Extended basis CNDO calculations of linear and nonlinear electric susceptibilities of some molecular dianions and carbonions using coupled Hartree–Fock perturbation theory

The results of calculating the average polarizabilities, first and second hyperpolarizabilities and molar Kerr constants of C₅H, C₆H, 2-C₁₀H, 2-C₁₄H, C₈H and C₈H are reported. The main elements of our computational scheme are McWeeny's coupled Hartree–Fock perturbation theory and an extended basis CNDO wave function. It is shown that the studied anions have nonlinearities within the same order of magnitude as their respective uncharged parent molecules. The Kerr constants of these anions are analyzed and the contribution of the various terms is appraised.     

Remote sensing of the atmosphere using ultrashort laser pulses

Theoretical and experimental studies were performed on the propagation of ultrashort optical terawatt pulses through the atmosphere. Propagation simulations of intense sub-picosecond pulses show that non-linear processes, such as white light generation, can be initiated at a chosen distance by selecting an appropriate group velocity dispersion. With this technique, a white light continuum was generated in the atmosphere whose spectral distribution was characterised in the visible and near infra-red. Applications of this novel light source for atmospheric remote sensing were investigated, combining lidar and time-resolved broadband absorption spectroscopy techniques. Measurements were performed on the oxygen molecule and water vapour. A comparison between the experimental results and the tabulated spectroscopic data led to an excellent correlation with measurements made on water vapour whereas observations on the oxygen showed discrepancy. This study demonstrates that the remote generation of a white light source represents a new way to access the range-resolved multi-trace gas analysis in the atmosphere. Received: 8 December 1999 / Revised version: 18 May 2000 / Published online: 16 August 2000