Ultrafast strong-field dissociative ionization dynamics of CH2Br2 probed by femtosecond soft x-ray transient absorption spectroscopy

Abstract

Femtosecond time-resolved soft x-ray transient absorption spectroscopy based on a high-order harmonic generation source is used to investigate the dissociative ionization of CH(2)Br(2) induced by 800 nm strong-field irradiation. At moderate laser peak intensities (2.0 x 10(14) Wcm(2)), strong-field ionization is accompanied by ultrafast C-Br bond dissociation, producing both neutral Br ((2)P(32)) and Br(*) ((2)P(12)) atoms together with the CH(2)Br(+) fragment ion. The measured rise times for Br and Br(*) are 130+/-22 fs and 74+/-10 fs, respectively. The atomic bromine quantum state distribution shows that the BrBr(*) population ratio is 8.1+/-3.8 and that the Br (2)P(32) state is not aligned. The observed product distribution and the time scales of the photofragment appearances suggest that multiple field-dressed potential energy surfaces are involved in the dissociative ionization process. At higher laser peak intensities (6.2 x 10(14) Wcm(2)), CH(2)Br(2) (+) undergoes sequential ionization to form the metastable CH(2)Br(2) (2+) dication. These results demonstrate the potential of core-level probing with high-order harmonic transient absorption spectroscopy for studying ultrafast molecular dynamics.

Reconstruction of an excited-state molecular wave packet with attosecond transient absorption spectroscopy

“…With the availability of high-resolution VUV spectrometers [15], one can conceivably monitor the recurrence of the vibronic wave packet created close to a localized reaction center, even in solution. ATAS has already been applied successfully to selected studies of strongfield ionization [5] and dissociation [16], wave-packet motion [3,4,6,17,18], and correlated electron dynamics [19][20][21][22], as well as phase transition dynamics in condensed matter [23,24], with unprecedented energy and time resolution. As ATAS encodes both the amplitudes and phases of interacting states, reconstruction and control of an electron wave packet-in both space and time-has been achieved [22].…”

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation

“…As we are describing our approach with femtosecond resolution we shall concentrate in the following on femtosecond pulses from High Harmonic Generation (HHG) (1,2,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). The applications of such pulses range from spectroscopy (1,2,(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) to microscopy (28,29) and coherent diffraction or holography (30)(31)(32)(33). In most cases, HHG is performed with a driving-laser wavelength of around 800 nm and HHG pulses with photon energies between 15 and 100 eV are used.…”

Femtosecond extreme ultraviolet ion imaging of ultrafast dynamics in electronically excited helium nanodroplets

“…Laboratory-based high-order harmonic generation (HHG) driven by intense femtosecond infrared (IR) lasers is employed to study the evolution of UV-excited molecular states [1], [2], to disentangle the quantum state distribution in strong fieldionized systems [3], [4], and to monitor the ionization and relaxation dynamics of EUV-excited atoms and molecules [5]- [10]. Here, we combine a HHG light source with state-of-the-art 3-D momentum-resolved ion mass spectrometry to investigate the relaxation dynamics of electronically excited helium nanodroplets.…”