Doppler vs pressure broadening? (1 Viewer)

[Run hard@thehsc]

^^^^ wut the difference between these two when it comes to spectra? Thanks!!!

 

[tyrone97]

Doppler broadening is driven by the fact that the source of light is moving towards (blue shifting) or away (red shifting) from the observer. This can be due to random thermal motion or in the context of stellar spectra, the rotation of the source (i.e. if the star is rotating, one half rotates towards the observer, while the other half is rotating away).

Pressure broadening is driven by the fact that atoms colliding with each other cause changes in the energy levels of the electron.

 

[Run hard@thehsc]

fair - how can we differentiate these two when given a spectra, since both of these result in the thickness of the line spectra increasing? Thanks!

 

[tyrone97]

I don't think this it is a meaningful question to ask how the two can be differentiated because in practice, when you look at absorption or emission spectrum it will be broadened due to multiple factors at the same time (i.e. the pressure broadening is layered on top of doppler broadening). You would need to now more about the circumstances in which the spectra were produced to deduce which is more dominant (e.g. high temp low pressure -> doppler broadening, low temp high pressure -> pressure broadening).

 

[Run hard@thehsc]

I don't think this it is a meaningful question to ask how the two can be differentiated because in practice, when you look at absorption or emission spectrum it will be broadened due to multiple factors at the same time (i.e. the pressure broadening is layered on top of doppler broadening). You would need to now more about the circumstances in which the spectra were produced to deduce which is more dominant (e.g. high temp low pressure -> doppler broadening, low temp high pressure -> pressure broadening).

fair enof that makes sense - suppose we were asked to explain a broadened line spectra, is it still viable if we list both of these as reasons?