A MASS SPECTROMETER WITH A LOW-TEMPERATURE IONIZATION CHAMBER TO STUDY HETEROGENEOUS REACTIONS OF ATOMS AND FREE RADICALS: EXAMPLE, IODINE ATOMS

Abstract

The main features of a mass spectrometer in which the ionization chamber can be cooled in a controlled way to the temperature of liquid nitrogen are given. Atoms or free radicals, formed in a heterogeneous quartz reactor that can be heated to 1000 °C, effuse through a small hole in the wall of this reactor and enter directly into the ionization chamber. With this instrument it is possible to study the various ways in which unstable particles disappear during collisions on a metallic surface maintained at low and controlled temperatures.The collision efficiency "b" of iodine atoms to form iodine molecules was found to vary between 1.7 × 10⁻³ and 4 × 10⁻³ on a surface at a temperature between +40 °C and −25 °C. Between−25 °C and −60 °C, the atoms are condensed at the same time as the iodine molecules; at lower temperatures, they are more "volatile" than iodine molecules, most of them colliding on the molecules of condensed iodine without reacting.