Chemiluminescence quasi-continua in collisions of Ca(1S), Sr(1S) and Mg∗(3P) atoms with I2 Original Research Article

Chemiluminescent reactions of magnesium, calcium, and strontium atoms with I2 were studied in a beam-gas configuration. For ground state atoms, unstructured chemiluminescence typical for alkaline earth dihalides MX2 was observed for Ca and Sr, but not for Mg. The emission extends from γ = 400 nm to γ > 950 nm. The pressure dependence of the chemiluminescence indicates that the MI2∗ molecules are formed mainly via vibrationally excited alkaline earth monohalide. Partial excitation of the atomic beams to the metastable 3P states brings as dominant emission a similar continuum-like spectrum for Mg∗ (the emitter is formed in a single collision), while for Ca∗ and Sr∗ the MI2∗ spectrum is suppressed by the chemiluminescence of alkaline earth monoiodides. A lower limit of chemiluminescence cross section for Mg∗(3P)+I2 is (4.2±0.9) × 10−20 m2 (corresponding to photon yield ⩾4.2% ± 0.9%), whereas for the other two reactive systems it is of the order of 10−21 m2 (photon yield 2~0.1%).