Excitation and dissociation of molecules by femtosecond IR laser radiation in the gas phase and on dielectric surfaces

This paper presents an overview of early studies and new experimental data on the effect of near-IR (0.8 — 1.8 μm) and mid-IR (3.3—5.8 μm) intense femtosecond (130 — 350 fs) laser pulses on polyatomic molecules in the gas phase and on the surface of substrates. We examine the vibrational dynamics of nine molecules containing a C = O chromophore group, which are initiated by resonance femtosecond IR laser radiation at a wavelength of ~5 μm, and report measured characteristic times of intramolecular vibrational redistribution. The characteristic time of molecules containing a single C = O group lies in the range 2.4 — 20 ps and that of the Fe(CO)₅ and Cr(CO)₆ molecules lies in the nanosecond range (~1.0 and ~1.5 ns, respectively). Carbon structures have been observed for the first time to result from the decomposition of (CF₃)₂CCO molecules on the surface of metal fluorides under the effect of femtosecond IR laser radiation in the wavelength range 3.3 — 5.4 μm with no gas-phase decomposition of the molecules.