Imaging of ultrafast molecular elimination reactions

Ultrafast molecular elimination reactions are studied using the velocity map ion imaging technique in combination with femtosecond pump-probe laser excitation. A pump laser is used to initiate the dissociative reaction, and after a predetermined time delay a probe laser interrogates the molecular system. Ionic fragments are detected with a two-dimensional velocity map imaging detector providing detailed information about the energetic and vectorial properties of mass selected photofragments. In this paper we discuss the ultrafast elimination of molecular iodine, I-2, from IF2C-CF2I, where the iodine atoms originate from neighboring carbon atoms. By varying the femtosecond delay between pump and probe pulse, it is found that elimination of molecular iodine is a concerted process, although the two carbon-iodine bonds are not broken synchronously. Energetic considerations suggest that the crucial step in this fragmentation process is an electron transfer between the two iodine atoms in the parent molecule, which leads to Coulombic attraction and the creation of an ion-pair state in the molecular iodine fragment.