This thesis reports on the use of buffer gas cooling to produce slow and intense molecular beams, with the aim of creating a source of molecules that can be used to measure the electron electric dipole moment. A beam of Yb is extracted from a buffer gas cell by entrainment in a flow of helium. The beam is characterised and simulations are performed of the helium flow through the cell to better understand the effect this has on the beam characteristics. The velocity of the beam is found to vary between 65 m/s[superscript -1] and 204 m/s[superscript -1] depending on the helium flow through the cell, in agreement with the predictions of the simulations. The temperature of the beam is 2.4 K and the minimum divergence is 12°. The percentage of Yb that is extracted from the cell is ~10%.

Sources which use a pulsed valve to produce a supersonic jet are also characterised at cryogenic temperatures. The addition of a thermalisation cell is found to produce beams that are slower, colder and more intense. The peak beam intensity is 4.5×10[superscript 10] molecules per seradian per pulse, the velocity (206 ± 5) m/s and the translational temperature is (12.3 ± 0.5) K.

An electric decelerator is used to decelerate a pulse of YbF molecules from 300 m/s[superscript -1] to 276 m/s[superscript -1] by confining them to a travelling trap. Simulations of the molecules in the decelerator show that its acceptance is greater than those demonstrated previously. A detailed understanding of this deceleration is developed.

The Franck-Condon factors for the A[superscript 2]Π[subscript 1/2] (v = 0) − X[superscript 2]Σ[superscript +] (v - 0, 1, 2) transition of YbF are measured. The results show that, using three lasers, the molecule could be laser-cooled.