title: A new accurate ground-state potential energy surface of ethylene and predictions for rotational and vibrational energy levels.
abstract: In this paper we report a new ground state potential energy surface for ethylene (ethene) C2H4 obtained from extended ab initio calculations. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pVQZ was employed for computations of electronic ground state energies. The fit of the surface included 82,542 nuclear configurations using sixth order expansion in curvilinear symmetry-adapted coordinates involving 2236 parameters. A good convergence for variationally computed vibrational levels of the C2H4 molecule was obtained with a RMS(Obs.-Calc.) deviation of 2.7 cm(-1) for fundamental bands centers and 5.9 cm(-1) for vibrational bands up to 7800 cm(-1). Large scale vibrational and rotational calculations for (12)C2H4, (13)C2H4, and (12)C2D4 isotopologues were performed using this new surface. Energy levels for J = 20 up to 6000 cm(-1) are in a good agreement with observations. This represents a considerable improvement with respect to available global predictions of vibrational levels of (13)C2H4 and (12)C2D4 and rovibrational levels of (12)C2H4.
authors.affiliation: Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, BP 1039, F-51687, Reims Cedex 2, France.
authors.forename: Thibault
authors.initials: T
authors.lastname: Delahaye
authors.affiliation: Laboratory of Theoretical Spectroscopy, Institute of Atmospheric Optics, Russian Academy of Sciences, 634055 Tomsk, Russia and Quamer, State University of Tomsk, Russia.
authors.forename: Andrei
authors.initials: A
authors.lastname: Nikitin
authors.affiliation: Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, BP 1039, F-51687, Reims Cedex 2, France.
authors.forename: Michaël
authors.initials: M
authors.lastname: Rey
authors.affiliation: Institute of Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary.
authors.forename: Péter G
authors.initials: PG
authors.lastname: Szalay
authors.affiliation: Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, BP 1039, F-51687, Reims Cedex 2, France.
authors.forename: Vladimir G
authors.initials: VG
authors.lastname: Tyuterev