Negative ion adsorption by the ion source surface as a factor influencing ion lifetime measurements
Institute of Molecular and Crystal Physics, Ufa Research Center, Russian Academy of Sciences, prosp. Oktyabrya 151, Ufa, 450075, Russian Federation
It is well known that negative ions that form in the gas phase due to low-energy electron capture by molecules show a scatter in the measured lifetimes of their autodetachment states. In considering this problem, it is found that when using a static sector magnetic mass spectrometer, some of the ions that form on the ionization chamber walls are adsorbed and stabilized there and then join the registered ion flow, thereby distorting the measured lifetime. Because the number of the adsorbed ions depends on the experimental conditions, their contribution to the total flow is to some extent uncontrollable—hence the scatter.