Potential energy surface and infrared spectrum of the Ar–H2Cl+ ionic complex

Abstract

The infrared photodissociation spectrum of the Ar–H2Cl+ dimer has been recorded in the vicinity of the Cl–H stretch fundamentals of bare H2Cl+. Eleven Q branches of a strong perpendicular transition of a (near) prolate symmetric top are observed. The position and rotational structure of the band are consistent with an assignment to the free Cl–H stretch fundamental of a proton-bound Ar–HClH+ dimer. The global minimum on the intermolecular potential energy surface of Ar–H2Cl+, calculated at the MP2/aug-cc-pVTZ# level of theory, corresponds to the proton-bound structure with an intermolecular separation of Re=1.97 Å and a well depth of De=1860 cm−1. The slightly nonlinear ionic hydrogen bond is directional with large barriers (Vb) for internal rotation of H2Cl+ via planar transition states with C2v symmetry: Vb∼750 and 1330 cm−1 for the bridged (Re=3.45 Å, De=1107 cm−1) and chlorine-bound (Re=3.38 Å, De=531 cm−1) structures. The molecular constants of the observed transition, ν0=2663.1 cm−1 and A=10.35 cm−1, are in good agreement with the values calculated for the proton-bound equilibrium geometry, ν0=2665.4 cm−1 and Ae=10.28 cm−1.