J/A+A/627/A65 HNCO, CH3CN and HCOOCH3 partition functions (Carvajal+, 2019)
Impact of non-convergence and various approximations of the partition function
on the molecular column densities in the interstellar medium.
Carvajal M., Favre C., Kleiner I., Ceccarelli C., Bergin E.A., Fedele D.
<Astron. Astrophys. 627, A65 (2019)>
=2019A&A...627A..65C 2019A&A...627A..65C (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: techniques: spectroscopic - ISM: abundances - radio lines: ISM
Abstract:
We emphasize that the completeness of the partition function, i.e. the
use of a converged partition function at the typical temperature range
of the survey, is very important to decrease the uncertainty on this
quantity and thus to derive reliable interstellar molecular densities.
In that context, we will show how the use of different approximations
for the rovibrational partition function together with some
interpolation and/or extrapolation procedures may affect the estimate
of the interstellar molecular column density. For that purpose, we
will apply the partition function calculations to astronomical
observations performed with the IRAM-30m telescope towards the
NGC7538-IRS1 source of the two following N-bearing molecules:
isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide
(CH3CN, a symmetric top molecule). The case of methyl formate
(HCOOCH3), which is an asymmetric top O-bearing molecule which
contains an internal rotor will also be discussed. Our analysis shows
that the use of different partition function approximations leads to
relative differences in the resulting column densities in the range of
9% up to 43%. Thus, we expect that this work turns out to be relevant
for surveys of sources with temperatures higher than 300 K and to
observations in the infrared.
Description:
The internal partition functions are computed for isocyanic acid
(HNCO), methyl cyanide (CH3CN) and methyl formate (HCOOCH3) up to
T=500K using a 1K interval. The rotational, vibrational, and torsional
(if appropriate) contributions are also provided.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 54 510 Rotational, vibrational and rovibrational partition
functions computed in the present work for
isocyanic acid (HNCO) and up to T=500K
using a 1K interval
tabled2.dat 54 510 Rotational, vibrational and rovibrational partition
function computed in the present work for methyl
cyanide (CH3CN) up to T=500K using a 1K interval
(from erratum, 2024, A&A, 685, C1,
updated on 06 Feb 2024)
tabled3.dat 71 510 *Rotational, torsional, vibrational and
rotational-torsional-vibrational partition function
computed in the present work for methyl formate
(HCOOCH3) up to T=500K using a 1K interval.
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Note on tabled3.dat: From temperatures higher than 330K, the classical
approximation for the rotational partition function is considered instead of
the direct sum (see text).
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Byte-by-byte Description of file: tabled1.dat tabled2.dat
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Bytes Format Units Label Explanations
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3- 9 F7.3 K T Temperature
13- 24 F12.6 --- Qrot Rotational partition function
32- 39 F8.6 --- Qvib Vibrational partition function
43- 54 F12.6 --- Qrv Rotational-vibrational partition function
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Byte-by-byte Description of file: tabled3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 9 F7.3 K T Temperature
13- 24 F12.6 --- Qrot Rotational partition function
32- 39 F8.6 --- Qtor Torsional partition function
47- 54 F8.6 --- Qvib Vibrational partition function
58- 71 F14.6 --- Qrvt Rotational-torsional-vibrational
partition function
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Acknowledgements:
Miguel Carvajal Zaera, miguel.carvajal(at)dfa.uhu.es
History:
01-Jul-2019: on-line version
06-Apr-2024: updated tabled2.dat from erratum
(End) M. Carvajal [U. Huelva, Spain], Patricia Vannier [CDS] 31-May-2019