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Martin Quack

Group Members

   Highlights

   Selected Lectures

Pictures

Teaching

    PC II Kinetics

    PC Advanced Kinetics

    Seminars (PC, Laser, C4)

Studies in

Interdisciplinary Sciences

Research topics

The group "Molecular Kinetics and Spectroscopy" of Martin Quack at ETH has as main research theme the understanding of fundamental, physical-chemical molecular primary processes. This research can be broadly classified in the following more detailed subfields.

     1. Intramolecular kinetics, vibrational redistribution, and energy
    transfer in polyatomic molecules and hydrogen bonded clusters
     from the sub-femtosecond to nanosecond time scales

as derived by analysis of high resolution infrared spectroscopy using an "indirect" experimental approach pioneered by the Quack group (making use of high frequency resolution and broadband coverage, but not high time resolution). This approach has shown that intramolecular rate processes of vibrational redistribution are often governed by specific properties of functional groups and thus can be transferred from one molecule to another. For instance in the alkyl CH chromophore redistribution occurs in 100 fs or less, whereas it is longer than ps in the seemingly similar acetylene chromophore or the hydrogen bonded (HF)₂ molecules and related larger clusters (HF)_n. Furthermore this approach has shown highly mode specific tunneling dynamics for hydrogen bond switching in (HF)₂ isotopomers as well as prototypical stereomutation dynamics in simple chiral molecules such as H₂O₂ or in CH₃OH and NH₃ isotopomers. These researches have fundamentally changed our thinking on intramolecular energy transfer in polyatomic molecules, replacing the earlier well established dogma of universally fast intramolecular equilibration on the subpicosecond time scale, which is the basis of statistical theories of chemical reactions (Quasi-equilibrium theory, QET, RRKM theory, transition state theory, statistical adiabatic channel model, SACM). Reviews: e, f, h, i, l, m, o, p, q, r, t (see below).

 

 2. Coherent infrared multiphoton excitation and laser chemistry of polyatomic molecules

Polyatomic molecules in the gas phase under intense infrared radiation from pulsed lasers can absorb many photons, typically 10 to 50, but even up to several hundred, in the case of C₆₀. Subsequent to this high vibrational excitation they will often react by decomposition or isomerisation, exceptionally, as in the case of C₆₀, by ionisation. In this research fundamental, quantitative aspects of these processes are studied in relation to a general quantitative theory originally developed by M. Quack in the 1978 – 82 period. Quantitative experimental tests of the theory are accompanied by applications of selective laser chemistry such as ¹³C/¹²C isotope separation, studies of state selected kinetics including hyperfine resolution and related processes. One long-term goal of the research is the development of tools for mode selective chemistry using also results from the research described under section 1. Infrared chromophores are systematically studied in relation to the "chromophore principle" of laser chemistry. Infrared laser chemistry has also some promise for possible industrial applications. Reviews: a, b, d, g, k, q, r, t.

     3. Spectroscopic studies of time resolved reaction kinetics on the  fs to μs time scale

complement the research discussed under sections 1. and 2. Recent advances should allow us to bridge the gap between our spectroscopic studies, which have in fact provided the first nontrivial, multidimensional, experimental femtosecond wavepacket dynamics, and the more widely used standard approaches of femtosecond kinetics by the well known and widely used pump-probe techniques. Reviews: k, q, t.

     4. Development of high resolution infrared spectroscopic methods for studies of intramolecular kinetics, atmospheric chemistry, and hydrogen bond cluster structure and dynamics

In these researches experimental tools are developed which allow for the analysis of very complex vibration – rotation spectra of polyatomic molecules. The application of these techniques range from the fundamental studies mentioned under section 1. to spectroscopic investigations of atmospheric pollution within an AGS project (Alliance for Global Sustainability). A major stumbling block in infrared gas phase spectroscopy in the past has been the inability to quantitatively analyze the complex very rich line spectra of polyatomic molecules with several "heavy" (i.e. non hydrogen) atoms. The Quack group has systematically developed experimental methods allowing for such analyses. Among these techniques we may mention the development of high resolution Fourier Transform Infrared – Supersonic Jet Spectroscopy over several "generations" of experimental apparatus, which allows simplification of spectra through jet cooling. Currently the worldwide highest resolution FTIR (Bruker prototype) spectrometer (resolving power 2 x 10⁶, experimental bandwidth 0.0007 cm^-1) is located in the laboratory of the group, in addition to an older BOMEM prototype system (0.004 cm^-1 bandwidth, full width half maximum, apodized). Another recent development is the still worldwide unique combination of tunable cw-diode laser cavity ring down spectroscopy, allowing for a resolving power of 2 x 10⁸ in the near infrared (experimental bandwidth about 1 MHz) with pulsed supersonic slit jet expansions. Further techniques applied in the group are lead-salt diode laser spectroscopy with supersonic jets and time resolved step-scan FTIR spectroscopy (at modest spectral resolution).

 

To demonstrate the need for such developments we may mention here just three out of many examples. Firstly, for atmospheric applications the important "atmospheric window" band of the Freon CFCl₃ could not in the past be rovibrationally analyzed in spite of many attempts. This problem was solved, using the techniques mentioned, by our group in a publication in 1995. Secondly for the whole class of chiral molecules (of necessarily a certain minimum complexity) there existed in the past (until about 1995) not a single case, where a rovibrational line analysis of an infrared gas phase band had been achieved. Today we have a few such analyses from recent work in our group (still the only ones worldwide, to our knowledge) such as CHFClBr, CDFClBr, Fluorooxirane CHFCH₂O, Dideuterooxirane (CD₂CH₂O), Difluoroallene, CHF=C=CHF, PF³⁵Cl³⁷Cl etc. Thirdly, the complex and weak overtone polyad absorption of (HF)₂ in the 7700 cm^-1 near infrared spectral range could only incompletely be analyzed in the past in spite of several attempts. Our group has recently achieved a full analysis of the polyad using the techniques mentioned. Reviews: e, m, q, t.

 

    5. Quantum theory of chemical reactions including tunneling   and infrared laser chemistry

We continue our long-term theoretical investigations on chemical reactions. The developments range from full (up to 6-dimensional) quantum wavepacket dynamics in simple (up to four atoms) reactions such as H₂O₂ stereomutation, (HF)₂ hydrogen bond dynamics, inversion in NHD₂, and related problems. We furthermore test and develop higher dimensional approximate techniques such as the quasiadiabatic channel reaction path hamiltonian method for tunneling reactions (for instance in CH₃OH or aniline-NHD, C₆H₅NHD etc.). We treat the full quantum dynamics of coherent infrared excitation. At the same time we develop approximate quantum statistical master equation approaches, which go beyond quasi-equilibrium statistical theories (RRKM, QET, SACM). The latter theories are also further developed in some of our work. Reviews: a, j, k, l, m, p, q.

 

    6. Theory of fundamental symmetry principles in chemical reactions and of parity violation in polyatomic (chiral) molecules

Starting with a fundamental paper on detailed symmetry selection rules in chemical reactions based on the principles of approximate nuclear spin symmetry and parity conservation in molecular processes (Mol. role of fundamental symmetry principles in molecular physics. Recent work has focussed on parity violation in chiral molecules. We have shown in recent years, that parity violating energy differences between enantiomers of chiral molecules are predicted by our newly developed theories to be typically one to two orders of magnitudes larger than anticipated on the basis of older theories. These findings have now also been confirmed by other groups and have important consequences for our attempts to measure this still very small energy difference   (Δ_RH₀ ≈ 10^-11 J mol^-1) calculated for CHFClBr, for example. A combination of experiment and theory in the future will be important for insights into the "Standard Model", a general theory of high energy particle physics. Indeed, the proposal for the most sensitive test of CPT symmetry so far made (with Δm/m =10^-30 compared to other current proposals and actual tests in the 10^-10 to 10^-20 range) stems from this work, although our investigations here can only be of preparatory nature, the final experimental CPT tests being envisaged using our spectroscopic developments in conjunction with high energy physics facilities such as CERN. We should make clear that this last aspect, while being of intellectual, scientific interest, has no practical short-term prospect. On the other hand, molecular parity violation in itself is of fundamental interest and actively investigated by the group. Reviews: c, f, n, s, t.

    7.  Useful reviews for more detailed overviews and summaries of the research of the Quack group for molecular kinetics and spectroscopy

a)           Reaction dynamics and statistical mechanics of the preparation of highly excited states by intense infrared radiation
M. Quack, Advances in Chemical Physics 50, 395-473 (1982) (K. Lawley, I. Prigogine and S. A. Rice, eds.)

b)           Infrared laser photochemistry
D.W. Lupo and M. Quack, Chem. Rev. 87, 181-216 (1987)

c)           Structure and dynamics of chiral molecules
M. Quack, Angewandte Chemie 101, 588-604 (1989), Angewandte Chemie (Intl. Ed.) 28, 571-586 (1989)

d)      Infrared laser chemistry and the dynamics of molecular multiphoton excitation
M. Quack, Infrared Physics 29, 441-466 (1989)

e)           Spectra and dynamics of coupled vibrations in polyatomic molecules
M. Quack, Annu. Rev. Phys. Chem. 41, 839-874 (1990)

f)           Molecular femtosecond quantum dynamics between less than yoctoseconds and more than days: Experiment and theory
M. Quack, chapter 27 in: "Femtosecond Chemistry", J. Manz and L. Woeste eds., Proc. Berlin Conf. Femtosecond Chemistry, Berlin (March 1993), Verlag Chemie, Weinheim (1994), p. 781-818

g)           Infrared laser chemistry
M. Quack, Infrared Phys. Technol. 36, 365-380 (1995)

h)           Molecular infrared spectra and molecular motion
M. Quack, J. Mol. Struct. 347, 245-266 (1995)

i)            Molecular spectroscopy and molecular dynamics: Theory and Experiment
M. Quack and W. Kutzelnigg, Ber. Bunsenges. Physik. Chem. 99, 231-245 (1995)

j)            Potential energy hypersurfaces for hydrogen bonded clusters (HF)_n
M. Quack and M. A. Suhm, in "Conceptual Perspectives in Quantum Chemistry",
415-463, E. S. Kryachko and J. L. Calais eds., Kluwer, Dordrecht 1997

k)           Multiphoton Excitation
M. Quack in "Encyclopedia of Computational Chemistry", Vol. 3, p. 1775-1791,
P. von Ragué Schleyer, N. Allinger, T. Clark, J. Gasteiger, P. A. Kollman, H. F. Schaefer III and P. R. Schreiner eds., John Wiley and Sons, 1998

l)            Statistical Adiabatic Channel Models
M. Quack and J. Troe, in "Encyclopedia of Computational Chemistry", Vol. 4,
p. 2708-2726, P. von Ragué Schleyer, N. Allinger, T. Clark, J. Gasteiger, P. A. Kollman, H.F. Schaefer III, P. R. Schreiner eds., John Wiley and Sons, 1998

m)         Spectroscopy and quantum dynamics of hydrogen fluoride clusters
M. Quack and M. A. Suhm, in "Advances in Molecular Vibrations and Collision Dynamics, Vol. III, Molecular Clusters", p. 205-248, Z. Bacic & J. Bowman eds.,
JAI press, Stamford, Conn. and London, England 1998 (ISBN: 1-55938-790-4)

n)           Intramolekulare Dynamik: Irreversibilität, Zeitumkehrsymmetrie und eine absolute Moleküluhr
M. Quack, Nova Acta Leopoldina 81, Neue Folge (No. 314) 137-173 (1999)

o)           Gas Phase Kinetics
D. Luckhaus and M. Quack
Encyclopedia of Chemical Physics and Physical Chemistry Vol. 1 (Fundamentals), Chapter A.3.4, pages 653–682 (IOP publishing, Bristol 2001, ed. by J. H. Moore and N. D. Spencer)

p)           Energy Redistribution in Reacting Systems
R. Marquardt and M. Quack
Encyclopedia of Chemical Physics and Physical Chemistry Vol. 1 (Fundamentals), Chapter A.3.13, pages 897–936 (IOP publishing, Bristol 2001, ed. by J. H. Moore and N. D. Spencer)

q)           Gas Phase Kinetics Studies
D. Luckhaus and M. Quack
Encyclopedia of Chemical Physics and Physical Chemistry Vol. 2 (Methods), Chapter B.2.5, pages 1871–1904 (IOP publishing, Bristol 2001, ed. by J. H. Moore and N. D. Spencer)

r)           Molecules in Motion
M. Quack
Chimia 55, 753–758 (2001)

s)           How Important is Parity Violation for Molecular and Biomolecular Chirality?
M. Quack
Angewandte Chemie 114, 4812–4825 (2002), Angew. Chem. Int. Ed. English 41, 4618-4630 (2002)

t)           Molecular spectra, reaction dynamics, symmetries and life (Paracelsus Prize lecture)
M. Quack,
Chimia, 57, 147–160 (2003)