Photoabsorption spectrum of helium trimer cation-Theoretical modeling

The photoabsorption spectrum of He+3 is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys.102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al. , [Mol. Phys.85, 243 (1995); Knowles et al. , Mol. Phys.87, 827 (1996)] whereas the model by Calvo et al. , [J. Chem. Phys.135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He+3 , for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He+2 . A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He+3 .Web of Science13920art. no. 20431

Joint experimental and theoretical study on vibrational excitation cross sections for electron collisions with diacetylene

We have measured and calculated differential and integral cross sections for elastic and vibrationally inelastic electron scattering by diacetylene molecules at electron energies from 0.5 to 20 eV in the whole range of scattering angles from 0 to 180°. The calculations were carried out using the discrete momentum representation method (DMR), which is based on the two-channel Lippmann–Schwinger equation in the momentum space. The interaction between the scattered electron and the target molecule is described by the exact static-exchange potential. Correlation–polarization forces are included by a local density functional theory. Energy dependences of integral and differential cross sections are presented for all nine vibrational modes. A detailed comparison of theoretical and experimental electron energy loss spectra is presented for electron energies of 1, 5.5, 10, and 20 eV. The theory assigns symmetry of resonances that could not be determined by empirical analysis alone. The theory reveals, and quantitatively describes, the switching of partial waves accompanying excitation of nontotally symmetrical vibrations. Limitations of the theory in reproducing experimental data for the narrow π* resonance below 2 eV are mentioned

A non-linear dissipative model of magnetism

International audienceA new non-linear dissipative model of magnetism based on the laws of statistical physics is presented. The linear response theory is extended to pass from a quasi-static dynamics to the actual dynamics. The non-equilibrium dissipative dynamics explicitly takes into account the relaxation phenomena as well as the jumps over the energy barriers. The approach provides kinetic equations analogous to the phenomenological laws of transport appearing in the extended thermodynamics. The model holds from molecular magnets possessing plateaus to bulk magnetic materials. An energetic and entropic analysis along the lines initiated by Jaynes and Prigogine provides a deeper understanding of the non-equilibrium thermodynamics

Theoretical modeling of ionization energies of argon clusters: Nuclear delocalization effects

Temperature dependence of vertical ionization energies is modeled for small argon clusters (N ⩽ 13) using classical parallel-tempering Monte Carlo methods and extended interaction models based on the diatomics-in-molecules approach. Quantum effects at the zero temperature are also discussed in terms of zero-point nuclear vibrations, either at the harmonic approximation level or at the fully anharmonic level using the diffusion Monte Carlo calculations. Both approaches lead to a considerable improvement of the theoretical predictions of argon clusters ionization energies and represent a realistic way of modeling of ionization energies for weakly bound and floppy complexes in general. A thorough comparison with a recent electron-impact experiment [O. Echt et al., J. Chem. Phys. 123, 084313 (2005)] is presented and a novel interpretation of the experimental data is proposed