Design for improved resolution in a time-of-flight mass spectrometer using a supersonic beam and laser ionization source

Abstract

This article describes the design of a time‐of‐flight mass spectrometer (TOFMS) constructed for optimum use with resonance‐enhanced multiphoton ionization spectroscopy in supersonic beams. The use of the supersonic beam results in a great improvement in resolution, i.e., at least 800 at mass 93. Ion packets on the order of 10 ns FWHM or less are observed at our flat dual channel plate detector and the resolution ultimately appears to be laser‐pulse‐width limited. The design of this TOFMS utilizes fast‐pulsed molecular beam techniques to allow the use of reservoir pressures >1 atm with a large orifice (0.5 mm) in order to provide high on‐axis intensity for maximizing the photoionization signal produced by our pulsed laser system with the use of only modest pumping capacity. It also uses a skimmed beam, differential pumping, and a liquid‐N₂ baffle in order to maintain the flight tube at pressures on the order of 5×10⁻⁷ Torr and to eliminate organic contamination from the ionization region.