Ultrafast dynamics of strong-field dissociative ionization ofCH2Br2 probed by femtosecond soft x-ray transient absorptionspectroscopy

Journal Article · Tue Jan 15 04:00:00 EST 2008 · The Journal of Chemical Physics

OSTI ID:932710

Loh, Zhi-Heng; Leone, Stephen R

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{sub 2}Br{sub 2} induced by 800 nm strong-field irradiation. At moderate peak intensities (2.0 x 10{sup 14} W/cm{sup 2}), strong-field ionization is accompanied by ultrafast C-Br bond dissociation, producing both neutral Br ({sup 2}P{sub 3/2}) and Br* ({sup 2}P{sub 1/2}) atoms together with the CH{sub 2}Br{sup +} 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 Br/Br* population ratio is 8.1 {+-} 3.8 and that the Br {sup 2}P{sub 3/2} state is not aligned. The observed product distribution and the timescales of the photofragment appearances suggest that multiple field-dressed potential energy surfaces are involved in the dissociative ionization process. In addition, the transient absorption spectrum of CH{sub 2}Br{sub 2}{sup +} suggests that the alignment of the molecule relative to the polarization axis of the strong-field ionizing pulse determines the electronic symmetry of the resulting ion; alignment of the Br-Br, H-H, and C{sub 2} axis of the molecule along the polarization axis results in the production of the ion {tilde X}({sup 2}B{sub 2}), {tilde B}({sup 2}B{sub 1}) and {tilde C}({sup 2}A{sub 1}) states, respectively. At higher peak intensities (6.2 x 10{sup 14} W/cm{sup 2}), CH{sub 2}Br{sub 2}{sup +} undergoes sequential ionization to form the metastable CH{sub 2}Br{sub 2}{sup 2+} dication. These results demonstrate the potential of core-level probing with high-order harmonic transient absorption spectroscopy for studying ultrafast molecular dynamics.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director, Office of Science; National ScienceFoundation
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 932710
• Report Number(s): LBNL--63756; BnR: KC0301020
• Journal Information: The Journal of Chemical Physics, Journal Name: The Journal of Chemical Physics Journal Issue: 0 Vol. 0
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
ABSORPTION SPECTROSCOPY
ALIGNMENT
ATOMS
BROMINE
DISSOCIATION
DISTRIBUTION
HARMONIC GENERATION
HARMONICS
IONIZATION
IRRADIATION
POLARIZATION
POTENTIAL ENERGY
PRODUCTION
PULSE RISE TIME
SYMMETRY
TRANSIENTS