Line spectrum and Band spectrum

[logearav]

Revered members,

What is the difference between line spectrum and band spectrum? I have seen the line spectrum exhibited by Mercury vapour lamp and Hydrogen vapour lamp. My teacher says that band spectrum is similar to line spectrum and said that band spectrum is nothing but a line spectrum with large width. Is that true?

[swansont]

Revered members,

What is the difference between line spectrum and band spectrum? I have seen the line spectrum exhibited by Mercury vapour lamp and Hydrogen vapour lamp. My teacher says that band spectrum is similar to line spectrum and said that band spectrum is nothing but a line spectrum with large width. Is that true?

 

In my experience band spectra refer to condensed-matter-type systems where you have many atoms and line spectra are not present owing to the Pauli exclusion principle. So yes, the statement that band spectra are wider would be true, but one should also understand why that is the case.

[logearav]

Thanks swansont. But Mercury vapour which means mercury gas is also an example of many atoms system, isn't it?

[John Cuthber]

Iodine vapour has a band spectrum it's purple (other colours happen too, but the purple colour of iodine is quite well known)

If you look in detail at the spectrum you will see that it's made up of lots of lines very close together in the green region of light.

If you don't look so closely it's just a splodgy looking broad absorption.

There's a picture of it here

http://home.sou.edu/~chapman/ch445/Iodine.htm

 

The different absorbtions occur because, in addition to moving the electron from one excited state to another, the molecule is left vibrating. The different amounts of vibration correspond to different energies and so to different wavelengths of light.