The Internal Rotation in the $N_{2}O$-Ethylene Complex: Extraction of the Intermolecular Potential Energy Surface

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 Title: The Internal Rotation in the $N_{2}O$-Ethylene Complex: Extraction of the Intermolecular Potential Energy Surface Creators: Bemish, R. J.; Rhee, W. M.; Miller, R. E. Issue Date: 1995 Publisher: Ohio State University Abstract: In our preliminary analysis of the spectrum of the $N_{2}O$-Ethylene $complex^{1}$ correlating with the $\nu_{9}$ vibrational mode of the ethylene monomer, the results suggested that, unlike the analogous $CO_{2}$ complex which displays internal rotation, the complex was rigid. Nevertheless, there were several features of the spectrum that were inconsistent with a rigid structure. As a result, we have proceeded to record the spectrum associated with the $\nu_{1} + \nu_{3}$ mode of the $N_{2}O$. Analysis of both spectra leads to a structure that is stacked parallel with the $N_{2}O$ axis parallel to the carbon-carbon double bond and above the plane of the ethylene. It is now clear that the $\Delta K_{a}$ sub-band origins are shifted with respect to the rigid approximation, while the structure within each sub-band is well described by a rigid rotor Hamiltonian. This band shifting can be attributed to tunneling about the A inertial axis. Ab initio calculations performed for several geometries indicate that the only feasible rotation involves rotation of the $N_{2}O$ parallel to the plane of the ethylene. Imposing this constraint on the motion it is possible to solve the problem of a double rotor around a common axis to reproduce the pattern of $\Delta K_{a}$ origin shifts. The barrier to internal rotation was determined to be approximately $31 cm^{-1}$, five times larger than the iso-electronic $CO_{2}$-Ethylene complex. Description: 1. ""The Spectroscopy and Internal Tunneling Dynamics of the $C_{2}H_{4}-CO_{2}$ and $C_{2}H_{4}-N_{2}O$ Complexes: Two Distinctly Different Systems'', P.A. Block, Won Rhee and R.E. Miller, 49th International Symposium on Molecular Spectroscopy. Author Institution: URI: http://hdl.handle.net/1811/29890 Other Identifiers: 1995-TL-14