The optimal structures and harmonic vibrational frequencies of cyclic water clusters, (H2O)n, have been determined at the Hartree–Fock (for n=2–6) and second order perturbation theory (for n=2–4) levels of theory with an augmented correlation consistent double zeta basis set At the MP2 level this basis set yields very accurate results for the structure, dipole moment, and polarizability of the water monomer as well as results of comparable accuracy for the structure, binding energy, and harmonic vibrational frequencies of the water dimer The optimal structure of (H2O)4 and the harmonic frequencies of (H2O)3,4 are the first ones reported at a correlated level for these species Analysis of the structural trends reveals that the separation between neighboring oxygen atoms decreases exponentially with increasing cluster size The predicted R0(O–O) for the ring hexamer is less than 002 A shorter than the interoxygen separation in ice Ih Furthermore, the trends in the harmonic vibrational frequencies sugge

Ab initio studies of cyclic water clusters (H2O)n, n=1–6. I. Optimal structures and vibrational spectra

The current state of the theory and its application to low-energy electron-molecule collisions is reviewed. The emphasis is on elastic scattering and vibrational and rotational excitation of small diatomic and polyatomic molecules. New and traditional theoretical approaches are described, and the results of calculations are compared with existing experimental measurements.

The theory of electron-molecule collisions

In organics-based (opto)electronic devices, the interface dipoles formed at the organic/metal interfaces play a key role in determining the barrier for charge (hole or electron) injection between t ...

Characterization of the Interface Dipole at Organic/ Metal Interfaces

http://bromine.cchem.berkeley.edu/grppub/dan5.pdf

Anion spectroscopy of uracil, thymine and the amino-oxo and amino-hydroxy tautomers of cytosine and their water clusters

Differential scattering experiments with the crossed-beam method have been performed to study vibrational excitation of HF and HCl by electron impact at very low collision energies. The excitation functions for nu =1 and nu =2 have been measured from threshold to some eV above. In each case, an unusually strong and sharp threshold peak is observed with a broad resonance region following thereafter. The absolute cross sections reach values of the order of 10-15 cm2 for the threshold peaks in the nu =1 channel. The angular distributions are isotropic in the whole resonance region. The threshold resonances are interpreted as quasi-bound 2 Sigma + states in the dipole field possibly correlated with H*+X-. The broad resonance region is attributed to a very short-lived resonance state which may be the HX- 2 Sigma + state correlated with ground-state fragments H+X-.

Vibrational excitation of polar molecules by electron impact. I. Threshold resonance in HF and HCl

The influence of a molecule's dipole moment on its ability to capture an electron into a stable bound state is examined. It is proved that, in the fixednuclei approximation, a value greater than 1·625 Debye for the dipole moment suffices to guarantee the existence of a discrete spectrum of negative ion states. Implications for Hartree-Fock calculations of negative ions are discussed. The interaction of electronic, vibrational and rotational motions in negative dipolar ions is studied, and conclusions are drawn for real molecules.

Negative ions of polar molecules

The collision frequencies of thermal electrons in polar gases are investigated. A quantitative discussion is given of the approximations contained in the conventional theory and it is argued that the ‘exact elastic scattering approximation’ of Mittleman and von Holdt is not a valid description. An error in the comparison of theory and experiment is corrected and it is suggested that the discrepancies can be largely attributed to omitted terms in the assumed interaction potentials. A modified formula is presented for the drift velocity of thermal electrons moving in molecular gases under the influence of a small electric field, which takes account of the internal structure of the molecules.

Electron collision frequencies in polar gases

The spin and space symmetry of negative ions of polar molecules are studied. It was previously known that a dipole moment exceeding 1·625 debye is a sufficient condition for the existence of the corresponding ion. It is shown that such an ion has the same space symmetry in its electronic wavefunction as does the neutral molecule. Additional negative ion states of one or more other symmetries exist if the molecule has a symmetry axis or plane, and has a dipole moment exceeding 9·638 debye. The above results are proven in the approximation that the nuclei are held stationary.

Oakley H. Crawford

Papers

Negative ions of polar molecules

Electron collision frequencies in polar gases

Symmetry of negative ions of polar molecules