A time-of-flight mass spectrometer for large molecular clusters produced in supersonic expansions

Abstract

Supersonic free jet expansions are often used to produce beams of cold molecules and clusters. They are an essential part of laser vaporization cluster sources, where small particles of a material are seeded within a helium carrier gas during the expansion. These sources accelerate the clusters to the thermal velocity of the helium gas used in the generation process. By tilting the acceleration grids in a time-of-flight spectrometer, the initial velocities of molecular clusters transverse to the flight path can be selectively reduced to zero, allowing for a less off-axis flight path and permitting detection of higher mass clusters than is possible with conventional post-acceleration deflection schemes. Mass-resolved spectra of ions larger than 27 000 amu have been obtained using this scheme.