Search results for "Laser Spectroscopy"
showing 10 items of 151 documents
Resonance laser ionization developments for IGISOL-4
2012
The work presented in this thesis concentrates on the development of the FURIOS laser ion source towards e cient and selective production of low energy radioactive ion beams. This includes design and development of the ion guide and hot cavity catcher systems for laser ion source use, and the development of in-source and in-jet laser spectroscopy techniques. The work has been carried out at the IGISOL facility in the Accelerator laboratory of the University of Jyväskylä. The FURIOS facility was upgraded and developed during the move to the IGISOL-4 facility. The laser transport was greatly improved in order to allow a large fraction of the initial laser intensity to be transported into the …
Relaxation Dynamics of Cr(acac)3 Probed by Ultrafast Infrared Spectroscopy
2007
Ultrafast infrared spectroscopy is used to probe the dynamics of Cr(acac)3 upon ligand field (400 nm) and charge transfer state (345 nm) excitation. At both pump wavelengths, the ground state absorption bands are strongly bleached at zero delay, and new broad transient absorption bands appear red shifted from the bleached bands. Recovery of ground state bleach is dominated by a fast time constant (15 ps), while a small percentage recovers within 760−900 ps. Despite the extensive studies on Cr(acac)3 photophysics, the fast recovery of the ground state as a major channel is reported here for the first time. As a general result, the present communication emphasizes the great value of ultrafast…
Time-Resolved Photochemistry of Stiffened Stilbenes
2019
Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/ Z mixtures of bis(benzocyclobutylidene) (t4, c4) and ( E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S
Photo-Induced Cluster-to-Cluster Transformation of [Au37–xAgx(PPh3)13Cl10]3+ into [Au25–yAgy(PPh3)10Cl8]+: Fragmentation of a Trimer of 8-Electron Su…
2021
We present the photoinduced size/structure transformation of [Au37-xAgx(PPh3)13Cl10]3+ (M37) into [Au25-yAgy(PPh3)10Cl8]+ (M25) cluster. Single-crystal X-ray diffraction revealed that M37 has a tri-icosahedron M36 metal core assembled via the fusion of three Au7Ag6 icosahedrons in a cyclic fashion and that the M36 core is further protected by phosphine and chloride ligands. The M37 cluster is found to be highly sensitive toward ambient light, and the M37 → M25 transition is observed with 530 nm irradiation, monitored by time-dependent UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and femtosecond transient absorption spectroscopy. Linear-response time-dependent DFT…
Regiochemical memory in the adiabatic photolysis of thymine-derived oxetanes. A combined ultrafast spectroscopic and CASSCF/CASPT2 computational stud…
2020
[EN] The photoinduced cycloreversion of oxetanes has been thoroughly investigated in connection with the photorepair of the well-known DNA (6-4) photoproducts. In the present work, the direct photolysis of the two regioisomers arising from the irradiation of benzophenone (BP) and 1,3-dimethylthymine (DMT), namely the head-to-head (HH-1) and head-to-tail (HT-1) oxetane adducts, has been investigated by combining ultrafast spectroscopy and theoretical multiconfigurational quantum chemistry analysis. Both the experimental and computational results agree with the involvement of an excited triplet exciplex(3)[BPMIDLINE HORIZONTAL ELLIPSISDMT]* for the photoinduced oxetane cleavage to generate(3)…
Self and N-2 collisional broadening of far-infrared methane lines measured at the SOLEIL synchrotron
2012
International audience; Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800 hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N-2 broadening coefficients of methane pure rotation lines have been measured in the 83-261 cm(-1) spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients h…
Charge injection and trapping at perovskite interfaces with organic hole transporting materials of different ionization energies
2019
The extraction of photogenerated holes from CH3NH3PbI3 is crucial in perovskite solar cells. Understanding the main parameters that influence this process is essential to design materials and devices with improved efficiency. A series of vacuum deposited hole transporting materials (HTMs) of different ionization energies, used in efficient photovoltaic devices, are studied here by means of femtosecond transient absorption spectroscopy. We find that ultrafast charge injection from the perovskite into the different HTMs (<100 fs) competes with carrier thermalization and occurs independently of their ionization energy. Our results prove that injection takes place from hot states in the valence…
Role of Shallow Electron Traps in the Fast Transient Optical Phenomena of Alkali Halide Crystals
2002
We present additional evidences that the same shallow electron traps-atomic alkali impurity centres [M + ] c 0 e - are responsible for both classes (A and B) of the transient IR-absorption bands: (A) bands with maximum at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps or bound polarons) and (B) bands with maximum at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, KBr:I, RbCl:I and RbBr:I (due to on-centre STE or on-centre STE localised at iodine dimer). Both classes of the IR bands have the same location, similar shape (both exactly coincide for KCl:I and KCl at 10 or 80 K), half-width, vibration structure. It is established that the same Mollwo-Ivey plot curves E o =a…
Transient absorption with a femtosecond tunable excitation pump reveals the emission kinetics of color centers in amorphous silica.
2021
We report a set of femtosecond (fs) transient absorption (TA) measurements following the dynamics of the so-called nonbridging oxygen hole center in silica, a model color center in wide bandgap amorphous solids, characterized by a very large Stokes shift between the UV excitation and its associated red emission at 1.9 eV. The changes in the TA spectrum were probed in the UV-visible range at various delays after photoexcitation and analyzed as a function of the UV excitation energy, in single-photon absorption conditions. The combination of the experiments helps to clarify the defect photocycle, highlighting how TA measurements with tunable UV excitation could represent a powerful tool to in…
Luminescence Center Excited State Absorption in Calcium and Zinc Tungsates
2002
The tungstate crystals are well known scintillators. The mechanism of luminescence center formation and the luminescence center model are under discussion today. The results of time-resolved spectroscopy of luminescence center in ZnWO4 and CaWO4 in wide temperature regions was presented. The luminescence and induced absorption under pulsed electron beam excitation (pulse duration 10 ns, 0.26 MeV) were studied. The experimental equipment used allows one to obtain the transient absorption spectra, luminescence decay kinetics and transient absorption relaxation times.