title: Determination of the ortho to para ratio of H2Cl+ and H2O+ from submillimeter observations.
abstract: The opening of the submillimeter sky with the Herschel Space Observatory has led to the detection of new interstellar molecular ions, H2O(+), H2Cl(+), and HCl(+), which are important intermediates in the synthesis of water vapor and hydrogen chloride. In this paper, we report new observations of H2O(+) and H2Cl(+) performed with both Herschel and ground-based telescopes, to determine the abundances of their ortho and para forms separately and derive the ortho-to-para ratio. At the achieved signal-to-noise ratio, the observations are consistent with an ortho-to-para ratios of 3 for both H2O(+) and H2Cl(+), in all velocity components detected along the lines-of-sight to the massive star-forming regions W31C and W49N. We discuss the mechanisms that contribute to establishing the observed ortho-to-para ratio and point to the need for a better understanding of chemical reactions, which are important for establishing the H2O(+) and H2Cl(+) ortho-to-para ratios.
authors.affiliation: LERMA, Observatoire de Paris , ENS, and UMR8112 du CNRS, 24 rue Lhomond, Paris 75231 cedex 05, France.
authors.forename: Maryvonne
authors.initials: M
authors.lastname: Gerin
authors.forename: Massimo
authors.initials: M
authors.lastname: de Luca
authors.forename: Dariusz C
authors.initials: DC
authors.lastname: Lis
authors.forename: Carsten
authors.initials: C
authors.lastname: Kramer
authors.forename: Santiago
authors.initials: S
authors.lastname: Navarro
authors.forename: David
authors.initials: D
authors.lastname: Neufeld
authors.forename: Nick
authors.initials: N
authors.lastname: Indriolo
authors.forename: Benjamin
authors.initials: B
authors.lastname: Godard
authors.forename: Franck
authors.initials: F
authors.lastname: Le Petit
authors.forename: Ruisheng
authors.initials: R
authors.lastname: Peng
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Phillips
authors.forename: Evelyne
authors.initials: E
authors.lastname: Roueff