A microchannel-plate detector has been developed to detect the time and position of two particles simultaneously. High resolution in position and timing is achieved with 100 J.l-m FWHM and 0.5 ns FWHM, respectively. The detector is designed to measure dissociative processes of molecules in fast beams. The released kinetic energy and the direction of the associated momentum with respect to the beam direction in the center of mass can be determined directly. This method offers big advantages over the determination by means of a mass spectrometer which is common practice in the field of "translational spectroscopy." The efficiency is increased by a factor of 10 3 _10 5 with comparable energy resolution. Measurements are performed on the dissociative charge exchange of Hi with Mg atoms. In the range of 7.2-10.2 eV 17 discrete energies are observed due to the predissociation of the c 3 1Tu state in H2 and presumably also the c 11Tu state.

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We have studied the dissociation of HeH molecules produced in the charge exchange between fast HeH+ ions and Cs. The released kinetic energy is measured by detection in a delayed coincidence technique of the neutral He-H pairs formed after dissociation. First direct evidence is reported for quasibound, predissociative states of HeH with energy levels in agreement with theoretical predictions. HeH* molecules are formed with large rotational and little vibrational excitation. The decay mechanisms of the low electronic excited states of HeH are discussed.