Molecular fragmentation driven by ultrafast dynamic ionic resonances

Abstract

The authors time resolve molecular motion in bound state, ionic potentials that leads to bond cleavage during the interaction with intense, ultrafast laser fields. Resonances in molecular ions play an important role in dissociative ionization with ultrafast laser fields, and the authors demonstrate how these resonances evolve in time to produce dissociation after initial strong-field ionization. Exploiting such dynamic resonances offers the possibility of controlled bond breaking and characterizing time-dependent molecular structure.

Real-Time Probing of Structural Dynamics by Interaction between Chromophores

“…On the contrary the work on ultrafast dynamics of cations in the gas phase is rather limited. 1À10 In these experiments the pump pulse generates the cation by multiphoton ionization and absorption of the probe pulse induces increased fragmentation of the molecular ion, a scheme referred to as timeresolved ion photofragmentation (TRPF) by Ho et al 1 When the wave packet passes a region of the potential energy surface (PES) of the electronic state of the cation where the absorption cross section of the probe pulse is increased, sometimes called a "dynamic resonance", 4,6 absorption will lead to increased fragmentation of the molecular ion, either by direct means through dissociative states or in a statistical process as a consequence of excess internal energy. The position of these dynamic resonances depends on the shape of the PESs and the probe wavelength.…”

Communications: Photoinitiated bond dissociation of bromoiodomethane in solution: Comparison of one-photon and two-photon excitations and the formation of iso-CH2Br–I and iso-CH2I–Br

“…In addition, bromoiodomethane with two distinct carbon halogen bonds provides an opportunity for the careful investigation of optical control of chemical bond cleavage. 2 Early investigation of the photodissociation of CH 2 BrI in gas 3 and in molecular beams 4,5 demonstrated the ability to tune wavelength and modify the photoproduct formation. Control in linear absorption arises primarily from selective excitation.…”

“…2. Transient absorption spectra obtained for CH 2 BrI in 2-butanol following one-photon excitation at 266 nm or two-photon excitation at 405 nm. The top panel in each column shows the development of the photoproduct signal over the first 20 ps.…”

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

“…Also for these results no physical mechanism was reported to explain these results. Weinacht and co-workers [32][33][34] have recently reported several papers on the strong-field wave-packet driven dissociation and concerted elimination in CH 2 I 2 and ionic fragmentation in CH 2 BrI and CH 2 ClI. These experiments were carried out with 800 nm pulses with pulse intensities of 1-2ϫ 10 14 Watt/ cm 2 .…”

“…More recently, the group of Weinacht has reported several studies using pump-probe spectroscopy to study wavepacket dynamics and control in halomethanes. [32][33][34] From these multiphoton excitation studies at 800 nm, Weinacht and coworkers conclude that resonances between ionic surfaces of the parent ion facilitate the formation of ionic fragments.…”