Molecular Beam Deflection
Experimental Setup

The molecular beam apparatus we use is shown in fig. 1 and 2 in a photograph and as a scheme, respectively. It is composed of five sections which are marked as follows: A) cluster source, B) velocity measurement, C) beam shaping, D) deflection and E) detection.

Fig. 1: Photograph of the apparatus for molecular beam deflection experiments. The cluster source A) is located on the left side, the time-of-flight mass spectrometer E) is in the front on the right.
Fig. 1: Photograph of the apparatus for molecular beam deflection experiments. The cluster source A) is located on the left side, the time-of-flight mass spectrometer E) is in the front on the right.

In the laser vaporization source, a supersonic molecular cluster beam is generated with a broad size distribution of typically one to about 50 atoms. An important component of the cluster source is the cryogenic nozzle (A5), which thermalizes the clusters to any temperature between 30 and 450 K before expansion into high vacuum. The double skimmer unit (A6) and the two collimators (C1 and C2) are used for beam shaping. The velocity of the clusters can be measured with a self-built mechanical shutter (B1). The clusters then fly through the Stark electrodes (D1) and a Stern-Gerlach magnet (D2), whereby, depending on the experiment carried out, they undergo deflection by (D1) or (D2) perpendicular about their direction of flight. The clusters are then ionized by an F2 excimer laser (E2) and detected in a time-of-flight mass spectrometer (E4, E5). By scanning the molecular beam with a movable slit (E1), intensity profiles are determined with and without an electric or magnetic field simultaneously for all cluster species in the molecular beam. From this, the beam displacement and broadening as a result of the interaction with the electric or magnetic field can be quantified.

Fig. 2: Scheme of the apparatus for molecular beam deflection experiments.
Fig. 2: Scheme of the apparatus for molecular beam deflection experiments.

Literature

S. Schäfer, M. Mehring, R. Schäfer, P. Schwerdtfeger, Phys. Rev. A 2007, 76, 052515.

U. Rohrmann, S. Schäfer, R. Schäfer, J. Phys. Chem. A 2009, 113, 12115–12121.

U. Rohrmann, R. Schäfer, Phys. Rev. Lett. 2013, 111, 133401.