Photochemical reactions in solution often proceed via competing reaction pathways comprising intermediates that capture a solvent molecule. A disclosure of the underlying reaction mechanisms is challenging due to the rapid nature of these processes and the intricate identification of how many solvent molecules are involved. Here combining broadband femtosecond transient absorption and quantum mechanics/molecular mechanics simulations, we show for one of the most reactive species, diphenylcarbene, that the decision-maker is not the nearest solvent molecule but its neighbour. The hydrogen bonding dynamics determine which reaction channels are accessible in binary solvent mixtures at room temperature. In-depth analysis of the amount of nascent intermediates corroborates the importance of a hydrogen-bonded complex with a protic solvent molecule, in striking analogy to complexes found at cryogenic temperatures. Our results show that adjacent solvent molecules take the role of key abettors rather than bystanders for the fate of the reactive intermediate.

Abstract. We have experimentally studied the diffusion thermopower of a serial double quantum dot, defined electrostatically in a GaAs/AlGaAs heterostructure. We present the thermopower stability diagram for a temperature difference T = (20 ± 10) mK across the device and find a maximum thermovoltage signal of several µV in the vicinity of the triple points. Along a constant energy axis in this regime, the data show a characteristic pattern which is in agreement with Mott's relation and can be well understood within a model of sequential transport.

Ultraviolet irradiation of a manganese-tricarbonyl CO-releasing molecule (CORM) in water eventually leads to the liberation of some of the carbon monoxide ligands. By ultraviolet pump/mid-infrared probe femtosecond transient absorption spectroscopy in combination with quantum chemical calculations, we could disclose for the exemplary compound [Mn(CO)3(tpm)](+) (tpm = tris(2-pyrazolyl)methane) that only one of the three carbonyl ligands is photochemically dissociated on an ultrafast time scale and that some molecules may undergo geminate recombination.

A comparative study is carried out on two spectroscopic techniques employed to detect ultrafast absorption changes in the mid-infrared spectral range, namely direct multichannel detection via HgCdTe (MCT) photodiode arrays and the newly established technique of chirped-pulse upconversion (CPU). Whereas both methods are meanwhile individually used in a routine manner, we directly juxtapose their applicability in femtosecond pump-probe experiments based on 1 kHz shot-to-shot data acquisition. Additionally, we examine different phase-matching conditions in the CPU scheme for a given mid-infrared spectrum, thereby simultaneously detecting signals which are separated by more than 200 cm −1 . References and links 1. P. Stoutland, R. Dyer, and W. Woodruff, "Ultrafast infrared spectroscopy," Science 257, 1913-1917 (1992). 2. P. Hamm, S. Wiemann, M. Zurek, and W. Zinth, "Highly sensitive multichannel spectrometer for subpicosecond spectroscopy in the midinfrared," Opt. Lett. 19, 1642Lett. 19, -1644Lett. 19, (1994. 3. P. Hamm, R. A. Kaindl, and J. Stenger, "Noise suppression in femtosecond mid-infrared light sources," Opt. Lett. 25, 1798Lett. 25, -1800Lett. 25, (2000. 4. G. Cerullo and S. D. Silvestri, "Ultrafast optical parametric amplifiers," Rev. Sci. Instrum. 74, 1-18 (2003). 5. J. Moore, P. Hansen, and R. Hochstrasser, "A new method for picosecond time-resolved infrared spectroscopy: applications to CO photodissociation from iron porphyrins," Chem. Phys. Letters 138, 110-114 (1987). 6. T. P. Dougherty and E. J. Heilweil, "Dual-beam subpicosecond broadband infrared spectrometer," Opt. Lett. 19, 129-131 (1994). 7. M. Lim, T. Jackson, and P. Anfinrud, "Binding of CO to myoglobin from a heme pocket docking site to form nearly linear Fe-C-O," Science 269, 962-966 (1995). Current and future archive for earth and planetary atmosphere studies," J. Quant. Spectrosc. Radiat. Transf. 109, 1043-1059 (2008). 38. M. Kaucikas, J. Barber, and J. J. van Thor, "Polarization sensitive ultrafast mid-IR pump probe microspectrometer with diffraction limited spatial resolution," Opt.

In the present study, the capabilities and limitations of surface light scattering (SLS) experiments in reflection geometry are investigated. Based on the study of the transparent reference fluid toluene at 303.15 K over a wide range of wave vectors between ( 0.3 a n d 6.6 ) × 1 0 5 m − 1 , the performance of two different detection schemes analyzing light scattered from the vapor–liquid interface in a perpendicular and non-perpendicular direction is assessed. Considering various aspects such as the quality of the heterodyne correlation functions, the input information for data evaluation, and the line-broadening effects, both detection schemes show comparable overall efficiency. For wave vectors larger than 4.5 × 1 0 5 m − 1 , where line-broadening effects are suppressed, the results obtained for liquid viscosity and surface tension agree with measurements in transmission geometry, validating the capability of the apparatus. For wave vectors smaller than 1.5 × 1 0 5 m − 1 , the SLS signals are distinctly affected by line-broadening effects, which will result in erroneous values for surface tension and in particular viscosity, even if empirical fitting approaches commonly used in literature are applied. The modeling of the influence of line broadening on the measurements results by a simple Gaussian-weighted sum of individual damped oscillations reveals the increasing complexity of the underlying wave vector distribution toward smaller wave vectors chosen for the scattering geometry.