B. Pranszke

Steric effects in chemiluminescent reactions of metastable Ca∗, Sr∗ atoms with isomeric propyl halides

Abstract Reactions of metastable alkaline earth atoms with normal and branched propyl halides were studied in a beam-gas arrangement. Chemiluminescence spectra of alkaline earth monohalides were observed for calcium and strontium reactions. Some differences in the CaX ( B 2 Σ + / A 2 Π ) branching ratio were found with isomeric variation of the targets. Total collision cross-sections for Mg ∗ and Ca ∗ reactions are independent of the isomeric substitution; for strontium the values for isopropyl iodide are 50% higher than those for normal propyl iodide target. Differences in chemiluminescence cross-sections are found for reactions of calcium with propyl iodides and propyl chlorides.

Electronic branching ratios in the chemiluminescent reactions of Ca(1S) and Ca∗(3P) with ICl and IBr

Abstract Chemiluminescence of calcium monohalides formed in the reactions of ground state Ca(1S) and metastable Ca∗(3P) atoms with ICl or IBr was studied in a beam-gas arrangement. Total collision and chemiluminescence cross sections were measured to estimate photon yields of electronic states of the products. For the (A2Π+B2Σ+) states, aggregate yields appear to be arithmetic averages of the values for proper homonuclear halogen targets and branching ratios are in agreement with prior expectations. The experiment gives lower limits of the dissociation energies: D0(CaBr) ⩾ 353 kJ/mol and D0(CaI) ⩾293 kJ/mol.

ELECTRONIC BRANCHING RATIOS IN THE CHEMILUMINESCENT REACTIONS OF SR(1S) AND SR*(3P, 1D) ATOMS WITH ICL AND IBR

The chemiluminescence of strontium monohalides formed in the reactions of ground state Sr(5s21S) and discharge-excited metastable Sr∗(5s5p 3P, 5s4d 1D) atoms with ICl and IBr was studied in a beam-gas arrangement. For the Sr(1S) reactants, only strontium monochloride and monobromide emission could be observed; the latter indicates that D0(SrBr) ⩾ 336 kJ/mol. Collisions of metastable strontium atoms with the interhalogens produced both monohalides in the A2Π, B2Σ+and C2Π states. The electronic branching ratios have been determined with relatively high precision, but absolute values of chemiluminescence cross sections have not been measured. The branching into the (A + B) exit channels of chemically different strontium monohalides was found to be statistical, while for the C states it shows a deviation.

Cross sections for the collisions of metastable Mg*(3P) and Ca*(3P,1D) atoms with HX molecules (X = F, Cl, Br, I)

Collisions of the metastable Mg*(3P) and Ca*(3P, 1D) atoms with HF, HCl, HBr, and HI molecules have been studied in a beam-gas arrangement. The total collision cross section were determined from the attenuation of spectral lines emitted by the metastables and when possible from the dependence of chemiluminescence intensity on target gas pressure. The total cross sections for Mg*, Ca* + HC1, HBr, and HI are rather large and indicate harpooning mechanism. The Mg* reactions with HX give no electronic chemiluminescence while the Ca* +HX reactions produce electronically excited CaX* radicals for all HX targets studied. For the latter reactions electronic chemiluminescence cross sections and photon yields were determined.

Electronic energy partitioning in the reactions of metastable Mg*(3P) and Ca*(3P,1D) atoms with halogenated methanes CX4 (X = F, Cl, Br)

Collisions of metastable Mg*(3P) and Ca*(3P, 1D) atoms with CF4, CCl4, and CBr4 were studied in a beam-gas arrangement. The total attenuation cross sections determined for the reactive systems vary in a wide range increasing with electron affinity of the target gas. The reactions of metastable Mg*(3P) with CX4 yield no chemiluminescence. All Ca* + CX4 reactions give electronically excited CaX* products and the chemiluminescence yield increases with reaction exo-ergicity.