Absorption Spectra of Electrified Hydrogen Molecules

Molecular hydrogen normally has only weak, quadrupole transitions between its rovibrational states, but in a static electric field it acquires a dipole moment and a set of allowed transitions. Here we use published ab initio calculations of the static electrical response tensors of the H 2 molecule...

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Vydáno v:	The Astrophysical journal Ročník 932; číslo 1; s. 4 - 29
Hlavní autor:	Walker, Mark A.
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	Philadelphia The American Astronomical Society 01.06.2022 IOP Publishing
Témata:	Absorption Absorption spectra Angular momentum Astronomical data Astrophysics Diffuse interstellar bands Dipole moments Eigenvectors Electric fields Electrification Hydrogen Infrared spectra Internal conversion Interstellar chemistry Interstellar dust Interstellar dust extinction Interstellar line absorption Interstellar matter Interstellar medium Molecular physics Molecular spectroscopy Near infrared radiation Quadrupoles Tensors
ISSN:	0004-637X, 1538-4357
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Shrnutí:	Molecular hydrogen normally has only weak, quadrupole transitions between its rovibrational states, but in a static electric field it acquires a dipole moment and a set of allowed transitions. Here we use published ab initio calculations of the static electrical response tensors of the H 2 molecule to construct the perturbed rovibrational eigensystem and its ground state absorptions. We restrict attention to two simple field configurations that are relevant to condensed hydrogen molecules in the interstellar medium (ISM): a uniform electric field and the field of a pointlike charge. The energy eigenstates are mixtures of vibrational and angular momentum eigenstates so there are many transitions that satisfy the dipole selection rules. We find that mixing is strongest among the states with high vibrational excitation, leading to hundreds of absorption lines across the optical and near-infrared. These spectra are very different from that of the field-free molecule, so if they appeared in astronomical data they would be difficult to assign. Furthermore, in a condensed environment the excited states likely have short lifetimes to internal conversion, giving the absorption lines a diffuse appearance. We therefore suggest electrified H 2 as a possible carrier of the diffuse interstellar bands (DIBs). We further argue that in principle it may be possible to account for all of the DIBs with this one carrier. However, despite electrification, the transitions are not very strong and a large column of condensed H 2 would be required, making it difficult to reconcile this possibility with our current understanding of the ISM.
Bibliografie:	AAS33764 Interstellar Matter and the Local Universe ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14
ISSN:	0004-637X 1538-4357
DOI:	10.3847/1538-4357/ac68ee