J/A+A/681/L19 HCNH+ abundance in cold dense clouds (Bop+, 2024)
HCNH+ abundance in cold dense clouds based on the first hyperfine resolved rate
coefficients.
Bop T.C., Agundez M., Cernicharo J., Lefloch B., Lique F.
<Astron. Astrophys. 681, L19 (2024)>
=2024A&A...681L..19B 2024A&A...681L..19B (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: molecular data - molecular processes - radiative transfer -
scattering - ISM : abundances - ISM: molecules
Abstract:
The protonated form of hydrogen cyanide, HCNH+, holds significant
importance in astrochemistry, serving as an intermediate species in
ion-neutral reactions occurring in the cold molecular clouds. Although
it plays a crucial role in the chemistry of HCN and HNC, the
excitation rate coefficients of this molecular cation by the dominant
interstellar colliders have not been thoroughly investigated, leading
to limitations in radiative transfer models use to derive its
abundance. We present here the first hyperfine-resolved excitation
rate coefficients for HCNH+ induced by collisions with both He and
H2 at low temperatures, addressing a crucial requirement for precise
modeling of HCNH+ abundance in typical cold dense molecular clouds.
Using non-local thermodynamic equilibrium (LTE) radiative transfer
calculations, we reproduce fairly well the 1-->0 and 2-->1
observational spectra of HCNH+ and derive updated molecular column
densities. For the TMC-1 molecular cloud, the new HCNH+ abundance is
twice larger than suggested by previous LTE modeling, whereas the
column density of this molecular cation is improved only by 10% in
the case of the L483 proto-star. The factor of 2 in the case of TMC-1
most likely arises from an error in the early analysis of
observational spectra rather than an effect of the LTE assumption,
given that the HCNH+ lines are predominantly thermalized at
densities higher than 2x104cm-3. For multiline studies of clouds
of moderate density, we strongly recommend to use the collisional rate
coefficients reported in this work.
Description:
The first hyperfine resolved rate coefficients of HCNH+ induced by
collision with H2 and He was derived using the most accurate
recoupling method based on nuclear spin-independent scattering
matrices calculated by mean of the close-coupling quantum mechanical
approach. The data are in cm-3.s-1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
hcnhp-el.dat 34 25 Rotational energy levels of HCNH+
hcnhp-h2.dat 120 324 HFS rates due to collision with H2
hcnhp-he.dat 120 324 HFS rates due to collision with He
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Byte-by-byte Description of file: hcnhp-el.dat
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Bytes Format Units Label Explanations
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4- 5 I2 --- Level [1/25] Level identification number
10- 19 F10.7 --- E Energy
24- 27 F4.1 --- Weith Weight
32- 34 A3 --- J-F J and F transition (J_F)
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Byte-by-byte Description of file: hcnhp-h2.dat hcnhp-he.dat
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Bytes Format Units Label Explanations
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6- 8 I3 --- Trans Trasnsition identification number
15- 16 I2 --- Up [1/25] Upper level number
23- 24 I2 --- Low [1/25] Lower level number
29- 40 E12.7 cm-3.s-1 RCT5 First hyperfine resolved rate coefficient
for T=5.0K
45- 56 E12.7 cm-3.s-1 RCT10 First hyperfine resolved rate coefficient
for T=10.0K
61- 72 E12.7 cm-3.s-1 RCT15 First hyperfine resolved rate coefficient
for T=15.0K
77- 88 E12.7 cm-3.s-1 RCT20 First hyperfine resolved rate coefficient
for T=20.0K
93-104 E12.7 cm-3.s-1 RCT25 First hyperfine resolved rate coefficient
for T=25.0K
109-120 E12.7 cm-3.s-1 RCT30 First hyperfine resolved rate coefficient
for T=30.0K
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Acknowledgements:
Tidiane Cheikh Bop, cheikhtidiane.bop(at)ucad.edu.sn
(End) Patricia Vannier [CDS] 06-Jan-2024