Recent work from our group (Lozovoy, V. V.; Zhu, X.; Gunaratne, T. C.; Harris, D. A.; Shane, J. C.; Dantus, M. J. Phys. Chem. A2008, 112, 3789) using shaped nonresonant femtosecond pulses to ionize and fragment polyatomic molecules indicated that pulse duration is the most important parameter for controlling the relative yield of different fragment ions. Here we explore the time-resolved dynamics that ensue following the interaction of the molecules with a strong 10(15) W/cm(2) nonresonant near-infrared laser field. The data reveal that most of the fragmentation processes occur well after ionization. The molecular dynamics are followed in the 10(-14)-10(-10) s time scale. Studies carried out on acetophenone derivatives are used to assign the observed modulation in the benzoyl product ion yield, which is found to correlate with further ionization and fragmentation through electronic coordination. The resulting experimental data, together with photoelectron spectra and the electron-ionization mass spectra of these compounds, allow us to propose ladder switching processes taking place in this family of compounds which regulate the different fragment ions observed. This analysis sheds light on how pulse duration influences the yield of different fragment ions.
Recordings of magnetic fields, thought to be crucial to our solar system’s rapid accretion, are potentially retained in unaltered nanometric low-Ni kamacite (~ metallic Fe) grains encased within dusty olivine crystals, found in the chondrules of unequilibrated chondrites. However, most of these kamacite grains are magnetically non-uniform, so their ability to retain four-billion-year-old magnetic recordings cannot be estimated by previous theories, which assume only uniform magnetization. Here, we demonstrate that non-uniformly magnetized nanometric kamacite grains are stable over solar system timescales and likely the primary carrier of remanence in dusty olivine. By performing in-situ temperature-dependent nanometric magnetic measurements using off-axis electron holography, we demonstrate the thermal stability of multi-vortex kamacite grains from the chondritic Bishunpur meteorite. Combined with numerical micromagnetic modeling, we determine the stability of the magnetization of these grains. Our study shows that dusty olivine kamacite grains are capable of retaining magnetic recordings from the accreting solar system.
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