The most stable isomer of H2C4-(OCS)2 van der Waals complex: Theory and experiment agree on a structure with C2 symmetry

Abstract We report the infrared spectrum of H2C4-(OCS)2 trimer in the region of the ν1 fundamental vibration of the OCS monomer. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser. Both H2C4-(OCS)2 and D2C4-(OCS)2 are studied. Analysis of their spectra establishes that the trimer has C2 point group symmetry. Theoretical calculations performed to find stationary points on the potential energy surface confirm that the observed structure is the most stable form. The experimental rotational parameters are in very good agreement with those computed using double hybrid functionals.