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We report conclusive evidence of an efficient cooling mechanism via the electronic radiative transitions of hot small molecular anions isolated in vacuum. We stored C6(-) and C6H(-) in an ion storage ring and observed laser-induced electron detachment with delays up to several milliseconds. The terminal hydrogen atom caused a drastic change in the decay profiles. The decay of photoexcited C6H(-) is slow and nonexponential, which can be explained by depletion cooling, whereas that for C6(-) occurs extremely fast, on a time scale below 0.1 ms and can only be explained by electronic radiative cooling via low-lying electronic excited states.

Mid‐infrared spectroscopy is a useful tool for remotely sensing the composition of Earth and other planets. Quantitative mineralogical investigations are possible using remotely sensed data; however, the difficulty in modeling complex interactions of light with particles that are on the order of the wavelength limits the usefulness of the remote sensing data. As part of an effort to develop a more effective treatment of light scattering in planetary regolith, we explore the ability of T‐matrix and radiative transfer (RT) hybrid models to produce emissivity spectra that are consistent with laboratory measurements. Parameters obtained from T‐matrix calculations are used in three different RT models to construct emissivity spectra of enstatite particles of different sizes. Compared to the widely used Mie/RT hybrid models, the T‐matrix/RT hybrid models produce more consistent emissivity spectra for the finest particle size fraction (3.3 μm). Overall, T‐matrix hybrid models produce improved emissivity spectra, but larger particle sizes are still difficult to model. The improvement observed in T‐matrix/RT hybrid models is a result of the inclusion of multiple scattering in closely packed media, and it demonstrates the importance of the implementation of physically realistic factors in developing a more effective light scattering model for planetary regolith. Further development and implementation of this and similar hybrid models will result in an improvement in quantitative assessments of planetary particulate surfaces from mid‐infrared spectra.

The heat flux across the core-mantle boundary (Q CMB ) is the key parameter to understand the Earth's thermal history and evolution. Mineralogical constraints of the Q CMB require deciphering contributions of the lattice and radiative components to the thermal conductivity at high pressure and temperature in lower mantle phases with depth-dependent composition. Here we determine the radiative conductivity (k rad ) of a realistic lower mantle (pyrolite) 1 in situ using an ultra-bright light probe and fast time-resolved spectroscopic techniques in laser-heated diamond anvil cells. We find that the mantle opacity increases critically upon heating to ~3000 K at 40-135 GPa, resulting in an unexpectedly low radiative conductivity decreasing with depth from ~0.8 W/m/K at 1000 km to ~0.35 W/m/K at the CMB, the latter being ~30 times smaller than the estimated lattice thermal conductivity at such conditions 2,3 . Thus, radiative heat transport is blocked due to an increased optical absorption in the hot lower mantle resulting in a moderate CMB heat flow of ~8.5 TW, at odds with present estimates based on the mantle and core dynamics 4,5 . This moderate rate of core cooling implies an inner core age of about 1 Gy and is compatible with both thermally-and compositionally-driven ancient geodynamo. Main textHeat exchange rate between the mantle and core (Q CMB ) is of primary importance for mantle convection and core geodynamo, the two processes that have been paramount for life on Earth. Considerations of the mantle and core energy budgets suggest a Q CMB in the range of 10-16 TW (e.g. Ref. 5 ). Independently, transport properties of the mantle can provide insights into the Q CMB as it is controlled by the thermal conductivity of the mantle rock at the core-mantle boundary (CMB). Total thermal conductivity of primary lower mantle minerals is a sum of its lattice and radiative components (k total = k lat + k rad ). At near-ambient temperatures (T ~300 K) the dominant mechanism of heat conduction is lattice vibrations while radiative transport is minor. At high temperature, however, the radiative mechanism is expected to become much more effective 6 as ( , ) ~ ( , ) (Eq.1), where α(P,T) is the pressure-and temperaturedependent light absorption coefficient of the conducting medium. Mantle k rad is expected to increase with depth and light radiation might even be the dominant mechanism of heat transport in the hot thermal boundary layer (TBL) a few hundred km above the core 7,8 . To reconstruct mantle radiative thermal conductivity one needs to know the absorption coefficient of representative minerals in the near-infrared (IR) and visible (VIS) range collected at P-T along the geotherm.Light diffusion in the hot lower mantle is governed by absorption mechanisms in iron-