Context : \mathrm { 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 \mathrm { CF ^ { + } } on the rotational transitions .

Methods : We compute the fluorine spin rotation constant of \mathrm { 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 \mathrm { CF ^ { + } } line profiles , thereby employing the hyperfine fitting method in GILDAS .

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

Conclusions :