Werner Fuß
Max Planck Society
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Featured researches published by Werner Fuß.
Journal of Chemical Physics | 2000
Werner Fuß; Wolfram E. Schmid; Sergei A. Trushin
The concerted photochemical ring opening of 1,3-cyclohexadiene was investigated in the gas phase by low-intensity pumping at 267 nm and subsequent probing by high-intensity photoionization at 800 nm and mass-selective detection of the ion yields. We found five different time constants which can be assigned to traveling times along consecutive parts of the potential energy surfaces. The molecule is first accelerated in the spectroscopic state 1B along Franck–Condon active coordinates, then alters direction before changing over to the dark state 2A. All constants including that for leaving the 2A surface are below 100 fs. These times are shorter than appropriate vibrational periods. Such a maximum speed is evidence that the pathway is continuous leading from surface to surface via real crossings (conical intersections) and that the molecule is accelerated right into the outlet of the 2A/1A funnel. On the ground state it arrives as a compact wave packet, indicating a certain degree of coherence. The experime...
Chemical Physics | 1998
Werner Fuß; Stefan Lochbrunner; Astrid M. Müller; T. Schikarski; Wolfram E. Schmid; Sergei A. Trushin
Abstract The dynamics of molecules, attention to which is being stimulated by modern ultrafast spectroscopy, as well as progress in quantum chemistry are giving new impetus to the approach which follows the detailed pathway of the molecules along the potential energy surfaces from the excited to the ground state. Local properties such as slopes, saddle points, barriers and funnels with conical intersections as exits are taken into account. We show the fruitfulness of this approach by means of new and published experimental results on photochemical pericyclic reactions. The experimental data support the importance of conical intersections and, in some cases, yield a very detailed picture of the dynamics on the potential energy surfaces. We emphasize the relation of the pericyclic potential surfaces to those of cis–trans isomerization and show that, in this case, the geometries of the conical intersections are interrelated and can be intuitively understood. The conical intersections of stilbene and polyenes can be deduced from the prototype of ethylene, and their geometries are supported by photochemical evidence.
Chemical Physics | 2000
Werner Fuß; Yehuda Haas; Shmuel Zilberg
Abstract We suggest for linear conjugated polyenes a twin state model which represents the ground state (S 0 ) and first excited state (S 1 ) as a superposition of mainly two mesomeric structures, the fully spin-paired one and a diradical. This model rationalizes why the bond-length alternation, which is pronounced in S 0 , more or less disappears in S 1 and why the bond-alternation vibration (highest frequency CC stretch) is raised in S 1 and depressed in S 0 . The similarity to the Peierls effect and Kohn anomaly in one-dimensional metals is emphasized. Moreover, the conical intersection between S 2 and S 1 is qualitatively predicted, and invoking in addition, some spectroscopic and other observations and the phase-change rule, that between S 1 and S 0 can also be predicted. Compared with the consideration of densities of states and matrix elements, these intersections more satisfactorily explain the S 2 /S 1 and S 1 /S 0 internal conversions and their dependence on chain length, substituents, solvent and temperature and is furthermore consistent with photochemistry. This also includes an exponential gap rule for the internal-conversion rates, which is derived from a proposed dependence of the energy at the intersection on the S 1 –S 0 energy gap.
Photochemistry and Photobiology | 2002
Diego Sampedro Ruiz; Alessandro Cembran; Marco Garavelli; Massimo Olivucci; Werner Fuß
Abstract High-level ab initio calculations show that the singlet photochemical cis–trans isomerization of organic molecules under isolated conditions can occur according to two distinct mechanisms. These mechanisms are characterized by the different structures of the conical intersection funnels controlling photoproduct formation. In nonpolar (e.g. hydrocarbon) polyenes the lowest-lying funnel corresponds to a (CH)3 kink with both double and adjacent single bonds twisted, which may initiate hula-twist (HT) isomerization. On the other hand, in polar conjugated systems such as protonated Schiff bases (PSB) the funnel shows a structure with just one twisted double bond. The ground-state relaxation paths departing from the funnels indicate that the HT motion may take place in nonpolar conjugated systems but also that the single-bond twist may be turned back, whereas in free conjugated polar molecules such as PSB a one-bond flip mechanism dominates from the beginning. The available experimental evidence either supports these predictions or is at least consistent with them.
Journal of Chemical Physics | 1997
Sergei A. Trushin; Werner Fuß; T. Schikarski; Wolfram E. Schmid; K. L. Kompa
We found that hydrogen ion formation due to multielectron dissociative ionization by an intense-laser field is much less efficient with 1,3-cyclohexadiene than with its isomer 1,3Z,5-hexatriene (Z-HT). Moreover by suppressing the ionization barrier an intense-laser field ejects electrons most efficiently from molecular states of low ionization potential. After pumping 1,3-cyclohexadiene at 267 nm to its 1B2 state we probe the system by intense-laser field ionization with delayed 800 nm pulses. Monitoring of the parent ion C6H8+, of the main fragment C6H7+ and of H+ allows us to follow the motion from the 1B2 surface to the dark 2A1 state and from there towards the 2A1/1A1 conical intersection to the ground-state surface of the product. The measured 1B2 and 2A1 lifetimes are 43±3 and 77±7 fs, respectively, and the primary photoproduct cZc-HT is produced within 200 fs.
Chemical Physics Letters | 2002
Lars Windhorn; Thomas Witte; Jake S. Yeston; D. Proch; Marcus Motzkus; Karl-Ludwig Kompa; Werner Fuß
Abstract By focusing a MIR femtosecond laser in a cell containing gas-phase metal carbonyls, the resonant infrared multiphoton dissociation of molecules was observed. Cr(CO)6,Mo(CO)6,W(CO)6, and Fe(CO)5 could easily be dissociated, which requires an excitation to at least v=7 or 8 of the CO stretch vibration. After irradiation with ∼150 fs pulses at 5 μm the metal carbonyl practically disappears in favor of free CO, as detected by the IR spectrum. By comparing the power dependence of the total conversion with a model, we can infer that only few vibrational degrees of freedom are involved in the excitation process.
Chemical Physics | 2000
Sergei A. Trushin; Werner Fuß; Wolfram E. Schmid
Abstract By time-resolved nonresonant (800 nm) multiphoton ionization we found five consecutive processes and pronounced coherent oscillations after excitation of M(CO) 6 , M=Cr, Mo and W at 267 nm in the gas phase. We suggest that the first two steps correspond to relaxation along a Jahn–Teller (JT) active coordinate and internal conversion between metal-to-ligand charge-transfer states via a JT induced conical intersection, whereas in the third step the molecules change over to a repulsive ligand-field surface and dissociate. The primary product is M(CO) 5 in its S 1 state which can again relax in an ultrashort time through a JT induced conical intersection to S 0 ; the JT active coordinate (relaxation pathway) corresponds to pseudorotation. The total time to reach S 0 takes 110, 165 and 195 fs for the three carbonyls (calculated from the measured first four time constants). After arrival at S 0 , M(CO) 5 oscillates coherently along a pseudorotation coordinate. In S 0 , M(CO) 5 eliminates a second CO in about 1 ps owing to its vibrational excess energy, a step which is suppressed in solution by cooling. All processes take place in the singlet manifold of states.
Optics Letters | 2008
Kyriaki Kosma; Sergei A. Trushin; Wolfram E. Schmid; Werner Fuß
We demonstrate that in a short Ar cell, generation of the fifth harmonic from 12 fs pulses at 810 nm directly results in ultrashort vacuum UV pulses at 162 nm. They have a spectral width of approximately 5 nm and a duration of 11+/-1 fs (1.4 times the transform limit), as measured by cross correlation with the fundamental pulses. Their energy (estimated to 4 nJ) turned out to be sufficient for use as a pump in time-resolved experiments.
Journal of Chemical Physics | 2003
Lars Windhorn; Jake S. Yeston; Thomas Witte; Werner Fuß; Marcus Motzkus; D. Proch; Karl-Ludwig Kompa; C. Bradley Moore
Gaseous diazomethane (CH2N2) has been irradiated with femtosecond laser pulses tuned to the CNN asymmetric stretch at 2100 cm−1 in the mid-infrared. Laser-induced fluorescence detection of 1CH2 [537 nm, b1B1(0 16 0)←a1A1(0 0 0)] confirms infrared (IR) multiphoton-induced scission of the C–N bond on two distinct time scales, 480±70 fs and 36±8 ps. The longer time scale is consistent with a statistical dissociation process; the shorter one is indicative of directed dissociation, which occurs more rapidly than statistical intramolecular vibrational energy redistribution because of direct coupling of the vibrational energy from the IR-excitation mode into the reaction coordinate. Anisotropy measurements demonstrate that the CH2 group bends significantly out of the molecular plane prior to the dissociation.
Optics Letters | 2007
Sergei A. Trushin; Kyriaki Kosma; Werner Fuß; Wolfram E. Schmid
Focusing 12 fs pulses of 800 nm with moderate energy (0.35 mJ) into atmospheric-pressure argon (Ar) gives rise to filamentation (self-focusing) and a supercontinuum with a very broad pedestal, extending to 250 nm. According to the present understanding, the short wavelengths are produced by self-phase modulation in the self-steepened trailing edge of the pulse. Pulses in this spectral range might thus be intrinsically short. Indeed we demonstrate this by extracting the light near the end of the filament, terminating self-focusing by a pressure gradient at a pinhole, beyond which the Ar is pumped away. We obtain pulses of 9.7 fs in the region of 290 nm without the necessity of compression.