Feshbach resonances in the water molecule revealed by state-selective spectroscopy

We employ triple-resonance vibrational overtone excitation to access quasibound states of water from several fully characterized bound states of the molecule. Comparison of the measured dissociation spectra allows a rigorous assignment of rotational quantum numbers J, nuclear spin and parity and a tentative vibrational characterization of the observed resonances. Their asymmetrical shapes (Fano profiles) reflect interference of dipole moments for transitions to these resonances with that to the dissociative continuum. The assignments and Fano profile parameters of the resonances stand as a benchmark for the extension of accurate quantum-mechanical calculations to activated complexes of water. The narrow widths of some of these resonances indicate that water molecules may survive for as long as up to 60 ps in states above the dissociation threshold. We consider the possible implication of such long-lived states for the kinetics of water dissociation and the OH+H association reaction.

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

This work deals with the engineering of a new luminescent complex of lanthanide, able to be specifically grafted onto biological materials and to emit a characteristic light useful in quantifying the concentration of the target molecules. We have based our molecular design on TbL1, wich possesses a significant quantum yield in water pointing to an efficient intramolecular energy transfer. We have elaborated the synthesis of a ligand derived from L1 and named L3, by functionalizing one of the chromophoric groups into a moiety able to couple the luminescent sensor to biological materials. The synthesis of the complexes was then realized. The thermodynamic study of the ligands L1 and L3, and their terbium complexes in water was made to establish the distribution diagrams and to compare their behaviour, especially at neutral pH. In addition, EuL1 was also investigated and the complexation constants of TbL1, EuL1 and TbL3 in water showed that these molecules are thermodynamically stable in aqueous media. Characterization of EuL3 in the solid state by high resolution luminescence allowed us to determine the geometry of the coordination sphere of the Eu(III) ion, which possesses a distorded C4 symmetry. The detailed study of the Eu(III) ion transitions evidenced two different sites, possibly arising from an equilibrium induced by the competition between a water molecule and the carboxylate function. This interpretation is in line with the measured lifetimes of the Tb(III) and Eu(III) excited states and the calculation of the hydration number of the complexes in aqueous solution. The determination of the energy of the singlet state and triplet states of the ligand, as well as of the emitting levels of the Ln(III) ions in solution showed that their relative values are favorable for a good intramolecular energy transfer. The quantum yields of TbL3 and EuL3, which amount to 2.6 % and 1.4 %, respectively, are lower than those of the complexes with L1, denoting that the presence of the acid function increases losses in the energy transfer. However, these values remain sizeable enough for potential biomedical applications. The study of the intermolecular energy transfer from EuL1, EuL3 and TbL3 to the acceptor Cy5 has proved promising, and the resulting yields were 90 % for EuL1 and 80 % for the complexes with L3.

EPFL2004

Quantitative State-Selective Spectroscopy of Water Below and Above the First Dissociation Limit

Maxim Grechko

We use triple resonance vibration overtone spectroscopy to characterize quantum states of water with up to 19 quanta of stretching vibration – the last stretching state below dissociation. State-selectivity, offered by the triple resonance in conjunction with theoretical predictions allows unambiguous assignment of the observed ro-vibrational transitions. Totally 38 new vibrational states and about 360 rotation-vibration energy levels are characterized. These levels span the energy region from 35 500 cm-1 above the vibrational ground state up to the first dissociation limit of the molecule D0 = 41 145.94±0.15 cm-1. In order to increase the number of observed transitions we employ collisionally assisted double/triple-resonance overtone spectroscopy (CADROS/CATROS). In this approach we admit rotational relaxation of water molecules at intermediate levels of double/triple-resonance excitation scheme. Two CADROS-type spectra, for ortho and para water, were measured in the energy region of the vstr = 10 vibrational manifold. Totally 81 new rotation-vibration levels were obtained from these spectra. We extend the use of triple resonance excitation to access states of water above D0. From known assignment of the employed gateway states we perform strict assignments of the nuclear spin and parity of the observed resonances. By comparison of measured dissociation spectra we strictly derive the rotational quantum number J and perform tentative vibrational characterization of quasi-bound states of water. We fit asymmetric shapes of the observed resonances by Fano profiles. The assignments and Fano profile parameters stand as a benchmark for extension of accurate quantum-mechanical calculations to activated water complexes. We consider the possible implication of the observed quasi-bound states for the kinetics of water dissociation and the OH+H association reaction. We finally performed measurements of Stark coefficients for J = 2 rotational levels in vibrational states within an energy region from 27 500 to 40 984 cm-1, using a combination of triple resonance overtone excitation with photofragment detection and with Stark induced quantum beat spectroscopy. We compare these data with the Stark coefficients, calculated using the most recently developed dipole moment surface and two different potential energy surfaces.

EPFL2010

Dynamics of individual rotational states in an electrostatic guide for neutral molecules

Benjamin Bertsche, Andreas Osterwalder

The guiding properties of individual rotational states of deuterated ammonia inside an electrostatic hexapole guide are presented. The guide is combined with resonance enhanced multiphoton ionization detection to assess the guiding probabilities and velocity distributions as a function of the rotational quantum numbers J and K. Due to the differences in the effective dipole moment these states are prepared at significantly different translational temperatures. A model is presented that describes the velocity-distribution for individual M-sublevels, and this model is also used to determine a rotational-state dependent translational temperature. Furthermore, the hexapole field has been replaced by a dipole field in order to obtain a band-pass velocity filter. However, the resulting change in the final velocity distribution is similar to that obtained from a hexapole guide but with increased backing pressure, leading to collisional acceleration of the slow molecules.

2011

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

EPFL2004

Quantitative State-Selective Spectroscopy of Water Below and Above the First Dissociation Limit

Maxim Grechko

EPFL2010