Multi-hit detector system for complete momentum balance in spectroscopy inmolecular fragmentation processes

A multi-hit detector system has been developed capable of measuring the com plete momentum vectors of all ionic fragments after the dissociation of com plex molecules induced by photon, electron or ion impact. The fragments are collected in an electrostatic held and detected with a position-sensitive micro-channel plate detector using a fast timing delay-line readout. The de tector has a position resolution better than 0.2 mm and can resolve fragmen ts with arrival times separated by at least 5 ns in time. We illustrate the features of this new detector with first measurements for the collision pr ocess He1+ + N-2 --> He-0 + N-p + Nq+ + (p + q - 1)e(-) and the complete mo mentum profile of all reaction products. A momentum resolution of 10 a.u. p erpendicular to the beam derived from the time-of-flight (TOF) and 20 a.u. perpendicular to the beam derived from the position on the detector have be en obtained using a room temperature target system for nitrogen molecules. An angular resolution of +/-5 degrees is obtained. (C) 1999 Elsevier Scienc e B.V. All rights reserved.