Femtosecond spectroscopy allows us to follow the motion of a wavepacket prepared by an ultrashort laser pulse on the excited-state potential energy hypersurface through the conical intersection (CoIn) mediating the radiationless transition from the excited state (usually S1) to the ground state (S0). The quantum yields for photoproduct formation and radiationless electronic deactivation are decided by the dynamics of the wavepacket in the vicinity of the CoIn. Our major research themes "Photostability of the DNA and its Building Blocks" and "Dynamics of Functional Photochromic Molecular Switches" are therefore closely related.
Wavepacket motion on the excited potential energy hypersurface through the conical intersection
(CoIn) connecting the excited state (S1) with the ground state (S0). (c) F. Temps
In ideal cases, the experimentally observed dynamics can be directly assigned to the motion of specific atoms or functional groups in a molecule (e.g. hexa- and pentafluorobenzene).
TOF-MS and photoelectron imaging
Femtosecond time-resolved ion yield spectroscopy (fs-IYS) and photoelectron imaging spectroscopy (fs-PEIS) in combination are probably the most powerful tools to probe the ultrafast dynamics of molecules in excited electronic states.
Coherent oscillation due to an out-of-plane vibrational motion in the femtosecond
ion yield spectrum of hexafluorobenzene (HFB) after femtosecond laser excitation
to the ππ* state at λ = 260 nm. (c) H. Studzinski, F. Temps
Femtosecond time-resolved PEIS, in particular, allows one to follow ultrafast radiationless transitions in a photo-excited molecule from the initial optically bright state to lower-lying optically dark states, which cannot easily be identified by other means. We apply this method to idealized model compounds to elucidate basic photo-induced dynamics in organic chromophores. Interesting examples are hexa- and pentafluorobenzene, model compounds for DNA bases, diazocine, and sunscreen molecules.
- H. Studzinski, S. Zhang, Y. Wang, F. Temps, "Ultrafast Non-Radiative Dynamics in Electronically Excited Hexafluorobenzene by Femtosecond Time-Resolved Mass Spectrometry", J. Chem. Phys. 128, 164314 (2008).
Femtosecond Fluorescence Up-Conversion (FLUpCon) spectroscopy is indispensible for the elucidation of complex ultrafast photophysical and photochemical transformations because of its direct sensitivity to the lifetime of the optically bright photo-excited state(s) reached in an experiment. Thanks to meticulous suppression of scattered light, our FLUpCon setup is unusually sensitive. It is also our easiest-to-operate femtosecond experiment. It can in fact readily be operated by a student for her/his Bachelor Thesis.
Schematic experimental setup for femtosecond fluorescence up-conversion. (c) F. Temps
For molecules showing pronounced spectro-temporal evolution of the fluorescence, due to change of Franck-Condon overlap, molecular structure, or solvation dynamics, we also operate a Kerr-gated broadband fluorescence spectrometer.
- J. Bahrenburg, F. Renth, F. Plamper, W. Richtering, F. Temps, "Femtosecond Spectroscopy Reveals Huge Differences in the Photoisomerization Dynamics of Azobenzenes Linked to Polymers and Azobenzenes in Solution," Phys. Chem. Chem. Phys.16, 11549 - 11554 (2014). DOI: 10.1039/C4CP01196A
- N. K. Schwalb, F. Temps, "A Modified Four-State Model for the 'Dual Fluorescence' of N6,N6-Dimethyladenine derived from Femtosecond Fluorescence Spectroscopy", J. Phys. Chem. A 113, 13113 – 13123 (2009). DOI: 10.1021/jp9021773
- T. Pancur, N. K. Schwalb, F. Renth, F. Temps, "Femtosecond Fluorescence Up-Conversion Spectroscopy of Adenine and Adenosine: Experimental Evidence for the πσ* State?" Chem. Phys. 313, 199 - 212 (2005).
Kerr-gated broadband femtosecond fluorescence spectroscopy is a powerful alternative to femtosecond fluoresence up-conversion. The fluorescence of the molecules in the sample solution in a 1 mm cuvette is excited by a femtosecond pump pulse and detected by a CCD detector after passing through two crossed linear polarizers and a grating spectrograph. The Kerr gate is positioned between the polarizers. Under normal conditions, the emission is nulled. However, a short near-IR gate pulse polarized at 45o with respect to the first polarizer creates an optical anisotropy in the Kerr medium, leading to a rotation of the fluorescence polarization and thereby a partial transmission through the second polarizer. The Kerr switch is open, when the gate pulse is on, and shut, when the gate pulse is off. The advantage compared the fluorescence up-conversion technique is that the entire fluorescence spectrum is detected at each pump-probe delay step. Using CCl4 as Kerr medium, we routinely reach a time resolution of ~120 fs.
- U. C. Stange, M. C. Stuhldreier, M. Malicki, C. Schüler, J. Kleber, T. Muskat, F. Temps, Manuscript in preparation.
Transient electronic absorption
Femtosecond Transient Electronic Absorption Spectroscopy (fs-TEAS) is the most versatile tool for the investigation of ultrafast processes and the main work horse in our group. The molecules in the sample solution contained in a thin (0.1 - 1 mm) flow cell or in a wire-guided free-flowing laminar liquid film are photo-excited by a 20 - 25 fs UV or VIS laser pulse from a wavelength-tunable non-collinear optical parametric amplifier (NOPA) equipped with a prism pulse compressor and an optional frequency-doubling stage. The optical response of the sample is then interrogated as function of pump-probe delay time by a broadband supercontinuum pulse in the UV-VIS or near-IR spectral region generated in sapphire or CaF2.
Schematic experimental setup for femtosecond broadband transient electronic absorption spectroscopy.
Our current setup has an additional beam path for single-color detection in the UV. (c) F. Temps
Thanks to a fast frame transfer (FFT) readout CCD camera, single-shot detection electronics at 1 kHz, and a pulse-to-pulse discriminator, we reach a broadband detection sensitivity of ΔOD ≤ 2 × 10-6, at a time resolution of Δt ~ 25 - 35 fs. An additional single-color probe beam (not shown in the figure below) allows us to follow the dynamics at deep-UV wavelengths with a detection sensitivity of ΔOD ≤ 5 × 10-6.
- K. Röttger, S. Wang, F. Renth, J. Bahrenburg, F. Temps, "A Femtosecond Pump-Probe Spectrometer for Dynamics in Transmissive Polymer Films", Appl. Phys. B 118, 185 - 193 (2015). DOI: 10.1007/s00340-014-5967-y
- K. Röttger, R. Siewertsen, F. Temps, "Ultrafast Electronic Deactivation Dynamics of the Rare Nucleobase Hypoxanthine", Chem. Phys. Lett. 536, 140 - 146 (2012). DOI: 10.1016/j.cplett.2012.03.106
- F. Renth, M. Foca, A. Petter, F. Temps, "Ultrafast Transient Absorption Spectroscopy of the Photo-Induced Z - E Isomerization of a Photochromic Furylfulgide," Chem. Phys. Lett. 428, 62 - 67 (2006).
Transient vibrational absorption
Our latest development, femtosecond Transient Vibrational Absorption Spectroscopy (fs-TVAS), complements our existing Transient Electronic Absorption Spectrometer by adding chemically specific detection in the infrared spectral region at wavenumbers from 800 - 4000 cm-1.
Experimental setup for femtosecond transient vibrational absorption spectroscopy. (c) H. Böhnke, F. Temps
The measurement of vibrational bands of observable intermediates and products in the IR with a time resolution < 100 fs allows us to identify the species based on comparison with their (calculated) vibrational spectra. Current applications include investigations of H-transfer switches and the dynamics of DNA building blocks. CaF2.
Chemiluminescence (CL), laser induced fluorescemce (LIF) and particle imaging velocimetry (PIV) are tools which we use to look into fine details of combustion processes, in flames and in a one-cylinder test engine.
- A. Thrun, F. Temps, J. Bauer, "Investigation of Turbulent Combustion and Flame Extinction in a One-Cylinder Internal Combustion Engine", VDI-Nachrichten 2267, 723 - 728 (2015).
Setup for Laser Induced Fluorescence Excitation (LIFE) and Dispersed Fluorescence (DF) spectroscopy
of isolated molecules and free radicals in a free jet expansion (Ph.D. Thesis H. Nicken). (c) CAU Kiel
- H. Nicken, F. Temps, E. Jalviste, "Dispersed Fluorescence Spectra of 1H- and 1D-Indazole", Z. Phys. Chem. 225, 1457 - 1469 (2011). DOI: 10.1524/zpch.2011.0197.
Stimulated emission pumping
- J. Wei, A. Tröllsch, C. M. Tesch, F. Temps, "Rotational State Dependent Mixings between Resonance States of Vibrationally Highly Excited DCO (X 2A')," J. Chem. Phys. 120, 10530 - 10542 (2004).
- F. Renth, A. Tröllsch, F. Temps, "Intramolecular Vibrational Energy Redistribution, Mode Specificity, and Non-Exponential Unimolecular Decay of Vibrationally Highly Excited States of DCO (X 2A')", J. Chem. Phys. 118, 659 - 668 (2003).
- F. Temps, A. Troellsch, "Analysis of Highly Excited Vibrational Bound and Resonance States of DCO (X 2A) using an Effective Polyad Model Hamiltonian", Z. Phys. Chem. 215, 207 - 232 (2001).
- C. Stöck, X. Li, H.-M. Keller, R. Schinke, F. Temps, "Unimolecular Dissociation Dynamics of Highly Vibrationally Excited DCO (X 2A'): I. Investigation of Dissociative Resonance States by Stimulated Emission Pumping Spectroscopy", J. Chem. Phys. 106, 5333 - 5358 (1997).
- S. Dertinger, A. Geers, J. Kappert, F. Temps, J. W. Wiebrecht, "Rotation-Vibration State Resolved Unimolecular Dynamics of Highly Vibrationally Excited CH3O (X 2E): III. State Specific Dissociation Rates from Spectroscopic Line Profiles and Time Resolved Measurements", Faraday Discuss. Roy. Soc. 102, 31 - 52 (1995).
Experimental setup for Resonance Enhanced Multi-Photon Ionization (REMPI) spectroscopy of isolated
molecules and free radicals in a free jet expansion (Ph.D. Thesis H. Nicken). (c) CAU Kiel
- E. Jalviste, S. Dziarzhytski, F. Temps, "Electronic Spectra of Hydrogen-Bonded Self and Water Complexes of Indazole", Z. Phys. Chem. 222, 695 - 714 (2008). DOI: 10.1524/zpch.2008.5347
Velocity-map photofragment imaging
- F. Renth, J. Riedel, F. Temps, "Inversion of Velocity Map Ion Images using Iterative Regularization and Cross Validation," Rev. Sci. Instrum. 77, 033103 (2006).
- J. Riedel, S. Dziarzhytski, A. Kucmann, F. Renth, F. Temps, "Velocity Map Imaging of H Atoms from the Dissociation of HCO (A 2A”) using Doppler-Free Multi-Photon Ionization"; Chem. Phys. Lett. 414, 473 - 478 (2005).
- J. Wei, J. Riedel, A. Kuczmann, F. Renth, F. Temps, "Photodissociation of Pyrrole: Evidence for Mode Specific Dynamics from Conical Intersections," Faraday Discussion 127 - Non-Adiabatic Effects in Chemical Dynamics 127, 267 - 282 (2004).
- J. Wei, A. Kucmann, J. Riedel, F. Renth, F. Temps, "Photofragment Velocity Map Imaging of H Atom Elimination in the First Excited State of Pyrrole", Phys. Chem. Chem. Phys. 5, 315 - 320 (2003).
Cavity ringdown spectroscopy
Cavity-ringdown spectroscopy (CRDS) is an extraordinarily sensitive and enormously valuable tool for detecting trace concentrations of non-fluorescent molecules in the laboratory and in the environment.
After his call to the new Chair of Marine Surface Chemistry and Physical Chemistry, the CRDS projects at CAU Kiel are continued at a very high level in the group of Prof. Gernot Friedrichs.
- G. Friedrichs, J. Bock, F. Temps, P. Fietzek, A. Körtzinger, D. W. R. Wallace, "Towards Continuous Monitoring of Seawater 13CO2/12CO2 Isotope Ratio and pCO2: Performance of Cavity Ringdown Spectroscopy and Gas Matrix Effects", Limnol. Oceanogr. Methods 8, 539 - 551 (2010). DOI: 10.4319/lom.2010.8.539
- G. Friedrichs, M. Fikri, Y. Gua, F. Temps, "Time-Resolved Cavity Ringdown Measurements and Kinetic Modeling of the Pressure Dependence of the Recombination Reactions of SiH2 with the Alkenes C2H4, C3H6, and t-C4H8," J. Phys. Chem. A 112, 5636 - 5646 (2008). DOI: 10.1021/jp8012128
- G. Friedrichs, M. Colberg, M. Fikri, Z. Huang, J. Neumann, F. Temps, "Validation of an Extended Simultaneous Kinetics and Ringdown Model by Measurements of the Reaction NH2 + NO", J. Phys. Chem. A 109, 4785 - 4795 (2005).
- Y. Guo, M. Fikri, G. Friedrichs, F. Temps, "An Extended Simultaneous Kinetics and Ringdown Model: Determination of the Rate Constant for the Reaction SiH2 + O2," Phys. Chem. Chem. Phys. 5, 4622 - 4630 (2003).
Time-resolved MS for gas kinetics
- G. Friedrichs, E. Goos, J. Gripp, H. Nicken, J.-B. Schönborn, H. Vogel, F. Temps, "The Products of the Reactions of o-Benzyne with Ethene, Propene, and Acetylene: A Combined Mass Spectrometric and Quantum Chemical Study", Z. Phys. Chem. 223, 387 - 407 (2009). DOI: 10.1524/zpch.2009.6042
- W. Ludwig, B. Brandt, G. Friedrichs, F. Temps, "Kinetics of the Reaction C2H5 + HO2 by Time-Resolved Mass Spectrometry", J. Phys. Chem. A 110, 3330 - 3337 (2006).
- T. Köcher, C. Kerst, G. Friedrichs, F. Temps, "The Gas Phase Oxidation of Silyl Radicals by Molecular Oxygen: Kinetics and Mechanisms", in: Silicon Chemistry - From Small Molecules to Extended Systems, eds. P. Jutzi and U. Schubert, Wiley-VCH, pp. 44 - 57 (2003).
- G. Eshchenko, T. Köcher, C. Kerst, F. Temps, "Formation of HCNO and HCN in the 193 nm Photolysis of H2CCO in the Presence of NO", Chem. Phys. Lett. 356, 181 - 187 (2002).
- M. Fikri, St. Meyer, J. Roggenbuck, F. Temps, "An Experimental and Theoretical Study of the Product Distribution of the Reaction CH2 (X 3B1) + NO," Faraday Discuss. Roy. Soc. 119, 223 - 242 (2001).
- U. Eickhoff, F. Temps, "An FTIR Study of the Products of the Reaction between HCCO and NO", Phys. Chem. Chem. Phys. 1, 243 - 251 (1999).
FT microwave spectroscopy
Two home-built MB-FTMW spectrometers (one with double resonance capability) are fully operational for research and for routine use. Besides, they are also used for training in advanced lab courses for Master students.
Molecular Beam - Fourier-Transform Microwave Spectrometer. (c) CAU Kiel
- C. Rensing, H. Mäder, F. Temps, "Rotational Spectrum, Structure and Internal Dynamics of the Pyrrole ∙ Ammonia Complex", J. Mol. Spectrosc. 251, 224 - 228 (2008). DOI: 10.1016/j.jms.2008.02.024
- T. Pancur, K. Brendel, N. Hansen, H. Mäder, V. Markov, F. Temps, "Microwave Spectra of the 35Cl and 37Cl Isotomopers of Dichloromethylene: Nuclear Quadrupole, Spin-Rotation and Nuclear Shielding Constants from the Hyperfine Structures of Rotational Lines," J. Mol. Spectrosc. 232, 375 - 379 (2005).
- N. Hansen, H. Mäder, F. Temps, "Rotational Transitions of the C2H3O Radical Detected by Pulsed Laser Photolysis - Molecular Beam - Fourier Transform Microwave Spectroscopy", J. Mol. Spectrosc. 209, 278 - 279 (2001).
- N. Hansen, H. Mäder, F. Temps, "The Rotational Spectrum of CCl2 (X 1A1) Observed by Molecular Beam - Fourier Transform Microwave Spectroscopy", Phys. Chem. Chem. Phys. 3, 50 - 55 (2001).
- N. Hansen, H. Mäder, F. Temps, "Nuclear Spin-Rotation Interaction in CF2 (X 1A1) Observed by Fourier-Transform Microwave Spectroscopy", Chem. Phys. Lett. 327, 97 - 103 (2000).
Chemistry lab and infrastructure
We seek to investigate the most suitable and ideal sample molecules to solve a specific scientific problem, regardless of whether they are commercially available or not. Many of our samples need to be synthesized and purified, this work may sometimes take a fair amount of dedication and time. Other samples require special preparations for the subsequent dynamics measurements. Our Chemistry Laboratory designed towards these ends features all standard equipment for chemical syntheses, including stations for synthesis under inert gas atmospheres, Schlenk stations, vacuum distillation, rotary evaporators, flash chromatography, etc. Samples which are sensitive to atmospheric humidity are routinely handled in a dry box.
Desktop spectrometers for routine measurements:
- Shimadzu UV-2401UV-VIS desktop spectrometer,
- Horiba Jobin Yvon Fluoromax 4 desktop fluorescence spectrometer,
- Picoquant FluoTime 200 TCSPC fluorescence spectrometer,
- Bruker IFS 66v FTIR spectrometer for liquid phase and gas phase samples.
- In-house technical support is provided by the Mechanics Workshop, well equipped with modern computerized machinery, and by the Electronics Workshop of the Institute of Physical Chemistry.
- Furthermore, the Chemistry Department runs several NMR spectrometers and X-ray diffraction spectrometers for analysis of crystal structure.
- A transmission electron microscopy (TEM) facility for analysis of nanoparticles is operated by the Department of Materials Science.