In which ionization method do gaseous ions primarily get produced by the application of photons?

The method in which gaseous ions are primarily produced by the application of photons is Atmospheric Pressure Photoionization (APPI). This technique utilizes ultraviolet (UV) light to ionize molecules within a sample, allowing them to be detected and analyzed in mass spectrometry.

In APPI, the interaction of UV photons with neutral molecules results in the ejection of an electron, creating positively charged ions. This process effectively enhances the ionization of various compounds, particularly those that are less amenable to ionization through other conventional techniques.

The efficiency of APPI is particularly pronounced with aromatic and unsaturated compounds, making it a valuable tool in fields such as environmental testing and pharmaceuticals. Its ability to work under atmospheric pressure conditions further facilitates streamlined sample introduction into mass spectrometric analyses.