Microwave andab initiostudies of the internal rotation of ethylene in the Ar-ethylene and Ne-ethylene van der Waals complexes

The Ethylene-Carbon Dioxide Complex and the Double Rotor Model

The infrared spectrum of the weakly bound C₂H₄-CO₂ complex is investigated in the region of the ν₃ fundamental band of CO₂ (≈2350 cm^-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The spacing of the various K-subbands in this perpendicular (ΔK = ±1) spectrum is very irregular, and the pattern of irregularity is quite different from that observed previously in another C₂H₄-CO₂ band by Bemish et al. [ J. Chem. Phys. 1995 , 103 , 7788 ]. But by allowing for the different symmetry of the ν₃ (CO₂) upper vibrational state, both results can be strikingly well explained using the "double internal rotor" model as described by Bemish et al.

Benchmark-Quality Semiexperimental Structural Parameters of van der Waals Complexes

Accurate data sets including noncovalent interactions have become essential for benchmarking computational methods. However, while there is much focus on obtaining an accurate description of relative energies, reliable prediction of accurate equilibrium geometries is also important. To facilitate the benchmarking of computed geometries, the current work includes an accurate data set of semiexperimental equilibrium geometries of noncovalent complexes that can be directly compared to ab initio data. The structures are based on high-accuracy spectroscopic data, combined with vibrational corrections at the double-hybrid density functional level. The current work is designed to complement available data sets of semiexperimental geometries of small rigid molecules and ab initio geometries of complexes. The benchmark-quality data comprises 16 complexes and includes dispersion interactions, hydrogen bonding, CH/π···π interactions, and trimers. In addition to the reference data, accurate counterpoise-corrected geometries have been obtained up to the CCSD level, along with interaction energies. A short overview of the performance of computational methods, including dispersion-corrected B3LYP and B2PLYP functionals, is also included.

Tunneling motions of argon on chlorofluoromethane

The rotational supersonic jet Fourier transform microwave spectra of the 35Cl and 37Cl species of the molecular complex chlorofluoromethane-argon show that, in its equilibrium conformation, the argon atom is located out of the ClCF plane, interacting with the F and Cl atoms. All rotational transitions are split into several quadrupole components, each of them further split into two lines, due to the tunneling motion of the Ar atom between two equivalent positions, below and above the ClCF plane. The feasible low energy pathway between the structurally degenerate conformations is described, in a first approximation, by a circular motion around the C-Cl bond, with barriers estimated to be about 61 and 100 cm(-1).