Laser-based ion source for mass spectrometry and laser spectroscopy of negative ions

A pulsed negative ion source is described which combines supersonic beam ex pansion and laser-induced photoelectron emission from metal surfaces. Speci al features are supply of primary low-energy electrons in the high density region of the gas beam, stabilisation of negative ions by collisions and co oling of internal molecular motions. This gives rise to intense pulses of n egative ions, which are optimised for time-of-flight mass spectrometry. On the other hand, internal molecular cooling is optimal for negative ion spec troscopy, such as laser-induced photodissociation spectroscopy, photodetach ment spectroscopy, negative ion photoelectron spectroscopy or negative ion zero kinetic energy (ZEKE) spectroscopy, providing information about negati vely-charged as well as neutral molecular systems, Further advantages are l arge variability of the negative ion source, small physical extensions, or low demands on the vacuum system. In addition to the description of this ne gative ion source, mass spectra are presented as examples for application t o molecular clusters, heterogeneous metal complexes, organic molecules with low vapour pressure or with environmental relevance, and molecular systems with importance in atmospheric chemistry.