PICOSECOND DYNAMICS OF EOSIN-B AT THE AIR WATER INTERFACE BY TIME-RESOLVED 2ND-HARMONIC GENERATION - ORIENTATIONAL RANDOMIZATION AND ROTATIONAL RELAXATION/

Time-resolved surface second harmonic generation has been used to stud y the picosecond dynamics of the dianion Eosin B dye molecule at the a ir/water interface. It is found that the induced second harmonic signa l depolarization obtained with the perturbation of the distribution of Eosin B molecules at the interface can be attributed to an out-of-pla ne rotational diffusion motion of the molecules. The data also suggest that the high Fox er densities of the laser pulses randomize the orie ntation distribution of the molecules at the interface. A rotational d iffusion time of 90 +/- 20 ps is measured, a value significantly faste r than the one obtained in bulk aqueous phases. (C) 1998 Elsevier Scie nce B.V. All rights reserved.