Query : 2017A&A...607A..61Z

2017A&A...607A..61Z - Astronomy and Astrophysics, volume 607A, 61-61 (2017/11-1)

Search for hydrogen-helium molecular species in space.


Abstract (from CDS):

Context. Helium, the second most abundant element in the Universe, with a relative abundance of He/H∼1/10, has never been observed in any other form than that of a neutral atom (He) or an ion (He+) in the interstellar medium. Since He is a noble gas its non-observation as part of neutral molecular systems is understandable, but it is very surprising for a positively charged species such as HeH+ that is a stable diatomic ion whose spectral signatures are well known in the laboratory.
Aims. This non-observation, even in hydrogen rich regions, could imply that HeH+ is not a proper target and that alternatives have to be considered, such as small HeHn+ clusters. The present study aims at finding whether the leading term HeH3+ fulfills the conditions required.
Methods. We addressed the question with state-of-the-art numerical simulations. We determined a two-dimension ab initio potential energy surface (PES) of the HeH3+ cluster along the He...H3+ and HeH+...H2 reaction coordinates. The calculations rely on complete active space configuration interaction followed by a second order perturbation treatment (CAS-PT2). This surface was used for the evaluation of the two radiative associations rate constants by means of a quantum treatment of the collision between the interacting fragments.
Results. These calculations show unambiguously that HeH3+ is the most stable point on the corresponding global PES. Then, we determined the rate constants of the radiative associations HeH+ + H2 and He + H3+ leading to HeH3+.
Conclusions. Significative values were obtained that reach up to 2x10–18cm3/s, which should stimulate new tentatives to detect molecular helium in astrophysical objects.

Abstract Copyright: © ESO, 2017

Journal keyword(s): ISM: molecules - ISM: abundances - ISM: abundances

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 M 57 PN 18 53 35.0967659112 +33 01 44.883287544   15.405 15.769 15.901 16.062 DA(O?) 836 2
2 NGC 7027 PN 21 07 01.571952 +42 14 10.47120   10.358 8.831 10.157   ~ 2467 1

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