LineTAP

[Pinheiro de Castro Neves, Margarida]

Hi Franck,


thanks for your input.

> On 28. Apr 2022, at 18:21, Franck Le Petit <Franck.LePetit at obspm.fr> wrote:
> 
> Hello, 
> 
> Following Margarida nice presentation about LineTAP, here are some comments and questions. 
> 
> 1 - Choice of units for energy levels
> I saw that Joule was proposed. Joule is a bit a strange unit for energy levels because 1 Joule is lot of energy whereas rotational levels or hyperfine structures contains very few energy. Using Joule means that we will have to manipulate quantities as 10E-XX where XX is a lot. 

Well, Joule was proposed as an unit, but at the end we decided to use Angstrom. Because, VAMDC uses it, and most of the spectra I find in the VO are in Angstrom, and then there’s no need to convert. But this can change when we get new data into the VO.
But I’ve learned yesterday that  Angstrom has been deprecated by the IAU. I think we need to discuss it again.
> 
> 2 - Zero point energy 
> 
> You mentioned the zero point energy and I do not understand the problem. 
> 
> The Zero point energy is a theoretical concept that represents the difference of energy between the bottom of the potential well of a molecule and the first level that can be populated. It is very complex to estimate precisely (and I guess it is a hot topic among specialists) because one has to consider many subtle quantum effect leading to correction terms on the zero order value 1/2 hbar omega. 

This issue was raised by Markus Demleitner, when implementing a LineTAP service. 
Perhaps this is not so problematic after all.
> 
> 3 - Einstein coefficients, Oscillator strengths and others
> 

> In the presentation, it was said that one can go from one of these quantities to the other ones by simple conversions. That is true but for some molecules that can be quite tricky and create debates between specialists. 
> 
> Moreover, to go from one quantity to another one, one often need another quantity that is the degeneracy of the levels. For example, to convert an oscillator strength in Einstein coefficients : 
> Aki = 6.6702E15 / lambda**2 * g_i / g_k * f_ik
> 
> So, we need the degeneracies of the levels and those one depends on the physical effects that are considered (ex : hyperfine structure or not).
> To understand a numerical value for the degeneracies, one need to know the quantum numbers. 
> 
> So, how does LineTAP deal with that or, more precisely, how will it provide enough information to users so that they can use properly the data ? 

I’m not an spectroscopist,  and here we need input from specialists.
The simple use case  is to provide a measurement that shows how strong a line is, how probable is this transition. 
I know that there are preferred quantities for different cases, like absorption/emission - But are this quantities equivalent?
Some databases provide only one of them, others provide another one, others more than one quantity.
Would only Aki do ?
For simplicity, we don’t want to provide all weights, quantum numbers, etc. They are described in the VAMDC and SSLDM data models but not all 
VAMDC databases provide them. 

Best regards,

Margarida

—

Margarida Castro Neves

German Astrophysical Virtual Observatory (GAVO)
Astronomisches Rechen-Institut (ARI)
Zentrum für Astronomie, Universität Heidelberg  (ZAH)
Mönchhofstr. 12 - 14, 69120 Heidelberg
phone +49-6221-54-1891   fax +49-6221-54-1888
mcneves at ari.uni-heidelberg.de
http://www.ari.uni-heidelberg.de