Spectra of Planetary Atmospheres

[paulsutton]

Hi

I am not sure if this question is quite in the right place,  but it seems appropriate.

Just been watching the August Space telescope science institute lecture, looking at images and spectra from the James Webb Telescope,

https://www.stsci.edu/contents/events/pls/2022/webbs-first-look-images-and-spectra-from-nasas-newest-great-observatory

I have a question regarding a slide on atmosphere spectra to determine the composition and have attached a screenshot of the slide

According to this,  Some of the molecules exist at different ranges in the electromagnetic spectrum for example Water seems to be at between 5000 and 10,000 nm but also between (or closer to) 20,000nm

Is this due to how these molecules exist in the atmosphere so Liquid and gaseous states,   I think they said they detected water haze on the planet described.

Or is there another reason why molecules appear in more than one place.?

I am not too sure on the right terminology but do understand that different molecules are absorbed and hence we can work out by absorption which molecules they are.

 

Thanks

 

Paul Sutton

[exchemist]

2 hours ago, paulsutton said:

Hi

I am not sure if this question is quite in the right place,  but it seems appropriate.

Just been watching the August Space telescope science institute lecture, looking at images and spectra from the James Webb Telescope,

https://www.stsci.edu/contents/events/pls/2022/webbs-first-look-images-and-spectra-from-nasas-newest-great-observatory

I have a question regarding a slide on atmosphere spectra to determine the composition and have attached a screenshot of the slide

According to this,  Some of the molecules exist at different ranges in the electromagnetic spectrum for example Water seems to be at between 5000 and 10,000 nm but also between (or closer to) 20,000nm

Is this due to how these molecules exist in the atmosphere so Liquid and gaseous states,   I think they said they detected water haze on the planet described.

Or is there another reason why molecules appear in more than one place.?

I am not too sure on the right terminology but do understand that different molecules are absorbed and hence we can work out by absorption which molecules they are.

 

Thanks

 

Paul Sutton

IR radiation is of the right order of frequency to set up vibration in molecules which have a dipole (partial charge separation), giving up its energy to the molecule in the process. So this is what makes a molecule absorb in the IR.

What you are seeing is absorption due to different modes of vibration of the molecule. CO2 can stretch or it can bend. I rather think the left hand band is the stretch and the right hand one is the bend. 

So it's not several different species. It's all CO2. In general, the IR spectrum of a given molecule has a number of absorption regions, not just one. 

 

 

Edited August 5, 2022 by exchemist

[paulsutton]

22 hours ago, exchemist said:

IR radiation is of the right order of frequency to set up vibration in molecules which have a dipole (partial charge separation), giving up its energy to the molecule in the process. So this is what makes a molecule absorb in the IR.

What you are seeing is absorption due to different modes of vibration of the molecule. CO2 can stretch or it can bend. I rather think the left hand band is the stretch and the right hand one is the bend. 

So it's not several different species. It's all CO2. In general, the IR spectrum of a given molecule has a number of absorption regions, not just one.

Thank you for this,  it makes more sense now,.  So I guess the same would apply to  other molecules being in different places, that have the right properties for vibrations.   I think water does as I read about that years ago.

Interesting stuff. The JWST is going to hopefully gives us lots of science, so will be good to see what papers & articles etc are published over the coming years.

Paul

Edited August 6, 2022 by paulsutton

[exchemist]

1 hour ago, paulsutton said:

Thank you for this,  it makes more sense now,.  So I guess the same would apply to  other molecules being in different places, that have the right properties for vibrations.   I think water does as I read about that years ago.

Interesting stuff. The JWST is going to hopefully gives us lots of science, so will be good to see what papers & articles etc are published over the coming years.

Paul

Yes exactly. The spectrum of any element or compound is usually a series of lines (atoms) or bands (molecules) of absorption or emission at characteristic wavelengths, corresponding to the various natural excitations that are possible in the species in question.

With a complex mixture it can be quite tricky disentangling them and assigning them to whatever is responsible. One generally looks first for certain strong lines or bands that are not often overlain by something else, or in the case of water certain features like the broad blob of absorption it gives in the IR. Once you know it is there, you can allow for what it may be doing elsewhere, to obscure other things that may also be present, hidden behind it.