Vibrational relaxation following ultrafast internal conversion: comparing IR and Raman probing

• DOI: 10.1016/j.cplett.2004.05.090
• Publication Date: 2004-06-17T17:05:21Z
• Authors: T Schrader; A Sieg; F Koller; W Schreier; Q An; W Zinth; P Gilch
• Keywords: Picosecond; Vibrational energy relaxation; Rotational–vibrational coupling; Two-dimensional infrared spectroscopy

Abstract Femtosecond IR and Raman techniques are compared with respect to their abilities to monitor vibrational relaxation following ultrafast internal conversion. The study was performed on para -nitroaniline which undergoes sub-picosecond internal conversion to the ground state populating a variety of vibrational modes. The NO 2 stretch vibration at 1315 cm −1 responds to the excitation by a strong red shift, visible in transient IR and Raman experiments. It is due to the off-diagonal anharmonic coupling with other modes. The population of the NO 2 stretch mode itself can only be observed in the (anti-Stokes) Raman spectrum, whereas IR spectroscopy is superior in detecting the coupling induced shift.