Researchers at MBI fulfill a long-cherished dream and study molecular conversion on a time scale of a few femtoseconds

The observation of crucial first femtoseconds in a photochemical reaction requires experimental techniques that are not found in the typical arsenal of femtosecond chemistry. But such fast dynamics can now be studied with the tools of attosecond research. In the study by Galbraith et al., Published this week in Nature Communications, researchers at MBI have studied one of the fastest internal conversion processes in a molecule at all.

When Horst Köppel published his first scientific article on the ionic benzene molecule in 1987, Martin Galbraith was just born. Köppel, professor in Heidelberg, had found the perfect touchstone for the forthcoming development of a new theoretical method, the so-called time-resolved multiple configuration Hartree calculation, for which he and his colleagues became famous during the following decades. The omnipresent benzene molecule in our environment, whose backbone consists of a ring of six carbon atoms, turned out to be the perfect compromise between complexity and chemical relevance. Therefore, the theoretical specialists from Heidelberg have studied this molecule more and more closely and over the years have written more than 30 highly cited publications, while they have developed their technique to a cutting-edge tool of theoretical chemistry, which is now used by scientists around the world.

But one crucial thing was not yet achievable: the confirmation of the theoretical results by a time-resolved experiment. The predicted dynamics were just too fast, on a time scale of about 10 femtoseconds. This extremely small time interval is obtained by dividing a second by 1014, that is, by a 14-digit number.

Fig. 1: Schematic overview of the lowest eight component states of the benzene ion, represented as potential energy V in eV as a function of a dimensionless effective nuclear coordinate Qeff. The purple arrows mark the ionization by the pump pulse, the orange arrows the excitation by the interrogation pulse. The dashed black line indicates the energy necessary to obtain the fragment C4H3+. The dot-dashed green lines are a schematic representation of the time evolution of an ion generated in the E state, which passes through a series of internal conversion processes through the marked conical overlapping first to the D state and then to the B state.

When Horst Köppel published his first scientific article on the ionic benzene molecule in 1987, Martin Galbraith was just born. Köppel, professor in Heidelberg, had found the perfect touchstone for the forthcoming development of a new theoretical method, the so-called time-resolved multiple-configuration Hartree calculation, for which he and his colleagues became famous during the following decades. The omnipresent benzene molecule in our environment, whose backbone consists of a ring of six carbon atoms, turns out to be the perfect compromise between complexity and chemical relevance. Therefore, the theoretical specialists from Heidelberg have studied this technique, and they have developed their technique to a cutting-edge tool of theoretical chemistry, which is now used by scientists around the world.

But one thing is not achievable: the confirmation of the results by a time-resolved experiment. The predicted dynamics were just too fast, on a time scale of about 10 femtoseconds. This is a very small time interval by 1014, that is, by a 14-digit number.

Fig. 2: Experimentally measured C4H3+ fragment signal as a function of time delay between pump and interrogation pulse (red dots). The black line is a bi-exponential fit to the data, the dashed lines indicate the contributions of the two time scales resulting from the traversals of the sequential conical intersections. The small picture at the top right shows a measurement over a long time delay.

The present scientific study results from a collaboration of the MBI researchers with the theory groups of Professor Horst Köppel and Alexander Kuleff at the University of Heidelberg. "I think it's great that after so many years that our calculations on benzene ion were just a standard for theorists, a detailed comparison of theory and experiment is now possible and can confirm our calculations," says Horst Köppel. The published work includes recent, more detailed calculations, which Simona Scheit were executed by the Heidelberg group, and shows a very good agreement between experiment and theory.

Molecular dynamics at conical overlaps plays a central role in many key fields of modern chemistry. Often the first femtoseconds are of crucial importance, which until now could not be understood experimentally. That's why Dr. Jochen Mikosch confident about the future of the experimental technique that has now been developed, concludes: "By observing one of the fastest internal conversion processes in a molecule, we have opened a new field that gives us ways to control electronic dynamics in complex molecules. ".

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Publications since 2025

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A1-P-2025.01
Melting, bubblelike expansion, and explosion of superheated plasmonic nanoparticles

S. Dold, T. Reichenbach, A. Colombo, J. Jordan, I. Barke, P. Behrens, N. Bernhardt, J. Correa, S. Düsterer, B. Erk, T. Fennel, L. Hecht, A. Heilrath, R. Irsig, N. Iwe, P. Kolb, B. Kruse, B. Langbehn, B. Manschwetus, P. Marienhagen, F. Martinez, K.-H. Meiwes-Broer, K. Oldenburg, C. Passow, C. Peltz, M. Sauppe, F. Seel, R. M. P. Tanyag, R. Treusch, A. Ulmer, S. Walz, M. Moseler, T. Möller, D. Rupp, B. v. Issendorff

Physical review letters 134 (2025) 136101/1-7

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A3-P-2025.01
Second-harmonic generation in OP-GaAs0.75P0.25 heteroepitaxially grown from the vapor phase

L. Wang, S. R. Vangala, S. Popien, M. Beutler, J. M. Mann, V. L. Tassev, E. Büttner, V. Petrov

CrystEngComm 27 (2025) 1373-1376

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A3-P-2025.02
Diode-pumped Kerr-lens mode-locked Yb:MgWO4 laser

H.-Y. Nie, Z.-L. Lin, P. Loiko, H.-J. Zeng, L. Zhang, Z. Lin, G. Z. Elabedine, X. Mateos, V. Petrov, G. Zhang, W. Chen

Optics Letters 50 (2025) 1049-1052

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A3-P-2025.03
Growth, anisotropy, and spectroscopy of Tm3+ and Yb3+ doped MgWO4 crystals

G. Z. Elabedine, R. M. Solé, S. Slimi, M. Aguiló, F. Díaz, W. Chen, V. Petrov, X. Mateos

CrystEngComm 27 (2025) 1619-1631

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A3-P-2025.04
Growth, structure, spectroscopic, and laser properties of Ho-doped yttrium gallium garnet crystal

S. Slimi, H. Yu, H. Zhang, C. Kränkel, P. Loiko, R. M. Solé, M. Aguiló, F. Díaz, W. Chen, U. Griebner, V. Petrov, X. Mateos

Optics Express 33 (2025) 2529-2541

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A3-P-2025.05
Growth, spectroscopy and laser operation of disordered Tm,Ho:NaGd (MoO4)2 crystal

G. Z. Elabedine, Z. Pan, P. Loiko, H. Chu, D. Li, K. Eremeev, K. Subbotin, S. Pavlov, P. Camy, A. Braud, S. Slimi, R. M. Solé, M. Aguiló, F. Díaz, W. Chen, U. Griebner, V. Petrov, X. Mateos

Journal of Alloys and Compounds 1020 (2025) 179211/1-12

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A3-P-2025.06
Kerr-lens mode-locked, diode-pumped Yb,Gd:YAP laser generating 23 fs pulses

H.-Y. Nie, P. Zhang, P. Loiko, Z.-L. Lin, H.-J. Zeng, G. Zhang, Z. Li, X. Mateos, H.-C. Liang, V. Petrov, Z. Chen, W. Chen

Optics Express 33 (2025) 11793-11799

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A3-P-2025.07
Nanoindentation and laser-induced optical damage tests of CdSe nonlinear crystals

G. Exner, A. Carpenter, K. Cissner, A. Hildenbrand-Dhollande, S. Schmitt, A. Grigorov, M. Piotrowski, S. Guha, V. Petrov

Journal of the Optical Society of America B 42 (2025) A10-A14

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A3-P-2025.08
Phase-matching properties of AgGa(Se1-xTex)2 for SHG of a CO2 laser

K. Kato, V. Petrov, K. Miyata

Proceedings of SPIE 13347 (2025) 133470S/1-4

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A3-P-2025.09
Phase-matching properties of ZnSiAs2 in the mid-IR

T. Okamoto, N. Umemura, K. Kato, V. Petrov

Proceedings of SPIE 13347 (2025) 133470C/1-5

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A3-P-2025.10
Direct generation of 3.5 optical-cycle pulses from a rare-earth laser

N. Zhang, Y. Wang, H. Ding, F. Liang, Y. Zhao, J. Xu, H. Yu, H. Zhang, V. Petrov

Optics Letters 50 (2025) 3150-3153

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A3-P-2025.11
Power scaling of a non-resonant optical parametric oscillator based on periodically poled LiNbO3 with spectral narrowing

S. Das, T. Temel, G. Spindler, A. Schirrmacher, I. B. Divliansky, R. T. Murray, M. Piotrowski, L. Wang, W. Chen, O. Mhibik, V. Petrov

Optics Express 33 (2025) 5662-5669

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A3-P-2025.12
Sub-40-fs diode-pumped ytterbium-doped mixed rare-earth calcium oxoborate laser

H.-J. Zeng, Z.-L. Lin, H. Lin, P. Loiko, L. Zhang, Z. Lin, H.-C. Liang, X. Mateos, V. Petrov, G. Zhang, W. Chen

Optics Express 33 (2025) 17965-17975

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A3-P-2025.13
Spectroscopy and SESAM mode-locking of a disordered Yb:Gd2SrAl2O7 crystal

H.-J. Zeng, Z.-L. Lin, P. Loiko, F. Yuan, G. Zhang, Z. Lin, X. Mateos, V. Petrov, W. Chen

Optics Express 33 (2025) 15057-15066

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A3-P-2025.14
Watt-level, 1.6 ps χ(2)-lens mode-locking of an in-band pumped Nd:LuVO4 laser

H. Iliev, V. Aleksandrov, V. Petrov, L. S. Petrov, H. Zhang, H. Yu, I. Buchvarov

Optics Express 33 (2025) 17773-17781

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A3-P-2025.15
Refined phase-matching predictions for AgGa1-xInxS2 mixed chalcopyrite crystals

K. Kato, K. Miyata, V. Petrov

Journal of the Optical Society of America B 42 (2025) A6-A9

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A3-P-2025.16
35-fs diode-pumped mode-locked ytterbium-doped multi-component alkaline-earth fluoride laser

Z. Zhang, Z.-Q. Li, P. Loiko, H.-J. Zeng, G. Zhang, Z.-L. Lin, S. Normani, A. Braud, F. Ma, X. Mateos, H.-C. Liang, V. Petrov, D. Jiang, L. Su, W. Chen

Optics Letters 50 (2025) 1835-1838

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A3-P-2025.17
Diode-pumped few-optical-cycle laser based on an ytterbium-doped disordered strontium yttrium borate crystal

H. Zeng, Z. Lin, S. Sun, P. Loiko, H. Lin, G. Zhang, Z. Lin, C. Mou, X. Mateos, V. Petrov, W. Chen

Optics Letters 50 (2025) 2203-2206

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A3-P-2025.18
Refined Sellmeier and thermo-optic dispersion formulas for CdGeAs2

K. Kato, K. Miyata, V. Petrov

Journal of the Optical Society of America B 42 (2025) A24-A28

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A3-P-2025.19
Diode-pumped mode-locked Yb:Ca3La2(BO3)4 laser generating 35 fs pulses

H.-J. Zeng, Z.-L. Lin, G. Zhang, Z. Pan, P. Loiko, X. Mateos, V. Petrov, H. Lin, W. Chen

Optics Express 33 (2025) 22988-22996

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