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Hello Franck, Margarida, and anybody interested in LineTAP,<br>
<br>
Regarding all the discussions that followed the Margarida's talk,
James and I think there is a clearly a room to continue them in the
next DAL Running Meeting. No date set currently, and no pressure
from us to do so. But if you are interested, just tell us and we can
start to organize that.<br>
<br>
Cheers,<br>
Grégory and James<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 28/04/2022 18:21, Franck Le Petit
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1B0DFE69-6DD1-4882-8D12-6B09586F8B26@obspm.fr">
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<div class="">Hello, </div>
<div class=""><br class="">
</div>
<div class="">Following Margarida nice presentation about LineTAP,
here are some comments and questions. </div>
<div class=""><br class="">
</div>
<div class=""><b class="">1 - Choice of units for energy levels</b></div>
<div class="">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. </div>
<div class=""><br class="">
</div>
<div class="">That is not an issue if users never see these
quantities in Joule, if, for instance, they are converted in
other units. </div>
<div class="">If users see these values in Joule then, that is a
bad choice and another unit should be chosen. </div>
<div class=""><br class="">
</div>
<div class="">The most important point here, for energy levels and
line wavelengths is the precision. </div>
<div class="">Spectroscopy is one of the domain of Physics where
the precision on data is very large. And, in astrophysics we
need this precision on spectroscopic data. </div>
<div class=""><br class="">
</div>
<div class="">So : </div>
<div class="">1 - The VO interfaces should not introduce a lost of
precision for example manipulating very small numbers (energy of
a hyperfine transitions in Joule) and very large numbers. </div>
<div class="">2 - A unit conversion system is mandatory but it is
difficult to write a reliable one. </div>
<div class="">Up to 2019, the Boltzman constant was not very
precise. So, any unit conversion done using the Boltzman
constant introduced a significant error. For instance,
spectroscopists determine rotational level energies in cm-1
because it is convenient and precise. When these energies were
converted in Kelvin, because of the imprecision on the Boltzmann
constant, these operation introduced significant errors on the
energy levels.</div>
<div class=""><br class="">
</div>
<div class="">In 2019, physical constants have been redefined and
this issue has been solved. The Boltzmann constant, as the
velocity of light, etc … are now exact. But this means that any
unit conversion system must use the latest values of the
physical constants and that, the numerical values of energy
levels or line wavelengths must not be truncated. The less we
have to convert units, the less errors will be introduced in the
system. </div>
<div class="">We should avoid the situation where each data
provider and each client has to implement unit conversion
system. We can be sure there will have mistakes. </div>
<div class=""><br class="">
</div>
<div class=""><b class="">2 - Zero point energy</b> </div>
<div class=""><br class="">
</div>
<div class="">You mentioned the zero point energy and I do not
understand the problem. </div>
<div class=""><br class="">
</div>
<div class="">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. </div>
<div class=""><br class="">
</div>
<div class="">But, this quantity is useful in chemistry not in
spectroscopy. So, why do we need it for LineTAP ? It is not an
issue if we say that the H2 v=0 J=0 level is at 0.00000 K and
the HD v=0 J=0 level is also at 0.00000 K even if these two
zeros are not the same. Indeed, for spectroscopy, we will never
do operations between energy levels of H2 and HD. So, each
molecule as its 0.000 level energy that is not the same between
molecules. But, for our problem of line indentification that is
not an issue. </div>
<div class=""><br class="">
</div>
<div class="">So in my opinion, LineTAP should not deal with zero
point level energy. </div>
<div class=""><br class="">
</div>
<div class=""><b class="">3 - Einstein coefficients, Oscillator
strengths and others</b></div>
<div class=""><br class="">
</div>
<div class="">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. </div>
<div class=""><br class="">
</div>
<div class="">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 : </div>
<div class="">Aki = 6.6702E15 / lambda**2 * g_i / g_k * f_ik</div>
<div class=""><br class="">
</div>
<div class="">So, we need the degeneracies of the levels and those
one depends on the physical effects that are considered (ex :
hyperfine structure or not).</div>
<div class="">To understand a numerical value for the
degeneracies, one need to know the quantum numbers. </div>
<div class=""><br class="">
</div>
<div class="">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 ? </div>
<div class=""><br class="">
</div>
<div class="">Best regards</div>
<div class="">Franck</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
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