MOLECULAR KINETICS AND SPECTROSCOPY
  THE GROUP OF MARTIN QUACK AT ETH ZURICH

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Latsis Symposium

Meeting of Martin's 60th

 

 

Highlights of research results (1997 – 2015)

 

We summarize here in short words in form of a punch line some of the highlights of the research results of the group in the period mentioned. The numbered references [189, …] can be found in the following lists of publications (full list of publications), whereas letters [a, b, c, …] refer to reviews cited in the research section.

 

1.           We have achieved the first quantitative rovibrational "quantum state resolved" full analyses of high resolution infrared spectral bands of chiral molecules with the examples fluorooxirane and CHFClBr [189, 193]. The development of the methods in this context opens the route for many further such analyses (some already underway) and paves the way for quantum state selected experiments on molecular parity violation [c, s, 206, 243].

 

2.           The theoretical discovery by our group, reported and elaborated in detail in [206] (first reported by us briefly in 1996), that parity violating effective potentials in (chiral) polyatomic molecules are typically by one to two orders of magnitude larger than anticipated on the basis of older theories has fundamentally changed the outlook also for possible experiments on this still very small effect [s].

 

3.           Further theoretical confirmation on the much increased parity violations mentioned under 2. was essential and achieved with quite an independent and more advanced approach developed by our group [220]. Meanwhile other groups have been able as well to confirm our results independently, and thus the theoretical results can be considered firm.

 

4.           One consequence of the theoretical tensor structure of parity violating potentials discussed by us [206], together with the order of magnitude increased absolute values of the tensor elements, is the complete refutation of all quantitative results and conclusions based on the older theories prior to 1995. In particular, the widely publicized earlier results on stabilization of L-aminoacids by parity violation (and possible consequences for the evolution of homochirality in life) have been explicitly refuted for alanine [230].

 

5.           We have reported the first quantitative calculations on vibrational-rotational frequency shifts in polyatomic molecules by parity violation [222] (first reported at IUPAC Congress 1999).

6.           We have reported the first case (dichlorodisulfane Cl2S2) where it could be shown quantitatively that parity violation dominates over tunneling in typical chiral molecules [243] (see also [s] for the discussion of qualitative expectations). This leads to the perhaps surprising conclusion that the dynamics of all ordinary chiral molecules that are stable against racemisation at room temperature are in fact dominated by parity violation (as opposed to tunneling) in spite of the small absolute magnitude of this effect.

 

7.           We have reported the first case of vibrational ionization after infrared multiphoton excitation of a neutral polyatomic molecule (C60 [195]).

 

8.           The sensitivity of multidimensional wavepacket dynamics upon small errors introduced by approximate effective hamiltonian analyses of intramolecular vibrational redistribution in spectra of polyatomic molecules was demonstrated for the example of CHFClBr [191], which in addition shows numerous interesting dynamical effects under coherent, mode selective IR-multiphoton excitation. This has important consequences for conclusions drawn from the very widely used effective hamiltonian analyses and strengthens the case made by us earlier on the basis of eigenstate and coupling constant analyses [e].

 

9.           For the dimer (HF)2 of the hydrogen fluoride we have derived an analytical full dimensional potential hypersurface of essentially spectroscopic accuracy, which still to date seems the first and only such example [205]. This has use for related approximate approaches on larger clusters (HF)n [196] and opens the way to develop accurate many body potentials for higher clusters [240], which may ultimately allow us an accurate description of condensed phases based on microscopic spectroscopic results in the gas phase [j, m].

10.        Global full dimensional potential hypersurfaces for the theory of spectroscopy and reaction dynamics were also developed for H2O2 [217] (6d) and methane [211] (9-dimensional). An important first application concerned full 6-dimensional quantum wavepacket results for the tunneling stereomutation of hydrogen peroxide H2O2 [213]. These show a high degree of mode selectivity even with excitations well above the barrier for stereomutation. The prototype inversion dynamics of NHD2 shows mode selective tunneling with coherent infrared excitation of various non-inversion modes even high above the barrier for inversion, which is the first dynamical calculation of this kind [255] (see also experiments in [259]).

 

11.        Experiments on infrared multiphoton excitation of methanol have demonstrated for the first time the case C/B transition on the master equation theory [a] of infrared multiphoton excitation [254] as a function of internal molecular energy by preexcitation.

 

12.        Mode selective tunneling is a most characteristic feature of methanol conformational (torsional) dynamics. Excitation of the OH stretching excitation to high energies inhibits torsional tunneling [258].

 

13.        We have developed isotopomer (and mass) selective high resolution infrared spectroscopy, which allows one to determine separately the infrared spectra of each isotopomer (or molecule with associated mass) in a mixture of several isotopomers (or compounds of different mass) even at very high dilution in supersonic jets. The application to Aniline-NHD reveals mode selective picosecond stereomutation dynamics by tunneling [207].

 

14.        The development of cw-laser cavity ring down spectroscopy in conjunction with pulsed supersonic jet expansions has allowed the very accurate determination of a band center of a high lying combination tone in methane [249]. Such results can in the future provide constraints on the potential hypersurfaces [211].

 

 

 


Comments  and suggestions to:
Csaba Fábri
ETH Zürich, Laboratorium für Physikalische Chemie
ETH Hönggerberg, HCI, CH-8093 Zürich