A photoionization study of the van der Waals molecule C2H4 � HCl

Abstract

The dissociation energy of the C2H4 · HCl van der Waals complex was determined to be 3.18±0.73 kcal mol−1 by a dissociative photoionization technique. C2H4 · HCl was produced by free expansion of a 1:4 mixture of C2H4 in HCl and the clusters were ionized with tunable synchrotron radiation. The photoionization efficiency function of (C2H4 · HCl)+ from C2H4 · HCl was determined between 600 and 1,300 A and the onset for (C2H4 · HCl)+ was established as 1,163±2 A = 10.66±0.02 eV; these values give ΔHf0(C2H4 · HCl) = −10.7±0.7 kcal mol−1 and ΔHf0(C2H4·HCl+)=235.1±0.9 kcal mol−1. A complex ion dissociation energyD0(C2H4 · HCl+) = −0.3±0.9 kcal mol−1 was calculated from the results. The major features on the PIE curve for C2H4 · HCl+ can be analyzed in terms of the known energetic features of C2H4+ and HCl. An extended energy diagram for the C2H4 + HCl system is presented.