Effect of solute orientation on solvation dynamics at the air/water interface

The ultrafast solvation dynamics of courmarin 314 (C314) molecules at the a ir/water interface has been shown to depend on their orientation with respe ct to the plane of the interface. A pump/second harmonic probe method using femtosecond laser pulses were used to measure the interface solvation dyna mics. The pump light was S polarized, i.e., in the interface plane, or P po larized, i.e., in the plane perpendicular to the plane of the interface. Th e S pumped C314 molecules yielded a solvation time of 820 +/- 60 fs, wherea s P pumped yielded a solvation time of 1215 +/- 90 fs. The interface inhomo geneous broadening on the solvation time scale is due to the differing orie ntations of C314 at the air/water interface.