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

Abstract

A pulsed negative ion source is described which combines supersonic beam expansion and laser-induced photoelectron emission from metal surfaces. Special features are supply of primary low-energy electrons in the high density region of the gas beam, stabilisation of negative ions by collisions and cooling of internal molecular motions. This gives rise to intense pulses of negative ions, which are opti mised for time-of-flight mass spectrometry. On the other hand, internal molecular cooling is optimal for negative ion spectroscopy, such as laser-induced photodissociation spectroscopy, photodetachment spectroscopy, negative ion photoelectron spectroscopy or negative ion zero kinetic energy (ZEKE) spectroscopy, providing information about negatively-charged as well as neutral molecular systems. Further advantages are large variability of the negative ion source, small physical extensions, or low demands on the vacuum system. In addition to the description of this negative ion source, mass spectra are presented as examples for application to molecular clusters, heterogeneous metal complexes, organic molecules with low vapour pressure or with environmental relevance, and molecular systems with importance in atmospheric chemistry.