Development of High-Resolution Photoelectron Imaging with Dual-Reflection Time of Flight Mass Analyzer^†

A velocity map imaging photoelectron spectroscopy, coupled with an electrospray ionization source and a dual-reflection time of flight (TOF) mass analyzer has been developed for the investigation of anions in the gas phase. Anions formed in the electrospray source are guided by a radio-frequency quadrupole ion guide into a quadrupole ion trap, where the ions are accumulated. A unique feature of this apparatus involves the coupling of a dual-reflection mass analyzer to the original Wiley-McLaren design. This can effectively improve the mass spectrum resolution, so as to accurately select the target ion. The mass resolution (M/ΔM) above 2000 can be achieved. The velocity map imaging spectrometer resolution is about 5.8 meV full width at half maximum for the photoelectrons with the kinetic energy of 0.59 eV, leading to a relative resolution of ~0.98%. The detailed design, construction, and operation of the new apparatus are presented.