Crossed molecular beams kinetics: SnI and SnCl recoil velocity spectra from Sn+CH3I,n-C3H7I, and CCl4 and a lower limit for D(SnI)

Abstract

Laboratory (LAB) angular and time-of-flight (TOF) recoil velocity spectra of SnI and SnCl products formed by crossing an effusive Sn beam with CH3I, n-C3H7I, and CCl4 nozzle beams have been measured in a molecular beam apparatus equipped with an electron bombardment ionizer–quadrupole mass filter detector unit. Product center of mass (c.m.) recoil angle and energy distributions have been fit to the data by convoluting the c.m.→LAB transformation equations over measured speed distributions for both beams and the instrumental TOF response function. The Sn+CH3I and n-C3H7I reactions proceed via a direct interaction mechanism which favors scattering of SnI into the backward c.m. hemisphere (backward scattering denotes a reversal in Sn-atom direction during the reactive encounter). The SnCl from Sn+CCl4 is scattered predominantly sideways, probably also via a direct reaction mechanism. The Sn+CH3I reaction produces a more sharply backward peaked SnI c.m. product angular distribution with higher product recoil energies than does the Sn+n-C3H7I reaction. All of these reaction characteristics are strikingly similar to the best experimental information which is available for the analogous alkali atom reactions. Qualitative observations are also reported on the relative reactivities of Sn with CH3I,n-C3H7I, CCl4,i-C3H7I, CH3Br, CF3Br, C2Cl4, and SF6. A rigorous lower limit for the Sn–I bond energy is also established, D00(SnI) ?230 kJ/mole.