High‐Resolution Hydrogen Spectroscopy and The Proton Radius Puzzle

High resolution spectroscopy of the hydrogen atom takes on particular importance in the new SI, as it allows to accurately determine fundamental constants, such as the Rydberg constant and the proton charge radius. Recently, the second most precisely measured transition frequency in hydrogen, $1S?3S$, is obtained by our group. In the context of the Proton Radius Puzzle, this result calls for further investigation.     

Manipulation of Spontaneous Emission via Quantum Interference in an Elliptically Polarized Laser Field

Manipulation of spontaneous emission from an atom confined in three kinds of modified reservoirs has been investigated by means of an elliptically polarized laser field. Some interesting phenomena such as the multi-peak structure, extreme spectral narrowing, and cancellation of spontaneous emission can be observed by adjusting controllable system parameters. Moreover, these phenomena depend on the constructive or destructive quantum interference between multiple decay channels and which can be changed appreciably by varying the phase difference between the two circularly polarized components of the probe field. These results demonstrate the importance of an elliptically polarized laser field in controlling the spontaneous emission and its potential applications in high-precision spectroscopy.     

Size‐Dependent Structural and Optical Characteristics of Glucose‐Derived Graphene Quantum Dots

It is of scientific importance to obtain graphene quantum dots (GQDs) with narrow‐size distribution in order to unveil their size‐dependent structural and optical properties, thereby further to explore the energy band diagram of GQDs. Here, a soft‐template microwave‐assisted hydrothermal method to prepare GQDs with diameters less than 5 nm ± 0.55 nm is reported. The size‐dependent photoluminescence (PL) quantum yield (QY) decay lifetime and electron energy loss spectroscopy (EELS) of the GQDs are studied systematically. The QY of the GQDs with an average diameter of 2 nm is the highest (15%) among all the samples investigated and the QY decreases with increasing diameter of the GQDs. The size‐dependence of the PL decay lifetime is also observed. The result suggests that spatial confinement effects related to radiative relaxation play an important role in the size‐dependent decay lifetime. A realistic energy band diagram of the GQDs is deduced from the experimental results.     

Ab Initio Simulation of Charge Transfer at the Semiconductor Quantum Dot/TiO2 Interface in Quantum Dot‐Sensitized Solar Cells

Quantum dot‐sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next‐generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO₂ acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. To understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO₂ substrate are simulated using a rigorous ab initio density functional method. This method capitalizes on localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO₂ occurring via the strong bonding between the conduction bands of QDs and TiO₂ is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO₂ acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO₂ systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO₂ acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1 stretching band of GeD4

The high‐resolution stimulated Raman spectrum of the ν₁ band of GeD₄ with natural isotopic abundance germanium has been recorded. It has been analyzed as part of the ν₁/ν₃ stretching dyad. The ν₁ and ν₃ band centers have been deduced for all the isotopologues. Copyright © 2006 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of the 2ν10 overtone symmetric motion of C2H4

The high‐resolution stimulated Raman spectrum of the 2ν₁₀ band located at 1664.16 cm⁻¹ of C₂H₄ has been reanalyzed, thanks to the tensorial formalism developed in Dijon for X₂Y₄ asymmetric‐top molecules. A total of 191 lines were assigned and fitted as a single band without including perturbations such as Fermi or Coriolis coupling constants. We obtained a global root mean square deviation of 8.5 × 10⁻³ cm⁻¹. Further investigations are required to include interactions with the ν₂ and ν₇ + ν₁₀ bands. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of picosecond time‐resolved X‐ray absorption spectroscopy by high‐repetition‐rate laser pump/X‐ray probe at Beijing Synchrotron Radiation Facility

A new setup and commissioning of transient X‐ray absorption spectroscopy are described, based on the high‐repetition‐rate laser pump/X‐ray probe method, at the 1W2B wiggler beamline at the Beijing Synchrotron Radiation Facility. A high‐repetition‐rate and high‐power laser is incorporated into the setup with in‐house‐built avalanche photodiodes as detectors. A simple acquisition scheme was applied to obtain laser‐on and laser‐off signals simultaneously. The capability of picosecond transient X‐ray absorption spectroscopy measurement was demonstrated for a photo‐induced spin‐crossover iron complex in 6 mM solution with 155 kHz repetition rate.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1 band of osmium tetroxide

We present the first high‐resolution stimulated Raman study of osmium tetroxide (OsO₄). Lines from the ν₁ totally symmetric stretching fundamental have been assigned. These data together with the infrared assignments of the ν₃ band previously recorded (M. Louviot et al., J. Quant. Spectrosc. Radiat. Transfer, 2012, 113, 119–127) allowed a refinement of the analysis of the ν₁/ν₃ stretching dyad. We found that the ν₁ band has an unusual positive isotopic shift of approximately 0.32 cm^{− 1}/amu, which gives further evidence that the stretching dyad should be perturbed by a complex nearby bending band polyad. This work is part of a global effort to analyze all fundamental bands of OsO₄ to obtain a more precise experimental value of the ground state bond length for this heavy metal‐containing molecule. The result could serve as a benchmark for high‐level quantum chemistry calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1, 2ν1–ν1, ν2, 2ν2, and 3ν2–ν2 bands of CF4

The spectra of the ν₁, 2ν₁–ν₁, ν₂, 2ν₂, and 3ν₂–ν₂ bands of CF₄ were obtained with a quasi‐continuous wave stimulated Raman spectrometer. These five bands were studied at a temperature of 135 and 300 K (for the hot bands). The spectrum of ν₁ was obtained at a sample pressure of 2 mbar. For the spectra of the other regions, which are much weaker, higher pressures were used. The analysis has been performed thanks to the xtds and spview softwares developed in Dijon for such highly symmetric molecules. Combining the present results with a previous infrared study, we could determine a very accurate value for the C–F equilibrium bond length, i.e. r_e = 1.31588(6) Å. Copyright © 2013 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1/ν5 (C–H) stretching dyad of C2H4

The high‐resolution stimulated Raman spectra of the ν₁/ν₅ C–H stretching bands of C₂H₄ have been recorded and analyzed by means of the tensorial formalism developed in Dijon for X₂Y₄ asymmetric‐top molecules. A total of 689 lines (428 for ν₅ and 261 for ν₁) were assigned and fitted as a dyad including Coriolis coupling constants. We obtained a global root mean square deviation of 4.39 × 10^{− 3} cm^{− 1} (4.61 × 10^{− 3} cm^{− 1} for ν₁, 4.25 × 10^{− 3} cm^{− 1} for ν₅). The nearby 2ν₂ band, extrapolated from ν₂, was included in the analysis. However, no interaction parameter involving it could be fitted. The analysis is quite satisfactory, although some parts of ν₅ are not very well reproduced, probably indicating some yet unidentified resonances. This region is indeed quite dense, with many interacting dark states that cannot be included at present. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν2 and ν3 bands of C2H4

The high‐resolution stimulated Raman spectra of the ν₂ and ν₃ bands of C₂H₄ have been recorded and analyzed separately by means of the tensorial formalism developed in Dijon and Reims for X₂Y₄ asymmetric‐top molecules. For the ν₂ band, a total of 191 lines were assigned and fitted. We obtained a global root mean square deviation of 1.86 × 10^{− 3} cm^{− 1}. For the ν₃ band analyzed in interaction with the ν₆ infrared band, a total of 185 lines were assigned and fitted. We obtained a global root mean square deviation of 1.29 × 10^{− 3} cm^{− 1}. Both analyses lead to very satisfactory synthetic spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman spectroscopic studies of microstructure present in dipotassium molybdate crystals and their melts

Temperature‐dependent Raman spectra of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals up to and above their melting points were recorded, and their vibration modes in solid and molten states were assigned. Basic structural units and the corresponding cluster forms in molten dipotassium monomolybdates, dimolybdates, and trimolybdates were studied by in situ high‐temperature Raman spectroscopic studies together with theoretical calculations, including density functional theory and quantum chemistry ab initio calculation. Anion units of [MoO₄]²⁻, [Mo₂O₇]²⁻, and [Mo₃O₁₀]²⁻ were shown to principally exist in molten K₂MoO₄, K₂Mo₂O₇, and K₂Mo₃O₁₀, respectively. The mechanisms of the microstructural evolution of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals while being melted are schematically illustrated. Copyright © 2016 John Wiley & Sons, Ltd.