Research
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Our research activity is in the general areas of molecular physics and spectroscopy and can be broadly divided into three main areas: (i) high-resolution atomic and molecular spectroscopy (ii) cold molecules and cold chemistry, and (iii) molecular photoionization. Rydberg states are a central theme of most of our investigations. A characteristic feature of our scientific approach is that we develop the instrumentation, i.e., light sources, spectrometers, beam-deceleration devices, etc. used in our research in house, relying on a close collaboration with the mechanical and electronics workshops of the Physical Chemistry Laboratory.
In the first area, our group investigates the structure and dynamics of atoms and molecules using laser spectroscopy in the vacuum ultraviolet (VUV), UV, visible, submillimeter, millimeter and microwave ranges of the electromagnetic spectrum. Our goal is to simultaneously achieve high spectral resolution, broad frequency coverage and accurate frequency calibration. We continuously develop our laser sources, extend their tunable ranges, and calibrate their frequencies using frequency combs, which we reference to secondary (GPS rubidium) and recently also primary (Caesium fountain clock signal from the Swiss metrology institute METAS in Bern) frequency standards. At present, we have tunable coherent radiation sources covering the ranges from 1 mm to 60 nm and from 100 GHz to 20 THz. A special focus are precision measurements in few-electron atoms (H, He) and molecules (H2+, H2, He2, He2+) and the comparison of experimental energy intervals determined in these systems with the results obtained by ab initio quantum calculations including relativistic and quantum-electrodynamics corrections. Another area of interest are electronically excited states and the study of nonadiabatic dynamics in small polyatomic molecules (Renner-Teller effect, Jahn-Teller effect and rovibronic interactions).
In the second area, we contribute to the development of new methods of controlling the translational motion of atoms and molecules in the gas phase and of generating dense cold molecular samples starting with supersonic molecular beams. We made important contributions to the development of multistage Zeeman deceleration and Rydberg-Stark deceleration. We exploit our cold-atom and cold-molecule sources to study chemical reactions at very low temperature and in metrology applications. A special focus is the study of ion-molecule reactions of astrophysical interest in the range between 0 and 50 K. Currently, the main focus is on studies of the reactions of He+ and H2+ with neutral molecules such as N2, O2, NO, CO, NH3, CH4, and CH3F.
In the third area, we investigate the process of photoionization in atoms and molecules using high-resolution photoionization mass spectrometry and photoelectron spectroscopy. We study how photoionization affects the vibrational, rotational motion of molecules, and even the role of the fine and hyperfine structures. Of particular interest for our studies are the regions close to the ionization thresholds, where the autoionization dynamics of high Rydberg states can be used to obtain a global understanding of molecular photoionization and to measure the energy level structure of molecular cations with high precision. Recently, we have extended these studies to (i) the photoionization of molecular cations such Mg+, Mg2+, MgAr+, MgKr+, which offers a route to study dications (e.g., Mg2+2, MgAr+2, MgKr+2 by high-resolution spectroscopy and (ii) the excitation of ion-pair states and heavy-Rydberg systems (H+-SH-, D+-SD-).
The following review articles, written to accompany our research, provide information on several of the topics listed above:
[1] "Molecules in high Rydberg states"
F. Merkt, Ann. Rev. Phys. Chem. 48, 675 - 709 (1997),
doi: external page 10.1146/annurev.physchem.48.1.675
[2] "Millimeter wave spectroscopy of high Rydberg states"
F. Merkt and A. Osterwalder, Int. Rev. Phys. Chem. 21, 385 - 403 (2002),
doi: external page 10.1080/01442350210151641
[3] "High-Resolution Spectroscopy of the Metastable Helium Molecule and its Cation".
Jansen P., Habilitation (2020).
doi: external page 10.3929/ethz-b-000437390
[4] "Deceleration of supersonic beams using inhomogeneous electric and magnetic fields"
S. D. Hogan, M. Motsch, and F. Merkt, Phys. Chem. Chem. Phys. 13, 18705 - 18723 (2011),
doi: external page 10.1039/C1CP21733Jcall_made
[5] "High-resolution photoelectron spectroscopy"
F. Merkt, S. Willitsch, and U. Hollenstein, in: "Handbook of High-Resolution Spectroscopy", Vol. 3, 1617 - 1654, Eds. M. Quack and F. Merkt, Wiley & Sons, U.K. (2011),
doi: external page 10.1002/9780470749593.hrs071call_made
[6] "Fundamentals of electronic spectroscopy"
H. J.Wörner and F. Merkt, in: "Handbook of High-Resolution Spectroscopy", Vol. 1, 175 - 262, Eds. M. Quack and F. Merkt, Wiley & Sons, U.K. (2011),
doi: external page 10.1002/9780470749593.hrs069call_made
[7] "Molecular quantum mechanics and molecular spectra, molecular symmetry, and interaction of matter with radiation"
F. Merkt and M. Quack, in: "Handbook of High-Resolution Spectroscopy", Vol. 1, 1 - 55, Eds. M. Quack and F. Merkt, Wiley & Sons, U.K. (2011),
doi: external page 10.1002/9780470749593.hrs001call_made
[8] "Photoionization dynamics of excited Ne, Ar, Kr, and Xe atoms near threshold"
V. L. Sukhorukov, I. D. Petrov, M. Schäfer, F. Merkt, M.-W. Ruf, and H. Hotop, J. Phys. B: At. Mol. Opt. Phys. 45, 092001:1-43 (2012),
doi: external page 10.1088/0953-4075/45/9/092001call_made
[9] «Molecular-physics aspects of cold chemistry»
F. Merkt
in: «Current Trends in Atomic Physics», Les Houches 2016 Lecture Notes, Oxford University Press, Oxford, 82-141 (2019)
doi: external page 10.1093/oso/9780198837190.003.0003
For a more detailed description of our research topics, visit the Research page or learn more about our research by reading one of our Publications.