Intramolecular vibrational dynamics in bis(trifluoromethyl)keten excited by resonant femtosecond IR radiation

Vibrational dynamics in different modes of (CF3)2CCO molecule induced by resonant femtosecond IR excitation of the ν1 mode is studied. Selective multiphoton excitation of this mode is observed up to the level v = 7. Intramolecular vibrational redistribution (IVR) causes relaxation of the ν1 mode with a time constant τIVR = 5 ps. The ‘instantaneous’ (τ ≪ τIVR) transient absorbance ΔOD signal at nonresonant modes ν2, ν3, and ν4 is revealed. Subsequent evolution of the ΔOD signal and the corresponding time constants are different for different modes, which we associate with different migration pathways of the vibrational energy.