title: Coherent control of the ultrafast dissociative ionization dynamics of bromochloroalkanes.
abstract: We report on the coherent control of the ultrafast ionization and fragmentation dynamics of the bromochloroalkanes C(2)H(4)BrCl and C(3)H(6)BrCl using shaped femtosecond laser pulses. In closed-loop control experiments on bromochloropropane (C(3)H(6)BrCl) the fragment ion yields of CH(2)Cl(+), CH(2)Br(+), and C(3)H(3)(+) are optimized with respect to that of the parent cation C(3)H(6)BrCl(+). The fragment ion yields are recorded in additional experiments in order to reveal the energetics of cation fragmentation, where laser-produced plasma radiation is used as a tunable pulsed nanosecond vacuum ultraviolet radiation source along with photoionization mass spectrometry. The time structure of the optimized femtosecond laser pulses leads to a depletion of the parent ion and an enhancement of the fragment ions, where a characteristic sequence of pulses is required. Specifically, an intense pump pulse is followed by a less intense probe pulse where the delay is 0.5 ps. Similarly optimized pulse shapes are obtained from closed-loop control experiments on bromochloroethane (C(2)H(4)BrCl), where the fragment ion yield of CH(2)Br(+) is optimized with respect to that of C(2)H(4)BrCl(+) as well as the fragment ion ratios C(2)H(2)(+)/CH(2)Br(+) and C(2)H(3)(+)/C(2)H(4)Cl(+). The assignment of the underlying control mechanism is derived from one-color 804 nm pump-probe experiments, where the yields of the parent cation and several fragments show broad dynamic resonances with a maximum at Δt = 0.5 ps. The experimental findings are rationalized in terms of dynamic ionic resonances leading to an enhanced dissociation of the parent cation and some primary fragment ions.
authors: Physikalische und Theoretische Chemie, Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany. j.plenge@fu-berlin.de
authors: J
authors: J
authors: Plenge
authors: A
authors: A
authors: Wirsing
authors: I
authors: I
authors: Wagner-Drebenstedt
authors: I
authors: I
authors: Halfpap
authors: B
authors: B
authors: Kieling
authors: B
authors: B
authors: Wassermann
authors: E
authors: E
authors: Rühl
mesh_terms: D004980:Ethane / Q000031:analogs & derivatives* / Q000737:chemistry; D006846:Hydrocarbons, Halogenated / Q000737:chemistry*; D007834:Lasers; D013058:Mass Spectrometry; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry; D013997:Time Factors
chemical_list: D006846:Hydrocarbons, Halogenated; C039590:1-bromo-2-chloroethane; C560814:1-bromo-3-chloropropane; D004980:Ethane; D011407:Propane