Coulomb explosion of propane in intense femtosecond laser fields

Femtosecond laser-induced Coulomb explosion of C3H8 is investigated experimentally by means of time-of-flight mass spectrometry at different intensities. The mass spectrum of C3H8 presents much more abundant fragments than obtained through electron-impact ionization. The appearance of intermediate daughter molecular ions with a double-peak structure shows that Coulomb explosion of C3H8 undergoes a two-step process. One C-C bond of the C-3 carbon skeleton breaks first and then the other C-C bond breaks. The ion yields and initial kinetic energy releases of ionic fragments increase with increasing laser intensity. The C2+ and H-2(+) ions exhibit anisotropic angular distributions, with a maximum along the laser polarization vector and a minimum perpendicular to it. The geometric alignment is the main reason for the measured anisotropic angular distributions of ionic fragments. A significant decrease of ionization occurs in circular polarization and elliptical polarization. This fact reveals that field-induced ionization is responsible for the formation mechanism of molecular ions.