A velocity map imaging spectrometer for electron–ion and ion–ion coincidence experiments with synchrotron radiation

We have built a velocity map imaging (VMI) spectrometer optimized for angle-resolved photoionization experiments with synchrotron radiation (SR) in the VUV and soft X-ray range. The spectrometer is equipped with four electrostatic lenses that focus the charged photoionization products onto a position-sensitive multi-hit delay-line anode. The use of two additional electrostatic lens elements as compared to the standard design of Eppink and Parker [A.T.J.B. Eppink, D.H. Parker, Rev. Sci. Instr. 68 (1997) 3477] provides better focusing of an extended interaction region, which is crucial for most SR applications. Furthermore, the apparatus is equipped with a second micro-channel plate detector opposite to the VMI spectrometer, enabling electron–ion coincidence experiments and thereby mass-resolved ion spectroscopy independent of the time structure of the synchrotron radiation. First results for the photofragmentation of CO2 molecules are presented.