Research Note

The hyperfine structure in the rotational spectrum of CF⁺

¹ IRAM, 300 rue de la Piscine, 38406 Saint-Martin d’Hères France
e-mail: guzman@iram.fr
² LUTH UMR 8102, CNRS and Observatoire de Paris, Place J. Janssen, 92195 Meudon Cedex, France
³ Institut für Physikalische Chemie, Universität Mainz, 55099 Mainz, Germany
⁴ LERMA – LRA, UMR 8112, Observatoire de Paris and École normale Supérieure, 24 rue Lhomond, 75231 Paris, France
⁵ Centro de Astrobiología, CSIC-INTA, Carretera de Ajalvir, Km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁶ European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 6 August 2012
Accepted: 1 November 2012

Abstract

Context. CF⁺ has recently been detected in the Horsehead and Orion Bar photo-dissociation regions. The J = 1−0 line in the Horsehead is double-peaked in contrast to other millimeter lines. The origin of this double-peak profile may be kinematic or spectroscopic.

Aims. We investigate the effect of hyperfine interactions due to the fluorine nucleus in CF⁺ on the rotational transitions.

Methods. We compute the fluorine spin rotation constant of CF⁺ using high-level quantum chemical methods and determine the relative positions and intensities of each hyperfine component. This information is used to fit the theoretical hyperfine components to the observed CF⁺ line profiles, thereby employing the hyperfine fitting method in GILDAS.

Results. The fluorine spin rotation constant of CF⁺ is 229.2 kHz. This way, the double-peaked CF⁺ line profiles are well fitted by the hyperfine components predicted by the calculations. The unusually large hyperfine splitting of the CF⁺ line therefore explains the shape of the lines detected in the Horsehead nebula, without invoking intricate kinematics in the UV-illuminated gas.