Absorption Spectrum

[kenhung123]

How is an absorption spectrum obtained? Is it obtained from AAS? Because as far as I know, the AAS only uses specific wavelength so how does it produce an absorption spectrum (coloured background with dark lines). Colorimetry and UV visible has a graph of absorbance vs wavelength graph as its spectrum also.

[cameron_15]

The dark background with coloured lines is the emission spectrum, obtained from atomic emission spectroscopy (AES), not Atomic absorbtion (AAS).

AES Is like a flame test except it uses a hotter flame (to ensure enough energy is available for all the electrons that can move to another energy level, do) and the emitted light is passed through a slit, then a prism to seperate the light into different wavelengths.

If any of this is wrong, feel free to correct me. I need to learn this to!

Edit: Ok that was silly, Misread your post.

I to would like to know the answer to your question.

[kenhung123]

I think the emission spectrum is a black background with coloured lines..

[Stroodle]

Yeah. Absorption spectrum has black lines with coloured background.

Edit* I remember reading that an absorption spectrum occurs when light is passed through a dilute gas, since then the re-emmited light isn't likely to emitted in the same direction as the incident light, hence giving dark lines.

[cameron_15]

My mistake, read the coloured background, black lines part around the wrong way

[kenhung123]

Yeah. Absorption spectrum has black lines with coloured background.

Edit* I remember reading that an absorption spectrum occurs when light is passed through a dilute gas, since then the re-emmited light isn't likely to emitted in the same direction as the incident light, hence giving dark lines.

In AAS? As far as the textbook shows, it only uses selected wavelengths (cathode lamp) and detects the amount of the wavelengths being absorbed by a sample. That cannot show a spectrum.

[Stroodle]

Yeah. Absorption spectrum has black lines with coloured background.

Edit* I remember reading that an absorption spectrum occurs when light is passed through a dilute gas, since then the re-emmited light isn't likely to emitted in the same direction as the incident light, hence giving dark lines.

In AES? As far as the textbook shows, it only uses selected wavelengths (cathode lamp) and detects the amount of the wavelengths being absorbed by a sample. That cannot show a spectrum.

I think you meant AAS?

I don't think any of the instruments we study produce an absorption spectrum with dark lines.
In UV/Vis when you initially scan the sample to see which wavelength is absorbed the most, something similar would be produced, but the sample would re-emmit the absorbed light, and some of this would go to the sensor, so it wouldn't be a black line; just a lower intensity.
THis is just my speculation though...

[kenhung123]

Ah yes AAS, got confused!