  A new instrument dedicated to the kinetic study of low-temperature gas phase
neutral-neutral reactions, including clustering processes, is presented. It
combines a supersonic flow reactor with Vacuum Ultra-Violet (VUV) synchrotron
photoionization time of flight mass spectrometry. A photoion-photoelectron
coincidence detection scheme has been adopted to optimize the particle counting
efficiency. The characteristics of the instrument are detailed along with its
capabilities illustrated through a few results obtained at low temperatures (<
100 K) including a {photoionization spectrum} of n-butane, the detection of
formic acid dimer formation as well as the observation of diacetylene molecules
formed by the reaction between the C$_2$H radical and C$_2$H$_2$.
