Abstract
The reactivity of Ca(1P1) with HCl, Cl2, and CCl4 has been studied as a function of Ca(1P1) alignment with respect to the initial average relative velocity vector of the reagents in a beam-gas scattering geometry. While the total chemiluminescence cross section for the Ca(1P1)+HCl reaction is insensitive to Ca(1P1) alignment, the branching into the CaCl(A 2Π) and CaCl(B2Σ+) states depends markedly on the approach direction of the atomic p orbital. Parallel approach of the Ca p orbital favors CaCl(B2Σ+) formation while perpendicular approach favors CaCl(A2Π). A weak dependence of these effects on CaCl(B2Σ+) vibrational state is observed. The analogous reaction with Cl2 shows a strong preference for perpendicular p-orbital approach in both chemiluminescent product channels, which is most prominant for the CaCl(A2Π) state. In contrast, the reaction with CCl4 displays no significant dependence on approach geometry. For Ca(1P1)+Cl2, a chemi-ionization channel is observed, showing a preference for perpendicular alignment intermediate between that for the CaCl(A2Π) and CaCl(B2Σ+) channels. Chemiluminescence spectra, absolute chemiluminescence cross sections, branching ratios, and emission polarizations are also presented. Results are interpreted in terms of an electron-jump model in which the symmetry of the reagents is preserved during a reactive encounter.
Published Version
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