CONTROLLED CRYSTALLIZATION FROM SOLUTION AND 'IN SITU' BY IR-LASER: THE CIRCUMVENT OF PLASTIC PHASES. Roland Boese, Markus Nuesse, and Michael Nussbaumer Universitat-GH Essen, Germany

Two systems for crystallization are described: The 'in situ' crystallization device and an apparatus for a controlled cooling crystallization.

The 'in situ' crystallization device applies a focused infrared laser beam at the capillary which is cooled with an open gas stream on the diffractometer. The position of the heated (molten) zone and the intensity of the laser beam are computer controlled. This allows to grow single crystals from samples with very low melting points (e.g. gases at ambient) and to monitor the process with a video camera as well as by the diffraction pattern, ideally with a CCD detector. The device is suited to crystallize and sublime neat material in the capillary but also to crystallize from solution in order to circumvent plastic phases: The low temperature, ordered phase of norbornadiene is presented.

The second device is for the controlled crystallization by cooling of a solution and consists of two parts: A commercial particle counter using the scatter of laser light detects the number and size of the crystal seeds which emerge when cooling the solution. The computer-controlled warm-up and stopping of a stirring process then allows to observe the growing of the crystals at the bottom of a cuvette my means of a video camera. A series of pictures of a growing crystal while cooling slowly (e.g. 1deg. C per day) is assembled for a movie for observation of the process.