Picosecond dephasing of coherently excited vibrations in liquid N 2/ar mixtures

Abstract

The dephasing time of the coherently excited molecular vibration of N 2 has been measured by a single high power laser pulse experiment via stimulated Raman scattering. In mixtures of liquid N 2 with Ar the surroundings of the excited N 2 molecules can be changed by varying the mole fraction of Ar in the mixture. In this way the influence of intermolecular interactions on the dephasing of vibrationally excited N 2 molecules can be studied. It turns out that the dephasing time is strongly dependent upon the mole fraction of Ar and varies from 90 ps in pure N 2 to 35 ps in almost pure Ar. The measured dephasing times are in good agreement with Raman linewidth measurements. Resonant V-V transfer between N 2 molecules does not contribute to the dephasing, but the dephasing is initiated by stochastic perturbations of the surrounding molecules.