Tracking vibrational energy transfer and molecular dynamics in nitromethane and nitromethane/methanol mixed solutions by ultrafast spectroscopy

Vibrational dynamics and energy transfer were identified by femtosecond time- and frequency-resolved coherent anti-Stokes Raman scattering spectroscopy. Nitromethane (NM) was selectively and collectively excited in an orderly manner. The beating modes involving vibrations were described and the dephasing time of theses vibrational modes was monitored. The results indicated that intramolecular vibrational energy transfer was governed by vibrational couplings. When the NM/methanol mixed solutions were collectively excited, no evidence for a beat or intermolecular energy transfer was found because hydrogen bonds acted as a molecular damper yielding a faster decay of molecular dynamics.