PICOSECOND TIME-RESOLVED RAMAN-SPECTROSCOPY OF S1 P-TERPHENYL AND P-TERPHENYL-D14 IN SOLUTION - TIME-DEPENDENT CHANGES OF RAMAN BAND SHAPES

The picosecond time-resolved Raman spectra of p-terphenyl and its deuterated analogue (d14) in the first excited singlet (S1) electronic state were observed in heptane and acetonitrile solutions. The most intense band in the S1 p-terphenyl at 750 cm-1 is assigned to an in-plane ring vibration based on the shift on the deuteration. The peak position and the bandwidth of the 750 cm-1 band change as the time delay between the pump and probe pulses changes. The initial changes in the position and width appear between 0 and 5 ps, which can be attributed to the strong electric fields of the pump and probe light pulses. After the initial changes are over, the position and the width of the 750 cm-1 band change gradually to their stationary values until about 30 ps. These changes are probably due to the cooling of the solute-solvent system. Similar changes are recorded for two other Raman bands at 993 and 1018 cm-1.