Search

Your search keyword '"Hamm, Peter"' showing total 58 results
Start Over Author "Hamm, Peter" Journal the journal of chemical physics
58 results on '"Hamm, Peter"'

4. Transient CO desorption from thin Pt films induced by mid-IR pumping

Author

Tek, Gökçen, Hamm, Peter, University of Zurich, and Hamm, Peter

Subjects
10120 Department of Chemistry, Aqueous solution, Materials science, 010304 chemical physics, UFSP13-6 Solar Light to Chemical Energy Conversion, Analytical chemistry, General Physics and Astronomy, Photon energy, 010402 general chemistry, 01 natural sciences, Fluence, 3100 General Physics and Astronomy, 0104 chemical sciences, Wavelength, Adsorption, Desorption, 540 Chemistry, 0103 physical sciences, Vibrational energy relaxation, Physical and Theoretical Chemistry, 1606 Physical and Theoretical Chemistry, Spectroscopy
Abstract

Resonant and off-resonant mid-infrared pump–probe spectroscopy is used to measure the vibrational dynamics of CO adsorbed to thin (0.2 nm, 2 nm, and 10 nm) heterogeneous Pt layers in an aqueous solution. The transient signals observed with resonant pumping are dominated by vibrational relaxation of the CO internal stretch vibration with a lifetime of T1 ∼ 3 ps in all cases. Off-resonant pumping suppresses that contribution to the signal and singles out a signal, which is attributed to heating of the metal layer as well as transient desorption of the CO molecules. Due to the small photon energy (0.2 eV) used as pump pulses, the mechanism of desorption must be thermal, in which case the desorption yield depends exclusively on the fluence of absorbed light and not its wavelength. The thin Pt layers facilitate CO desorption, despite a relatively low pump pulse fluence, as they concentrate the absorbed energy in a small volume.

Published
2021

16. Markov state model of the two-state behaviour of water

Author

Hamm, Peter, University of Zurich, and Hamm, Peter

Subjects
10120 Department of Chemistry, Phase transition, Population, Analytical chemistry, General Physics and Astronomy, Markov process, 010402 general chemistry, Radial distribution function, 01 natural sciences, Critical point (mathematics), symbols.namesake, 540 Chemistry, 0103 physical sciences, Statistical physics, Physical and Theoretical Chemistry, education, Molecular diffusion, education.field_of_study, 010304 chemical physics, Markov chain, Chemistry, Atmospheric temperature range, 3100 General Physics and Astronomy, 0104 chemical sciences, symbols, 1606 Physical and Theoretical Chemistry
Abstract

With the help of a Markov State Model (MSM), two-state behaviour is resolved for two computer models of water in a temperature range from 255 K to room temperature (295 K). The method is first validated for ST2 water, for which the so far strongest evidence for a liquid-liquid phase transition exists. In that case, the results from the MSM can be cross-checked against the radial distribution function g5(r) of the 5th-closest water molecule around a given reference water molecule. The latter is a commonly used local order parameter, which exhibits a bimodal distribution just above the liquid-liquid critical point that represents the low-density form of the liquid (LDL) and the high density liquid. The correlation times and correlation lengths of the corresponding spatial domains are calculated and it is shown that they are connected via a simple diffusion model. Once the approach is established, TIP4P/2005 will be considered, which is the much more realistic representation of real water. The MSM can resolve two-state behavior also in that case, albeit with significantly smaller correlation times and lengths. The population of LDL-like water increases with decreasing temperature, thereby explaining the density maximum at 4 °C along the lines of the two-state model of water.

Published
2016

21. 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

Author

Hamm, Peter, University of Zurich, and Hamm, Peter

Subjects
10120 Department of Chemistry, Chemistry, Isotropy, General Physics and Astronomy, Molecular physics, 3100 General Physics and Astronomy, Force field (chemistry), Molecular dynamics, symbols.namesake, Polarizability, Molecular Response, 540 Chemistry, Water model, symbols, Physical and Theoretical Chemistry, Atomic physics, 1606 Physical and Theoretical Chemistry, Anisotropy, Raman spectroscopy
Abstract

In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.

Published
2014

50. Transient 2D IR spectroscopy from micro- to milliseconds

Author

Peter Hamm, University of Zurich, and Hamm, Peter

Subjects
10120 Department of Chemistry, Materials science, Infrared spectroscopy, General Physics and Astronomy, 010402 general chemistry, 01 natural sciences, law.invention, law, 0103 physical sciences, 540 Chemistry, Physical and Theoretical Chemistry, Millisecond, 010304 chemical physics, biology, business.industry, Amplifier, Bacteriorhodopsin, Laser, 3100 General Physics and Astronomy, 0104 chemical sciences, Pulse (physics), Femtosecond, biology.protein, Optoelectronics, Transient (oscillation), business, 1606 Physical and Theoretical Chemistry
Abstract

A new application of high-repetition rate, femtosecond Yb-laser/amplifier systems is introduced: transient 2D IR spectroscopy covering the time range from micro- to milliseconds. This approach intertwines the measurement of 2D IR spectra with the time separation from an actinic pump pulse and utilizes the high repetition rate of these lasers systems in two ways: by offering a high time resolution (10 µs) and by enabling the measurement of many 2D IR spectra. The well-studied photocycle of bacteriorhodopsin is used as a demonstration object in this proof-of-principle experiment.

Published
2021

Catalog

Books, media, physical & digital resources
See catalog results