What are the different methods by which gases can be ionized?

Gas ionization processes are particularly important for mass spectrometry applications and the two primary methods involved here are electron ionization (EI) and chemical ionization (CI). read more

In chemical ionization, a reagent gas is injected first and subjected to electron bombardment to form charged species. This primary ion formation step leads to formation of more ions due to reactions between formed ions and neutral reagent gas molecules. The species thus formed now interact with the gas sample to ionize them. read more

Adiabatic ionization is a form of ionization in which an electron is removed from or added to an atom or molecule in its lowest energy state to form an ion in its lowest energy state. The Townsend discharge is a good example of the creation of positive ions and free electrons due to ion impact. read more

I can't find a really helpful link about how the ionization is produced, but the basic idea is fairly simple. The "positive ray" (which is itself a positive ion, of course) passes gas molecules and pulls of electrons by electrical interaction with the (negative) electrons of the gas molecules. read more