LAMDA level energies are approximate and cannot be used to derive line energies (trac #334)

[cloudy-bot]

reported by: @CloudyLex

We use level energies to derive line wavelengths in the LAMDA database. The level energies are frequently only given to ~5 significant figures. The levels are closely spaces to this carries over into a significant uncertainty in the line wavelength.

The fix is to use the line frequencies, also in the LAMDA file, to set the line energy/frequency/wavelength.

Note from Nick:

I think there is a discrepancy.  If I take transition #2, which is the difference in 
the energy of level 3 to level 1, I get 0.0556.  However, the third transition, 
which is the difference between level 4 and level 2, is also 0.0556.  This is why 
the same wavelength appears, because of the same energy difference.  You are 
correct, the energies need better precision for molecules with hyperfine 
structure.

I get a wavelength of 17.9860c for the two transitions.  I took the difference of 
0.0556, multiplied by the ERG1CM conversion factor in Cloudy, then used the 
same value of Planck's constant and the speed of light in Cloudy to get the 
wavelength.  

Migrated from https://www.nublado.org/ticket/334

{
    "status": "new",
    "changetime": "2019-02-04T13:19:03Z",
    "_ts": "1549286343684492",
    "description": "We use level energies to derive line wavelengths in the LAMDA database.  The level energies are frequently only given to ~5 significant figures.  The levels are closely spaces to this carries over into a significant uncertainty in the line wavelength.\n\nThe fix is to use the line frequencies, also in the LAMDA file, to set the line energy/frequency/wavelength.\n\nNote from Nick:\n\n{{{\nI think there is a discrepancy.  If I take transition #2, which is the difference in \nthe energy of level 3 to level 1, I get 0.0556.  However, the third transition, \nwhich is the difference between level 4 and level 2, is also 0.0556.  This is why \nthe same wavelength appears, because of the same energy difference.  You are \ncorrect, the energies need better precision for molecules with hyperfine \nstructure.\n\nI get a wavelength of 17.9860c for the two transitions.  I took the difference of \n0.0556, multiplied by the ERG1CM conversion factor in Cloudy, then used the \nsame value of Planck's constant and the speed of light in Cloudy to get the \nwavelength.  \n}}}",
    "reporter": "gary",
    "cc": "",
    "resolution": "",
    "time": "2015-07-06T21:35:21Z",
    "component": "atomic/molecular data base",
    "summary": "LAMDA level energies are approximate and cannot be used to derive line energies",
    "priority": "good to do",
    "keywords": "",
    "version": "trunk",
    "milestone": "no milestone",
    "owner": "nobody",
    "type": "defect - wrong answer"
}

[cloudy-bot]

• @CloudyLex commented:

Nick derived accurate level energies for the three lowest levels of OH. With r10537 OH now has correct line wavelengths and energies. Checks showed that OH was the only one of the LAMDA molecules which had low precision energies.

This issue is resolved for OH and LAMDA appears OK as we now have it. But it would be very nice to have the ability to use their line frequencies, which are quoted to high precision, rather than relying on their energies. So I am demoting this from a blocker to C16 to something good to do for the database.

• @CloudyLex changed milestone from "C16_branch" to "database infrastructure"
• @CloudyLex changed priority from "blocker" to "good to do"

[cloudy-bot]

@peter-van-hoof-noaccount changed milestone from "database infrastructure" to "no milestone"