Henning Meyer, Professor of Physics and Chemistry
New laser spectroscopic techniques enable the study of dynamic and kinetic processes relevant to combustion and atmospheric chemistry in unprecedented detail. The high output power combined with the spectral brightness of pulsed lasers allows resonance enhanced multiphoton ionization (REMPI) processes to be used for the sensitive detection of a large variety of molecular products, e.g. CO, HCl, NH3, acetaldehyde or radicals like Cl, ClO, CHn, NH and NO.
My research targets the reaction dynamics of isolated molecules and atoms. We employ molecular beam laser spectroscopy to study the interactions of molecules with light, but also with other atomic and molecular partners. If we consider a free molecule, its fate is typically determined by collisions with other atoms or molecules or a surface. We study these interactions through molecular beam scattering experiments but also through high resolution IR spectroscopy of the associated van der Waals complexes. More recently, we extend the scattering experiments towards molecular beam surface scattering.
Alternatively, the molecule can absorb light exciting it to a higher electronic state. While some molecules might simply relax back to the ground state through photon emission, for other molecules, the excitation might result in photodissociation, i.e. the breaking of chemical bonds potentially followed by the subsequent rearrangements of the constituting atoms.
The experiments rely on efficient quantum state detection through REMPI. In combination with high resolution ion time of flight (TOF) analysis, the 3D velocity distribution of the scattered molecules or the fragments from a photodissociation can be reconstructed. A key feature of the experimental set-up, is the realization of cylindrical symmetry. This is accomplished by aligning the relative velocity in a molecular beam scattering experiment, the direction of linear polarization in a photodissociation experiment or the surface normal in a surface scattering experiment with the direction of the weak electric field used for velocity dispersion of the products ions (after state specific REMPI ionization).
In addition to quantum state specific product detection, laser based methods are applied to the preparation of vibrationally excited molecules using either stimulated Raman pumping or IR absorption. Subsequent scattering or photodissociation experiments allow us to study the influence of vibrational excitation on the reaction dynamics.
Molecular Physics and Theoretical Spectroscopy
H. Meyer, Determination of alignment parameters for symmetric top molecules using non-resonant two-photon absorption, Chem. Phys. Lett. 230, 510-518 (1994).
H. Meyer, Determination of ground state populations and alignment parameters using nonresonant three-photon absorption, J. Chem. Phys. 102, 3110-3122 (1995).
H. Meyer and S.R. Leone, Preparation and probing of alignment in molecular ensembles by saturated coherent pulsed laser excitation, J. Chem. Phys.105, 5858-5871 (1996).
H. Meyer, The Molecular Hamiltonian, Ann. Rev. Phys. Chem. 53, 147-172(2002).
Counter progagating pulsed molecular beam scattering:
H. Meyer, "Counterpropagating Pulsed Molecular Beam Scattering," in 'Atomic & Molecular Beams: The State of the Art 2000', Ed. R.D. Campargue, pp. 497-518, Springer, 2001.
Y. Kim, S. Ansari, B. Zwickel and H. Meyer, High resolution ion time-of-flight analysis for measuring molecular velocity distributions, Rev.of Sc. Instr. 74, 4805-4811(2003).
Y. Kim and H. Meyer, Quantum interference in the REMPI detection of aligned NO, Chem. Phys 301, 283-292(2004).
A.V. Demyanenko, V. Dribinski, H. Reisler, H. Meyer, and C.X.W. Quian, Product quantum-state-dependent anisotropies in photoinitiated unimolecular decomposition, J. Chem. Phys. 111, 7383-7396(1999), https://doi.org/10.1063/1.3598339
B. Wen, and H. Meyer, The near-IR spectrum of the NO-CH4 complex, J. Chem. Phys. 131, 034304(01-11) (2009).
IR and UV Spectroscopy of Van der Waals complexes:
Y. Kim and H. Meyer, "Multiphoton Spectroscopy of NO-Rg (Rg = Rare Gas) Van der Waals Systems," Int. Rev. Phys. Chem. 20, 219 (2001).
M.H. Alexander, P. Soldan, T.G. Wright, Y. Kim, H. Meyer, and P.J. Dagdigian, The NO-Ne complex: II. Investigation of the lower bound states based on new potential energy surfaces, J. Chem. Phys. 114, 5588-5597(2001).
B. Wen, Y. Kim, H. Meyer, J. Klos, and M. H. Alexander, IR-REMPIV double resonance spectroscopy: The near IR spectrum of NO-Ar revisited, J. Phys. Chem. A 112, 9483-9493(2008).
H. Meyer, The A-state Dissociation Continuum of NO-Ar and its Near IR Spectrum, J. Chem. Phys. 136, 204308(01-08)(2012).
J. Klos, S.G. Zhang and H. Meyer, The near-IR Spectrum of NO(X)-Ne detected through excitation into the A-state continuum: A joint theoretical -experimental study, J. Chem. Phys., 144, 114307 (2016).
J. Klos, V. Beutner, S.G. Zhang and H. Meyer, The near-IR Spectrum of NO(X)-He detected through excitation into the A-state continuum: A joint theoretical -experimental study, J. Chem. Phys., 145, 124318(2016).
V. Beutner, L.M. Duffy and H. Meyer, Resonance Enhanced Multi-Photon Ionization Detected mm-Wave Absorption: The 115 GHz Line of CO, J. Phys. Chem. A, 2019, 123, 10, 2153-2162