An example system includes an electron ionization ion source and a mass analyzer. The electron ion source is configured, during operation of the system, to create from sample molecules a beam of ions extending along an ion beam axis. The system also includes a collision cooling chamber comprising a gas manifold and an electric field generator. The cooling chamber defines an entrance aperture and an exit aperture on respective opposing ends of the cooling chamber, the entrance aperture of the cooling chamber being in axial alignment with the ion beam axis. The cooling chamber is configured, during operation of the system, to generate a radio frequency (RF) field within the cooling chamber using the electric field generator, and receive collision gas through the gas manifold to pressurize the cooling chamber.