Crossed beams product angular distributions: MCl and MI from Ba, Sr, Ca, and Mg + ICl and BaCN and BaBr from Ba + BrCN

Abstract

Primitive product angular distributions of MCl and MI from Ba, Sr, Ca, and Mg+ICI and of BaCN and BaBr from Ba+BrCN have been measured in a crossed beams apparatus employing an electron bombardment ionizer-massfilter detector unit. Product center-of-mass (c.m.) recoil angle and energy distributions have been fit to the measured laboratory (LAB) angular distributions by averaging the c.m.→LAB transformations over the (nonthermal) beam speed distributions. Both the MCl and MI c.m. product distributions from M+ICl are relatively insensitive to the identity of the attacking atom, except that practically no MgI is formed in the Mg reaction. Other product yield ratios are estimated as ∼2:1 for MCl:MI from ICl, ∼10:1 for BaCN:BaBr from BrCN. All of the reactions favor forward c.m. product scattering (i.e., MX scattered within 90° of the direction defined by the incident M), although the preference is especially weak in the Ba+BrCN→BaBr+CN reaction. For ICl reactions, MI are formed with broader c.m. cross sections and higher average product recoil energies, E′, than are MCl; average E′ values are ∼8–12 kcal/mole for MI+Cl and ∼3–5 kcal/mole for MCl+I. The results are compared with the features of the analogous alkali atom reactions and are discussed in terms of the likely structures of the intermediates.