Studies of cold chemistry in crossed and merged neutral beams

In this thesis we present the design of two setups to study low-energy collisions between neutral species: an electron velocity map imaging for chemi-ionisation reactions and a merged electrostatic guide for polar molecules scattering. In the past few years, chemi-ionisation of atoms and molecules by metastable He and Ne led to the measurement of the branching ratios between two possible reactive channels, namely Penning ionisation (PI) and Associative ionisation (AI). For molecular species, the reaction outcome is influenced by the redistribution of energy from vibrational excitation to translational energy. We designed an electron velocity map imaging spectrometer (e-VMI) to study chemi-ionisation of Kr, Ar, N2, H2 and D2 by metastable He(3S1) and Ne(3P2) atoms in a crossed beam setup. A curved magnetic hexapole was used to guide the metastable atoms, specifically selecting the He(3S1) and Ne(3P2) states. Collision energies of 60 meV were reached by individually controlling the velocities of both reactants. In these experiments, electron kinetic energy distributions obtained using the e-VMI spectrometer were related to state specific reaction products. Detecting electrons, which are released in the first reaction step, we could characterise the reaction encounter complexes. Merged beam experiments on neutral molecules allows molecular beam studies of reactive scattering below 1 K. We present the design and realization of a new merged beam setup that permits to study cold collisions between polar molecules, thus giving access to the investigation of dipole-dipole interactions in the sub-Kelvin range. The Stark effect was used to manipulate polar neutral molecules in an electrostatic guide. The electrodes structure required to merge two beams is highly complex and difficult to build by traditional methods. We used the 3D-printing metal coating approach, developed in our group, to realize a Y-shaped electrostatic guide in which two bent quadrupole guides are smoothly merging into a single hexapole guide. Simulations were performed to estimate the guide transmission as a function of the velocity in order to design the merged beams experiment. The correct functioning of the device was demonstrated by guiding ND3 molecules.