Post collision analyzer to study charge-exchange processes in ion-molecule collisions.

Abstract

We have designed an electrostatic charge state analyzer for ion beams having energies in the range of 5-20 keV/q. It is primarily built to investigate the different ionization processes involved in the slow (v < 1 a.u.) impact of highly charged ions on molecules. The analyzer is a cylindrical deflector analyzer (CDA) based on a pair of concentric cylindrical sectors of radii 110.2 and 95 mm, subtending an angle of 127° at its center. Additionally, an Einzel lens and a quadrupole deflector are deployed to focus and steer the ion beam. The compact design of the analyzer permits easy integration with an ion momentum spectrometer used for studying the fragmentation of the target molecules. The characterization of the CDA including its calibration and its transmission function is carried out using an ion beam delivered from an electron beam ion source. To check the performance of the setup, we have carried out experiments comprising the impact of Ar¹⁶⁺ projectiles on CO₂ target molecules at an energy of 18 keV/q. With the help of the CDA, different charge exchange ionization processes, such as single capture, double capture, and triple capture of electrons by the projectile ion have been separated efficiently. The possibility of a modification in the geometry of CDA is discussed to further improve its performance.