2018A&A...616A.166C


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST15:32:58

2018A&A...616A.166C - Astronomy and Astrophysics, volume 616A, 166-166 (2018/8-1)

Photoinduced polycyclic aromatic hydrocarbon dehydrogenation The competition between H- and H2-loss.

CASTELLANOS P., CANDIAN A., ZHEN J., LINNARTZ H. and TIELENS A.G.G.M.

Abstract (from CDS):

Polycyclic aromatic hydrocarbons (PAHs) constitute a major component of the interstellar medium carbon budget, locking up to 10-20% of the elemental carbon. Sequential fragmentation induced by energetic photons leads to the formation of new species, including fullerenes. However, the exact chemical routes involved in this process remain largely unexplored. In this work, we focus on the first photofragmentation steps, which involve the dehydrogenation of these molecules. For this, we consider a multidisciplinary approach, taking into account the results from experiments, density functional theory (DFT) calculations, and modeling using dedicated Monte-Carlo simulations. By considering the simplest isomerization pathways - i.e., hydrogen roaming along the edges of the molecule - we are able to characterize the most likely photodissociation pathways for the molecules studied here. These comprise nine PAHs with clearly different structural properties. The formation of aliphatic-like side groups is found to be critical in the first fragmentation step and, furthermore, sets the balance of the competition between H- and H2-loss. We show that the presence of trio hydrogens, especially in combination with bay regions in small PAHs plays an important part in the experimentally established variations in the odd-to-even H-atom loss ratios. In addition, we find that, as PAH size increases, H2 formation becomes dominant, and sequential hydrogen loss only plays a marginal role. We also find disagreements between experiments and calculations for large, solo containing PAHs, which need to be accounted for. In order to match theoretical and experimental results, we have modified the energy barriers and restricted the H-hopping to tertiary atoms. The formation of H2 in large PAHs upon irradiation appears to be the dominant fragmentation channel, suggesting an efficient formation path for molecular hydrogen in photodissociation regions (PDRs).

Abstract Copyright: © ESO 2018

Journal keyword(s): astrochemistry - ISM: molecules - methods: laboratory: molecular - molecular processes

Simbad objects: 1

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Number of rows : 1

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 7023 RNe 21 01 36.9 +68 09 48           ~ 630 0

    Equat.    Gal    SGal    Ecl

C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST15:32:58

Available data : Basic data  •  Identifiers  •  Plot & images  •  Bibliography  •  Measurements  •  External archives  •  Notes  •  Annotations


Basic data :
NGC 7023 -- Reflection Nebula
Origin of the objects types :

(Ref) Object type as listed in the reference "Ref"
(acronym) Object type linked to the acronym according to the original reference
() Anterior to 2007, before we can link the objet type to a reference, or given by the CDS team in some particular cases

Other object types:
Cl* (C,Cl,...), IR (IRAS,PSCz,...), OpC (OCISM,OCl), RNe ([RK68]), HII (LBN), ISM (GN), V* (AAVSO), UV ([SPB96])
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
ICRS coord. (ep=J2000) :
21 01 36.9 +68 09 48 [ ] D ~
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
FK4 coord. (ep=B1950 eq=1950) :
21 00 59.7 +67 57 55 [ ]
Syntax of coordinates is : "ra dec (wtype) [error ellipse] quality bibcode" :
  • ra dec : right ascension and declination (unit and frame defined according to your Output Options)
    Grey values are increasing the original precision due to the computation of frame transformations
  • (wtype) : wavelength class for the origin of the coordinates (Rad, mm, IR, Optical, UV, Xray, Gam)
  • [error ellipse] : measurement uncertainty, on (ra,dec) if the positional angle is 90 degrees, on (majaxis,minaxis) otherwise (in mas at defined epoch in the original catalogue),
    position angle (in degrees North celestial pole to East)
  • quality : flag of quality
    • E ≥ 10"
    • D : 1-10" (and some old data)
    • C : 0.1-1"
    • B : 0.01-0.1" + 2MASS, Tyc
    • A : VLBI, Hipparcos
  • bibcode : bibcode of the coordinates reference
Gal coord. (ep=J2000) :
104.0616 +14.1926 [ ]
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Identifiers (20) :
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NGC 7023 IRAS F21009+6758 NAME IRIS Nebula RAFGL 2695
C 2059+679 IRAS 20599+6755 OCISM 50 [BDB2003] G104.06+14.19
Cl VDB 139 IRAS F20599+6755 OCl 235 [RK68] 105
GN 21.01.0 LBN 104.08+14.21 PSCz P21009+6758 [SPB96] 2161
IRAS 21009+6758 LBN 487 PSCz P20599+6755 AAVSO 2044+67

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References (630 between 1850 and 2020) (Total 630)
Simbad bibliographic survey began in 1850 for stars (at least bright stars) and in 1983 for all other objects (outside the solar system).
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Observing logs


ISO : 236    herschel : 52   

   


External archives :

Archive data at HEASARC - High-Energy Astrophysics Science Archive Research Center

Data at NED - NASA/IPAC Extragalactic Database : NGC 7023

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NGC 7023 IRAS 21009+6758 IRAS F21009+6758 IRAS 20599+6755 IRAS F20599+6755
RAFGL 2695

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2020.07.04-15:32:58

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