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Molecules in photospheres of carbon stars - C2, CN and SiC2 in W Orionis

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#1 mwr

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Posted 13 February 2021 - 11:41 AM

The spectrum of the cool carbon star W Orionis is dominated by a multitude of molecular bands (rectified spectrum recorded with a SA-200 grism):

 

Folie1.JPG

 

I have tried to assign these bands to their corresponding transitions. The vibronic structure of the Swan bands of the C2 radical can be nicely resolved and even the multiplet structures of the rovibronic levels of the CN radical are resolved in the near infrared:

 

Folie2.JPG

 

The SiC2 Merrill-Sanford absorption bands were well detectable between the Swan bands:

 

Folie3.JPG

 

The SiC2 has three normal modes of vibration (v1, v2, v3) and the strongest transition can be assigned to the (0,0,0) < (0,0,0) transition between the electronic ground state and the first excited electronic level (taken from : https://academic.oup...9/1/103/1074946 )

 

Folie4.JPG

 

While the notation of the combined vibrational modes is clear to me, the notation of the vibronic transitions in the upper scheme remained unclear to me  (e.g. 302)  (see red box). In my basic spectroscopy textbooks I couldn't find any explanation. Can somebody help me here in understanding this notation? Thanks in advance.


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#2 B McCandless

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Posted 13 February 2021 - 12:19 PM

From what I recall, the notation is not universal but refers to a transition N, having different lower and upper vibrational quantum numbers.


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#3 Tangerman

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Posted 13 February 2021 - 12:53 PM

After the last thread where I so enjoyed your spectra, I have to reply again. I'll quote from Modern Spectroscopy (Hollas), section 6.2.3.1 in case you wish to find it (and to give credit). "the transitions may be labeled 110, 210, and 310 according to a useful, but not universal, convention for polyatomic molecules in which Nv'v'' refers to a transition with lower and upper state vibrational quantum numbers v'' and v', respectively, in vibration N."


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#4 mwr

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Posted 13 February 2021 - 02:22 PM

From what I recall, the notation is not universal but refers to a transition N, having different lower and upper vibrational quantum numbers.

 

After the last thread where I so enjoyed your spectra, I have to reply again. I'll quote from Modern Spectroscopy (Hollas), section 6.2.3.1 in case you wish to find it (and to give credit). "the transitions may be labeled 110, 210, and 310 according to a useful, but not universal, convention for polyatomic molecules in which Nv'v'' refers to a transition with lower and upper state vibrational quantum numbers v'' and v', respectively, in vibration N."

Ah, the penny has dropped! Thank you both! 



#5 mwr

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Posted 15 February 2021 - 01:49 PM

After the last thread where I so enjoyed your spectra, I have to reply again. I'll quote from Modern Spectroscopy (Hollas), section 6.2.3.1 in case you wish to find it (and to give credit). "the transitions may be labeled 110, 210, and 310 according to a useful, but not universal, convention for polyatomic molecules in which Nv'v'' refers to a transition with lower and upper state vibrational quantum numbers v'' and v', respectively, in vibration N."

I have used this useful notation to label additionally some more of the weaker Merrill-Sanford bands (so called vibrational hot-bands) to bring this to an end:

 

W_Ori_Merrill_Sanford.jpg

 

The SiC2 molecule with three atoms is so far the "largest" molecule that I could detect with my low resolution setup in atmospheres of cool stars. Are there even larger molecules in stellar atmospheres that are detectable between 4000 and 9000 Angström ? (methane in planetary atmospheres is well detectable using the Star Analyser).


Edited by mwr, 15 February 2021 - 02:03 PM.


#6 Peter Z

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Posted 15 February 2021 - 02:55 PM

Beautiful job on the spectral measurements and analysis!

I am amazed what you can do with the SA-200.

Cheers.

Peter



#7 mwr

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Posted 15 February 2021 - 04:31 PM

Beautiful job on the spectral measurements and analysis!

I am amazed what you can do with the SA-200.

Cheers.

Peter

Thanks Peter!

So far, I had a lot of fun with the SA-200.




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