Solvent-dependent vibrational relaxation pathways after successive resonant IR excitation to υ = 2
1996
Abstract With two subsequent resonant intense picosecond infrared pulses, we have succeeded in pumping a significant fraction of iodoform molecules in solution to the second vibrationally excited state of the CH stretching mode. Transient populations of the vibrational levels are monitored with weak probe pulses. From these pump-pump-probe experiments, we find that the subsequent relaxation route depends critically on the solvent. In a strongly polar solvent (acetone) relaxation from υ = 2 to υ = 0 occurs predominantly via the υ = 1 state, with time constants of T 1 2→1 = 10 ± 5 and T 1 1→0 = 60 ± 5 ps, respectively. In contrast, in a less polar solvent (chloroform) direct decay to the ground state is observed, with a time constant ( T 1 2→0 = 80 ± 20 ps), comparable to the energy lifetime of the first excited state ( T 1 1→0 = 125 ± 5 ps).
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