Search

The results of an SCF/SDCI treatment are presented for selected portions of the ground state potential energy surface for the Cu3 molecule. For equilateral triangle geometries (D3h) the lowest state is 2E’ arising from 4sa’214se’1. The 2E’ state exhibits strong Jahn–Teller distortion, leading to 2A1 (acute angle) and 2B2 (obtuse angle) minima in C2v symmetry. Here the 2B2 minimum is a true minimum on the surface while the 2A1 minimum is a saddle point or very shallow secondary minimum connecting adjacent 2B2 minima. This strong Jahn–Teller distortion is consistent with the observed ground state vibrational levels in the gas phase spectroscopic studies of Morse, Hopkins, Langridge-Smith, and Smalley and in the matrix Raman studies of Moskovits. The 2B2 minimum is also consistent with the observed ESR spectrum of Cu3 in a matrix, which has been interpreted as an obtuse angle structure with most of the spin density on the end Cu atoms. A linear 2Σ+u state is found to be 0.26 eV higher. Two possible candidates have been found for the upper state in the spectrum of Morse et al. (i) a 3s Rydberg state of 2A1 symmetry and (ii) a 3d→4s state of 2E‘ symmetry. Both of these states are consistent with the observed selection rules. The 2E‘ state would be expected to be weakly Jahn–Teller distorted in agreement with the fit to the upper state levels by Morse et al. and by Thompson, Truhlar, and Mead. [ABSTRACT FROM AUTHOR]

We have examined the structure, torsional potentials, vibrational spectra, and harmonic force fields for the s-cis and s-trans isomers of methacryloyl fluoride with the aim of understanding some of the conformational properties of these molecules and their relationship to macroscopic polymer properties. The calculations have been performed at the SCF level with a split valence basis set. We find the structure to be in reasonably good agreement with experiment and as expected find the structural variations between the two isomers to be slight. However, we do suggest a reexamination of the carbonyl geometry in light of our studies. Our calculations show the energy difference between the s-cis and the s-trans isomers to be less than 1 kcal/mol at both the split valence and the split valence polarized levels, favoring the s-trans form. An examination of the torsional potential reveals that a rigid rotor approximation provides an adequate description of the motion of either the methyl group, or of the COF moiety. For the methyl group we find a barrier of 1.5 kcal/mol, with the preferred conformation having the hydrogen atom eclipsed with respect to the carbon–carbon double bond. Our best calculations show that the torsional barrier to interconvert the s-trans to the s-cis form is 7.0 kcal/mol, somewhat higher than the recent experimental values of 6.5 and 5.1 kcal/mol. This study also points out the need to include the difference in zero point energies between reactants and the transition state when evaluating torsional potentials. Our calculated vibrational spectra show the similarities and differences between these two isomers, and suggest areas where the assignments should be further examined. In particular, we suggest that some of the low frequency torsional modes deserve further scrutiny. A fit of our data to a three term Fourier series shows that we are able to reproduce the experimentally derived barrier, even though a direct determination shows that... [ABSTRACT FROM AUTHOR]

An ab initio study that includes relativistic effects via first-order perturbation theory and correlation effects using the coupled pair functional formalism is presented for the ground state surface of Cu3. An analogous calculation is presented for the 1Σ+g ground state of Cu2 for calibration. The ground state of Cu3 is found to be a 2B2 state corresponding to a Jahn–Teller distortion (R=4.396 a0, θ=64.5°) of a 2E’ equilateral triangle geometry. This structure is found to lie 59 cm-1 below the 2A1C2v geometry and 280 cm-1 below the D3h equilateral geometry in good agreement with the pseudorotation barrier and Jahn–Teller stabilization energy deduced by Truhlar and Thompson from analysis of the fluorescence spectrum of Rohlfing and Valentini. [ABSTRACT FROM AUTHOR]