Femtosecond velocity map imaging of concerted photodynamics in CF2I2

The femtosecond pump-probe technique is used in combination with velocity map ion imaging to study the photodissociation dynamics of CF2I2. Velocity map ion imaging provides the kinetic energy and the angular recoil distribution of the detected fragments. It enables us to distinguish between multiple photoexcitation and dissociation pathways leading to the same ionic fragment. For the dissociation of CF2I2 with delayed femtosecond pulses at 264 and 396 nm, various ionic fragments and dissociation channels are observed. Especially interesting dynamics is observed for the molecular detachment of I-2. It is found that at short pump-probe delay (less than or equal to250 fs) I-2(+) can be formed via a one-photon excitation at 264 nm and subsequent ionization of the dissociating neutral CF2I2 molecule. This excitation pathway produces slow I-2(+) fragments recoiling predominantly parallel along the polarization of the 264 nm pump laser. At long delay time (greater than or equal to500 fs) this pathway is closed and the formation of molecular I-2(+) proceeds via a two-photon excitation at 264 nm to a highly electronically excited state of the CF2I2 molecule. The molecular detachment of I-2 is via a concerted asynchronous dissociation producing a highly internally excited I-2(*) fragment, possibly in the (2)Pi(3/2)5d;2g state. The highly excited I-2 fragments are ionized by a single 396 nm photon producing I-2(+) fragments. The kinetic energy of this pathway is higher and the I-2(+) fragments are recoiling perpendicular with respect to the polarization of the pump laser. (C) 2002 American Institute of Physics.