Coulomb explosion of propane in intense femtosecond laser fields

Abstract

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 C3 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.