separation of the chlorine and bromine isotopes was not possible anymore. To obtain the momenta from the measured data, a mass of 35 amu was assumed for chlorine (as this isotope has a natural occurence of around 76 %) and a mass of 80 amu for bromine (as ${}^{79}$Br and ${}^{81}$Br occur in almost equal amounts). Again two peaks are visible, but at slightly different positions than before: along the $x$-axis, the peaks are close to zero, indicating that the CF${}_{n}^{+}$ fragment almost lies in a plane with the chlorine and bromine ion. The proton H${}^{+}$ is ejected mostly perpendicular to this plane.\
The procedure of applying constraints on the individual momenta should be employed with care as it might eliminate not only wrong mass assignments but also possible break-ups with different dynamics. In future experiments on isotope-containing species, the spectrometer design should be adjusted according to these findings.

Site-selective excitation
-------------------------

Most chiral molecules contain several carbon atoms. This raises the question if selective excitation at the stereocenter can be used to preferentially break its bonds and to yield fragments that allow determination of absolute configuration. In halothane, the inner shells of the carbon in the CF${}_{3}$ group (we 