J/ApJ/716/1315 Hyperfine levels of N2H+ (Keto+, 2010)
Modeling molecular hyperfine line emission.
Keto E., Rybicki G.
<Astrophys. J., 716, 1315-1322 (2010)>
=2010ApJ...716.1315K 2010ApJ...716.1315K
ADC_Keywords: Atomic physics
Keywords: ISM: molecules - radiative transfer
Abstract:
In this paper, we discuss two approximate methods previously suggested
for modeling hyperfine spectral line emission for molecules whose
collisional transition rates between hyperfine levels are unknown.
Hyperfine structure is seen in the rotational spectra of many commonly
observed molecules such as HCN, HNC, NH3, N2H+, and C17O. The
intensities of these spectral lines can be modeled by numerical
techniques such as Λ-iteration that alternately solve the
equations of statistical equilibrium and the equation of radiative
transfer. However, these calculations require knowledge of both the
radiative and collisional rates for all transitions. For most commonly
observed radio frequency spectral lines, only the net collisional
rates between rotational levels are known. For such cases, two
approximate methods have been suggested. The first method, hyperfine
statistical equilibrium, distributes the hyperfine level populations
according to their statistical weight, but allows the population of
the rotational states to depart from local thermal equilibrium (LTE).
The second method, the proportional method, approximates the collision
rates between the hyperfine levels as fractions of the net rotational
rates apportioned according to the statistical degeneracy of the final
hyperfine levels. The second method is able to model non-LTE hyperfine
emission. We compare simulations of N2H+ hyperfine lines made with
approximate and more exact rates and find that satisfactory results
are obtained.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 22 64 N2H+ hyperfine levels
table3.dat 45 280 N2H+ hyperfine level data
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See also:
J/A+A/413/1177 : Spectroscopy of N2D+ hyperfine structure (Dore+, 2004)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Level [1/64] Level index
5- 11 F7.4 cm-1 E Energy of level
13- 16 F4.1 --- g Statistical weight
18 I1 --- J [0/7] J rotational quantum number
20 I1 --- F1 [0/8] F1 hyperfine quantum number
22 I1 --- F [0/9] F hyperfine quantum number
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Trans [1/280] Transition index
5- 6 I2 --- Up [4/64] Upper state (index from table2)
8- 9 I2 --- Low [1/55] Lower state (index from table2)
11- 20 E10.4 s-1 A Einstein A coefficient
22- 32 F11.7 GHz Freq [93.1716/652.099] Frequency
34- 45 A12 --- RInt Relative intensity
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 01-Jun-2012