sketched or tabulated.

Regardless of how the data is organized, careful notes should be taken. Some lines will be very intense or very weak, other lines may appear as singlets, doublets, or multiplets. Since some spectra contain a large number of lines, it is often convenient to develop a set of abbreviations for the appearance of the emission lines. Some common abbreviations are listed below.

Common abbreviations:
s - singlet
d - doublet
t - triplet
h - high intensity line
m - medium intensity line
l - low intensity line

Slide 3: Recording an absorption spectrum with absorptions at 460 - 470 nm, 550 - 556 nm, 557 - 559 nm, and 605 - 610 nm

An absorption spectrum may be difficult to observe with a hand-held spectroscope. Look for regions of the continuous spectrum where the intensity of the light is weaker. The absorption regions may be completely black (no light at the observed frequencies is passing through the sample), but are more likely to be only slightly dimmer that the rest of the spectrum. Moving the sample in and out of the path between the light source and the slit will sometimes make the darker regions more obvious (since any change in the spectrum might be noticed).

Slide 4: Calibration of a hand-held spectroscope

Readings obtained from a hand-held spectroscope may not correlate precisely with known values measured with more sophisticated instruments. Therefore, calibrating the spectroscope is necessary.

First, obtain a set of known emission wavelengths for a gas that is available from a reference source. Then, record the wavelengths observed for the gas using the spectroscope. Prepare a graph of known (reference) wavelengths versus observed wavelengths. From this calibration plot, observed emission lines can be corrected to agree with wavelengths recorded with more accurate instrumentation.