Photoelectric emission from the alkali metal doped vacuum-ice interface

The photoelectron photoemission spectra and thresholds for low coverages of Li and K adsorbed on water-ice have been measured, compared with photoionization spectra of the gas-phase atoms, and modeled by quantum chemical calculations. For both alkali metals the threshold for photoemission is dramatically decreased and the cross section increased on adsorption to the water-ice surface. Quantum chemical calculations suggest that the initial state is formed by the metal atoms adsorbed into the water-ice surface, forming a state with a delocalized electron distribution. This state is metastable and decays on the hundreds of seconds time scale at 92 K. The decay is markedly faster for Li than for K, probably due to diffusion into the ice film

Time resolved structural dynamics of butadiyne-linked porphyrin dimers

In this work the timescales and mechanisms associated with the structural dynamics of butadiyne-linked porphyrin dimers are investigated through time resolved narrowband pump / broadband probe transient absorption spectroscopy. Our results confirm previous findings that the broadening is partly due to a distribution of structures with different (dihedral) angular conformations. Comparison of measurements with excitations on the red and blue sides of the Q-band unravel the ground and excited state conformational re-equilibration timescales. Further comparison to a planarized dimer, through addition of a ligand, provide conclusive evidence for the twisting motion performed by the porphyrin dimer in solution

Photometry of comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact

The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur Astronomers) observing campaign is presented. The main goal was to perform an extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD R, I and narrowband aperture photometries were used to monitor the $Af\rho$ quantity. The observed behaviour showed a peak of 310 cm 83 days before perihelion, but we argue that it could be distorted by the phase effect, too. The phase effect is roughly estimated around 0.0275 mag/degree, but we had no chance for direct determination because of the very similar geometry of the observed apparitions. The log-slope of $Af\rho$ was around -0.5 between about 180--100 days before the impact but evolved near the steady-state like 0 value by the impact time. The DI module impact caused an about 60%{} increase in the value of $Af\rho$ and a cloud feature in the coma profile which was observed just after the event. The expansion of the ejecta cloud was consistent with a fountain model with initial projected velocity of 0.2 km/s and $\beta$=0.73. Referring to a 25~000 km radius area centered on the nucleus, the total cross section of the ejected dust was 8.2/$A$ km$^2$ 0.06 days after the impact, and 1.2/$A$ km$^2$ 1.93 days after the impact ($A$ is the dust albedo). 5 days after the event no signs of the impact were detected nor deviations from the expected activity referring both to the average pre-impact behaviour and to the previous apparitions ones.Comment: 25 pages (including cover pages), 9 figures, 1 table, accepted by Icarus DI Special Issu

Ultrafast Structure and Dynamics in the Thermally Activated Delayed Fluorescence of a Carbene-Metal-Amide

Thermally activated delayed fluorescence has enormous potential for the development of efficient light emitting diodes. A recently discovered class of molecules (the carbene – metal – amides, CMAs) are exceptionally promising as they combine the small singlet - triplet energy gap required for thermal activation with a large transition moment for emission. Calculations suggest that excited state structural dynamics modulate the critical coupling between singlet and triplet states, but do not agree on the nature of those dynamics. Here we report ultrafast time resolved transient absorption and Raman studies of CMA photodynamics. The measurements reveal complex structural evolution following intersystem crossing on the tens to hundreds of picoseconds timescale, and a change in the low frequency vibrational spectrum between singlet and triplet states. The latter is assigned to a change in frequency or amplitude associated with a Raman active mode localized on the metal centre

Vibronic interactions in the visible and near-infrared spectra of C60− anions

Electron-phonon coupling is an important factor in understanding many properties of the C60 fullerides. However, there has been little success in quantifying the strength of the vibronic coupling in C60 ions, with considerable disagreement between experimental and theoretical results. We will show that neglect of quadratic coupling in previous models for C60- ions results in a significant overestimate of the linear coupling constants. Including quadratic coupling allows a coherent interpretation to be made of earlier experimental and theoretical results which at first sight are incompatible

Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2

The first detected interstellar object 'Oumuamua that passed within 0.25au of the Sun on 2017 September 9 was presumably ejected from a stellar system. We use its newly determined non-Keplerian trajectory together with the reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past close encounters. Such an "encounter" could reveal the home system from which 'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90% confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249, 3.8Myr ago. Two more stars have encounter distances and velocities intermediate to these. The encounter parameters are similar across six different non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by scattering from a giant planet in one of the systems is plausible, but requires a rather unlikely configuration to achieve the high velocities found. A binary star system is more likely to produce the observed velocities. None of the four home candidates have published exoplanets or are known to be binaries. Given that the 7 million stars in Gaia DR2 with 6D phase space information is just a small fraction of all stars for which we can eventually reconstruct orbits, it is a priori unlikely that our current search would find 'Oumuamua's home star system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown dwarfs every Myr, the plausibility of a home system depends also on an appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa