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Time-Resolved Infrared Spectroscopy of Water. Relation between the OH Stretching Frequency and the OO Distance

Bratos S., Leicknam J. -C., Pommeret S.

Polish Journal of Chemistry

2009

Vol. 83, nr 5

737-745

It is shown how infrared pump-probe spectroscopy can be used to measure subpico second variations of the oxygen-oxygen distribution function in liquid water. A diluted solution HDO/D2O rather than pure H2O is considered to switch off resonant vibrational interactions between water molecules; the local structure remains unchanged in this substitution. The present study is limited to times superior to 100–200 fs. This permits to avoid problems generated by hard sphere type collisions between water mole ules, as well as the interference between ultrafast pump and probe pulses. It is then shown that the Novak-Mikenda type relations between the OH stretching frequency and the OO distance largely sur vive when going from standard to ultrafast infrared spectroscopy. More over, the infrared pump-probe profiles of OH stretching bands closely parallel the oxygen-oxygen distribution functions in this time do main. Infrared pump-probe spectroscopy is thus a use ful substitute of time-resolved X-ray diffraction in this exceptional case.

Motion of hydrogen bonds in liquid water: direct observation in real time

Bratos S., Gale G. M., Gallot G., Hache F., Lascoux N., Leicknam J-Cl.

Bulletin of the Polish Academy of Sciences. Chemistry

1999

Vol. 47, No. 4

273-281

An experiment is described to study temporal variations of the hydrogen bond length in liquid water. The principles of this laser spectroscopic experiment are explained first. The construction of a laser source generating 150 fs pulses in the 2.5-4.4 um spectral region is detailed next. The theoretical analysis is proposed in terms of statistical mechanics of nonlinear optical processes. A new spectral effect is reported, the pump-probe delay dependent solvatochromic shift of the OH band. It is shown how this effect can be exploited to "photograph" the dynamics of the OH...O bonds in real time.