The hyperfine structure in the rotational spectrum of CF+

TL;DR

This study calculates the hyperfine structure of CF+ and demonstrates that hyperfine splitting explains its double-peaked spectral lines in the Horsehead nebula, negating the need for complex kinematic explanations.

Contribution

The paper provides the first high-level quantum chemical calculation of CF+'s fluorine spin rotation constant and applies hyperfine fitting to observed spectra.

Findings

Hyperfine splitting of 229.2 kHz explains the double-peaked lines.

Hyperfine structure accounts for line profile without kinematic effects.

The method improves interpretation of CF+ spectral data.

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.