Velocity map imaging (VMI) is used to study the dynamics of various dissociative electron attachment (DEA) processes by finding the kinetic energies and angular distri- bution of the products. In this project a VMI mass spectrometer was used as a Time of Flight Mass Spectrometer (ToFMS). ToFMS can be used to measure the absolute cross section of the ions. The voltage conditions for the best mass resolution was determined for electron impact ionization which produces positive ions, so that it could be used in similar conditions for the negative ions just by changing the polarity of the electric fields. A calibration of the spectrometer was also attempted to convert the time of flight of various ions to their m=q ratio. Then the spectrometer was studied in the VMI mode and optimized for best imaging conditions. Thus the spectrometer can be used both in ToFMS mode to get the absolute cross section and VMI mode to get angular distribution and K.E. of DEA.