Structure, Dynamique et Spectroscopie de Clusters Ioniques. Synergie entre expériences IR-PD et simulations DFT-MD. – SPIONCLUS

The experiment developed in the Lisy group is unique and brings a new possibility of detailed conformational mapping of clusters’s conformers and energy barriers, within the gas-phase community. By combining mass spectrometric methods with infrared laser spectroscopy, Prof. Lisy helped pioneer the field of ion cluster spectroscopy. Prof. Lisy’s insistence that cluster internal energy (or effective cluster temperature) is crucial to understanding cluster structure and conformation has changed the way the others in the field now approach these systems. The Gaigeot group brings originality in the emerging field of DFT-MD to the experimental facets of the research that desperately need accurate anharmonic vibrational frequencies, potential energy barrier heights and vibrational energy relaxation. The expertise of the group in theoretical spectroscopy using MD simulations and its coupling to action spectroscopy experiments is unique in Europe. The association between the two groups will bring novelty and excellence to the domain of vibrational spectroscopy of strongly anharmonic molecular ions.

Major results obtained over the first 18 months of SPIONCLUS :

The structures of Cl--(Methanol)1-2 clusters have been unraveled combining Infrared Predissociation (IR-PD) experiments and DFT-based molecular dynamics simulations (DFT-MD) at 100K . The dynamical IR spectra extracted from DFT-MD provide the initial 600 cm-1 large anharmonic red-shift of the O-H stretch from uncomplexed methanol (3682 cm-1) to Cl--(Methanol)1 complex (3085 cm-1) as observed in the IR-PD experiment, as well as the subtle supplementary blue- and red- shifts of the O-H stretch in Cl--(Methanol)2 depending on the structure.
[Paper In Press, 2013, Spectro. Chimica Acta A: Molecular and Biomolecular Spectroscopy, dx.doi.org/10.1016/j.saa.2013.05.073] :

IRPD spectra of Cl (NMA)1(H2O)0 2Ar2 combined with BOMD dynamical IR spectra clearly show that the chloride ion is bound to the amine hydrogen, forming a strong ionic hydrogen bond. The dynamical spectra of Cl (NMA)1(H2O)0 2 complexes show that the interpretation of the IR-PD spectra can be achieved unambiguously, as these theoretical spectra naturally provide the initial 500-600 cm-1 red-shift of the NH stretch from NMA to NMA complexed with Cl-, and the subsequent supplementary 100 cm-1 red-shifts when adding water molecules. This is achieved without any rescaling factors.
[Paper In Press, 2013, Phys. Chem. Chem. Phys., DOI:10.1039/C3CP52418C ] :

We have developped experimental and theoretical tools to follow the formation of high energy conformers of clusters, including a full comprehension of the processes occuring during their formation. This has been demonstrated on Li+(H2O)3-4 clusters. The synergy is made between IR-PD experiments [Prof Lisy’s group, USA] and DFT-MD trajectories [Prof Gaigeot’s group, France] simulating the collisions between the metal ion and the water clusters (4 ps timescale) complemented with RRKM calculations (microseconds timescale).
[Paper In preparation]

We continue our project following the outlines described above for biologically relevant systems of interest.

Publications about the project during the first 18 months by the french team of ANR SPIONCLUS (international peer reviewed journals) :

O-H anharmonic vibrational motions in Cl-(CH3OH)1-2 ionic clusters. Combined IRPD experiments and AIMD simulations.
J.P. Beck, A. Cimas, J.M. Lisy, M.P. Gaigeot
2013, In Press, Spectro. Chimica Acta A: Molecular and Biomolecular Spectroscopy,
DOI: dx.doi.org/10.1016/j.saa.2013.05.073

Anharmonic vibrations from the Chloride...Amide ionic hydrogen bonds in Cl-(N-methylacetamide)1(H2O)0-2Ar2 cluster ions. Combined IRPD experiments and AIMD simulations.
J.P. Beck, M.P. Gaigeot, J.M. Lisy
2013, In Press, Phys. Chem. Chem. Phys.,
DOI:10.1039/C3CP52418C

Results presented in 6 international conferences + 3 national conferences