Max Planck Institutes and Experts

Intramolecular vibrational energy flow in bridged azulene-anthracene compounds is investigated by time-resolved spectroscopy. The bridges consist of molecular chains of the type (CH₂)_m with m ≤ 6 as well as (CH₂OCH₂)_n (n = 1,2) and CH₂SCH₂. With a short laser pulse excited molecules are formed where the excess vibrational energy is localised initially at the azulene side. The vibrational energy transfer through the molecular bridge to the anthracene side is followed by probing the energy content of the azulene and/or the anthracene chromophore with a second delayed laser pulse. The corresponding time constants τ_IVR for short bridges increase with the chain length. For longer bridges consisting of more than 3 elements, however, τ_IVR is constant at around 4-5 ps. Comparison with molecular dynamics simulations suggests that the coupling of these chains to the two chromophores limits the rate of intramolecular vibrational energy transfer. Inside the bridges the energy transport is essentially ballistic and, therefore, τ_IVRis independent on the length.

After the first successful tests of the mid-infrared interferometric instrument MIDI at the ESO Very Large Telescope at the end of 2002, the phase of Science Demonstration followed in the year under report. MIDI fully met the high expectations and thus opened up a new field of astronomical observations: for the first time a resolution of one hundredth of an arc second can be achieved in the mid-infrared spectral range. Observations of circumstellar disks around young stars as well as of the dust ring in the center of an active galaxy demonstrate the enormous power of the instrument. MIDI was built by a consortium of German, Dutch, and French teams under the leadership of MPIA.

If the dark matter in the universe consists of weakly interacting elementary particles that can annihilate each other, it should be possible to detect their annihilation radiation directly. High-resolution cosmological simulations of the distribution of dark matter in the Milky Way can be used to make detailed predictions for the expected annihilation radiation from the galactic center and the satellite galaxies of the Milky Way. If the dark matter particles are neutralinos, these predictions imply favourable detection possibilities for next generation gamma ray telescopes.

Scientists at the Max-Planck-Institute for Astrophysics in Garching and the University of Chicago have substantiated an explanation for the high space velocities of observed pulsars. Their computer models confirm the likely connection with asymmetries during supernova explosions.

The two NASA rovers "Spirit" and "Opportunity" are currently successfully exploring their landing sites Gusev crater and Meridiani Planum on Mars. On board are two Alpha-Particle-X-ray-Spectrometers (APXS), which determine in-situ the chemical and mineralogical composition of rocks and soils. The chemistry of the analyzed surfaces clearly provides evidence for a water-rich past on planet Mars. The volcanic rocks at Gusev crater are covered by a rind and are penetrated by veins that are enriched in elements, e.g., sulfur, chlorine and bromine, which occur as anions in water. The chemistry of the old rocks at the Columbia Hills is altered to such an extent that their indigenous composition is difficult to deduce. The Meridiani Planum landing site exhibits bedrocks which consist of sulfates of up to 40 percent by weight. They were possibly deposited under conditions similar to those encountered presently in desert areas of the Earth.