Probing the dependence of long-range, four-atom interactions on intermolecular orientation. 1. Molecular hydrogen and iodine monochloride

The dependence of the long-range interactions between molecular hydrogen and iodine monochloride on the geometry between the molecules is investigated. Laser-induced fluorescence and action spectroscopy experiments have identified multiple conformers of the o,/p-H₂...I^35,37Cl(X,v″:= 0) van der Waals complexes. A conformer with the hydrogen molecule localized at the iodine end of the dihalogen, most likely with C_2v, symmetry, is significantly more stable than an asymmetric conformer with the hydrogen localized in the well oriented orthogonally to the I-Cl bond axis, D ₀&Prime = 186.4(3) cm^-1 versus 82.8(3) ≤ D ₀″ ≤ 89.6(3) cm^-1. Complexes containing the 0-H₂(Z=1) species are more strongly bound than those with P-H ₂(Z=0). The electronically excited o,p-H₂⋯I ³⁵Cl(A,v́) and O,p-H₂⋯I^35,37C1(B, v́) complexes are found to have preferred asymmetric structures with binding energies bracketed between 73.7-80.5 and 69.5-76.3 cm^-1 for o-H₂⋯ I³⁵Cl(A,v́=23) and o-H ₂⋯I³⁵Cl(B,v́=3), respectively. Calculations of the H₂-I³⁵C1(B,v́=3) intermolecular vibrational energies and probability amplitudes undertaken using a scaled He + ICl(B,v́=3) potential enable us to make tentative assignments of the excited-state levels experimentally accessed.