Excitation and dissociation of polyatomic molecules under the action of femtosecond infrared laser pulses

Abstract

The effect of high-intensity femtosecond laser pulses (100–200 fs) in the near (0.8–1.8 µm) and medium (4.6–5.8 µm) IR ranges on the CF2HCl, CF3H, (CF3)2C=C=O, and C4F9COI molecules is examined. Irradiation of CF2HCl and CF3H molecules by 0.8-to 1.8-µm laser pulses with intensities of >40 TW/cm2 (>4 × 1013 W/cm2) makes them dissociate to yield CF3H and CF4, respectively. The key mechanism of the dissociation of these molecules is field ionization and fragmentation. The excitation of the stretching vibrations of the C=O bond in the (CF3)2C=C=O and C4F9COI molecules by 4.5-to 5.8-µm femtosecond pulses produced no detectable dissociation up to a fluence of ∼0.5 J/cm2 (or a intensity of ∼2.5 TW/cm2). Probable explanations of this observation are discussed.