Design of Velocity Map Imaging Spectrometer Equipped with a Mass Gate Discriminating Particular Photofragments

Abstract EN

A photoionization spectrometer for velocity map imaging has been developed for measuring the scattering distribution of fragment ions from polyatomic molecules.

The spectrometer contains a mass gate and an ion reflector which are able to discriminate ions with a particular mass-to-charge ratio m/z.

The basic functions and feasibility of these devices were tested experimentally and theoretically.

First, the photoions from Kr and C60 were extracted into a time-of-flight (TOF) mass spectrometer by a transient or continuous electrostatic field.

When the pulse application on the mass gate was tuned to the arrival timing of ions with a specific m/z, the peak of the selected ions alone was present on a TOF spectrum.

Second, compatibility between velocity map imaging and ion discrimination was investigated by the computer simulations of the ion trajectories of photofragments from C60.

A pulsed voltage was applied to the mass gate synchronously with the arrival timing of C58+ ions.

The initial three-dimensional velocity distribution of C58+ was projected onto the image plane with an energy resolution better than 10 meV.

The C58+ image was free from the contamination of other ions such as C60+ and C56+.