Cooling of hot para-nitroaniline probed by non-resonant Raman scattering

Non-resonant anti-Stokes Raman probing of vibrational excitations following ultrafast (400 fs in methanol) internal conversion of para-nitroaniline is demonstrated. Immediately after this process an anti-Stokes signal blue shifted by 1290 cm−1 with respect to the probe laser pulse at 815 nm appears. The signal which is due to the NO2 stretch vibration moves to an anti-Stokes shift of 1315 cm−1 corresponding to the Stokes position of this vibration in 1 ps. The decay of this signal is slower and occurs within 3 ps. Possible origins of the strong initial red-shift of the anti-Stokes line are discussed.