Dr. Michael F.A. Hippler

Research Interests

The aim of my research is the development of new methods and applications of ultra-sensitive, high-resolution laser spectroscopy to study the structure and dynamics of molecules and clusters. The understanding of intramolecular primary processes in polyatomic molecules at the fully quantum dynamical level remains among the most challenging research questions in physics and chemistry, with applications also in biology and environmental sciences. High-resolution spectroscopy is among the most powerful tools in advancing such research and it is crucial in this context to develop new and ever more powerful spectroscopic experiments.

In my work in Zürich, I successfully developed new experimental techniques for the infrared laser spectroscopy of gas-phase molecules. These techniques have been applied to the study of intramolecular vibrational energy redistribution, vibrational mode-specific tunnelling of hydrogen-bonded clusters and stereomutation dynamics. In one class of experiments, pulsed IR laser systems are used to excite vibrational transitions and a second, subsequent UV laser pulse to ionise the excited molecules. Ionisation detection of IR excitation has been coupled with a mass spectrometer thus adding a second dimension to optical spectroscopy. In another class of experiments, the extreme sensitivity of cavity-ring-down (CRD) spectroscopy (effective absorption path lengths of several km) is combined with the very high resolution of continuous wave (cw) diode lasers (100 kHz). This technique has been applied to measure accurately the transition strengths and weak overtone transitions of molecules (nitrous oxide, methane) and of hydrogen-bonded clusters (HF dimer).

So far in Sheffield, I have studied molecular association by FTIR, Raman spectroscopy and high-level quantum-chemical calculations. For this purpose, I set up a very sensitive stimulated Raman experiment with photoacoustic detection ('PARS'). Among the intermolecular forces, the hydrogen-bond X-H...Y is particularly relevant. A hydrogen bond usually exhibits a characteristic 'red'-shift (shift to lower wavenumbers) of the X-H stretching vibration, but more unconventional 'blue'-shifting hydrogen bonds also occur and have become a hot topic of current research. In Sheffield, I have recently studied some unusual, "blue-shifting" hydrogen bonds (e.g., CHCl3...SO2 in the gas phase and open HCOOH structures in liquid formic acid) by theory and experiment.

Teaching Section

Physical Chemistry

Undergraduate Courses Taught

• Chemical Reaction Kinetics (Year 1)
  This series of lectures develops an understanding of the factors governing chemical reactions and their rates and how this information can be used to predict reaction mechanisms.
• Theory of Spectroscopy (Year 2)
  This segment shows how it is possible to gain a detailed, accurate understanding of the energy levels of molecules by spectroscopy, and how this understanding can be used to extract information concerning fundamental problems (quantum theory), the population of quantum energy levels, the total concentration (analytical applications), the structure and the internal motions of molecules.
• Further Spectroscopy (Year 3)
  This segment discusses the understanding of electronically excited energy levels of atoms and molecules obtained by spectroscopy, in close connection with quantum theory. This understanding can be used to extract information concerning fundamental problems (quantum theory), population of quantum levels, total concentration (analytical applications), and the structure and dynamics of molecules. Together with the year 2 Rotational and Vibrational Spectroscopy unit, this module explains how UV-vis spectroscopy is connected to subjects as diverse as the process of vision, how lasers work, the origin of the orange/red colour of street lamps, and the composition of the universe.
• Advanced Spectroscopy and Theory (Year 4)
  Spectroscopy is at the heart of physical chemistry since it provides the most advanced tools to determine the structure and dynamics of molecules, for analytical applications and to test the foundations of theory. This segment gives an introduction into the theory of interaction between light and matter. It introduces some of the most sensitive and selective spectroscopic techniques, and works through selected examples where these techniques are used to extract structural and dynamic information, and to test theory.

Tutorial & Workshop Support

• First Year General Tutorials.
• Second Year Physical Chemistry Tutorials.
• Third Year Workshops.
• Third Year Literature Review.

Laboratory Teaching

• Second Year Laboratory Demonstrating
• Third Year Advanced Physical Chemistry Laboratory
• Fourth Year Research Project.