Femtosecond Raman-induced polarisation spectroscopy of coherent rotationalwave packets: D-2, N-2 and NO2

Femtosecond Raman-induced polarisation spectroscopy of N-2, D-2 and NO2 was used to study the dynamics of coherent rotational wave packets in the grou nd electronic state with a time resolution similar to 50 fs. The periods of the observed signal beats agree with theoretical predictions. Special atte ntion was given to the effect of the pump light pulse chirp upon this dynam ics. For the N-2 and D-2 molecules, the sign and value of the chirp of the pump pulse affect the amplitude and form of the observed signal, while for NO2 influence of the chirp was not seen. This shows that the chirp is signi ficant for molecules with a large rotational constant. Evidence was obtaine d that for NO2 at short delay times the contribution to the signal is given by the vibrational wave packet in the excited electronic state on the back ground determined by the rotational dynamics in the ground state. (C) 1999 Elsevier Science B.V. All rights reserved.