Femtosecond observation of benzyne intermediates in a molecular beam: Bergman rearrangement in the isolated molecule

In this communication, we report our femtosecond real-time observation of the dynamics for the three didehydrobenzene molecules (p-, m-, and o-benzyne) generated from 1,4-, 1,3-, and 1,2-dibromobenzene, respectively, in a molecular beam, by using femtosecond time-resolved mass spectrometry. The time required for the first and the second C-Br bond breakage is less than 100 fs; the benzyne molecules are produced within 100 fs and then decay with a lifetime of 400 ps or more. Density functional theory and high-level ab initio calculations are also reported herein to elucidate the energetics along the reaction path. We discuss the dynamics and possible reaction mechanisms for the disappearance of benzyne intermediates. Our effort focuses on the isolated molecule dynamics of the three isomers on the femtosecond time scale.

The acceleration and collimation of jets.

I will discuss several issues related to the acceleration, collimation, and propagation of jets from active galactic nuclei. Hydromagnetic stresses provide the best bet for both accelerating relativistic flows and providing a certain amount of initial collimation. However, there are limits to how much "self-collimation" can be achieved without the help of an external pressurized medium. Moreover, existing models, which postulate highly organized poloidal flux near the base of the flow, are probably unrealistic. Instead, a large fraction of the magnetic energy may reside in highly disorganized "chaotic" fields. Such a field can also accelerate the flow to relativistic speeds, in some cases with greater efficiency than highly organized fields, but at the expense of self-collimation. The observational interpretation of jet physics is still hampered by a dearth of unambiguous diagnostics. Propagating disturbances in flows, such as the oblique shocks that may constitute the kiloparsec-scale "knots" in the M87 jet, may provide a wide range of untapped diagnostics for jet properties.