Multiphoton laser ionization mass spectrometry of cesium iodide and atomic iodine

Using the technique of laser ionization mass spectrometry, a study of multiphoton ionization (MPI) of atomic iodine and cesium iodide was conducted with a tunable dye laser. One of the objectives was to determine if this technique provides more selective ionization of the components of such a mixture than does conventional electron bombardment. It was found that under intense photon irradiation, CsI fragments to I⁺ by a multistep process. The first step is dissociation of CsI which is followed by multiphoton ionization of the liberated atomic iodine. Because of this mechanism, the atomic iodine in a CsI + I mixture with less than 10% iodine cannot be detected by MPI at the available photon wavelengths (2800–3000 Å). However, operation at wavelengths which preclude dissociation of CsI should greatly improve the selectivity. The cross-section for two-photon excitation of iodine at 3047 Å was determined to be 4 × 10⁻⁵⁰ cm⁴ s⁻¹.