Synthesis of 5H-imidazo[2,1-c]pyrrolo[1,2-a][1,4]benzodiazepine

We have synthesized 5H-imidazo[2,1-c]pyrrolo[1,2-a][1,4]benzodiazepine 1 in five steps from 1-(2-amino-methylphenyl) pyrrole 4 . Amidino derivatives 11-12 have also been prepared.     

STM images of a large organic molecule adsorbed on a bare metal substrate or on a thin insulating layer: Visualization of HOMO and LUMO

An isomer of the methylterrylene molecule was adsorbed both on Cu(111) and on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). On the bare metal surface, the STM images do not reveal any intramolecular resolution and do not depend on the applied tunnel bias. On the contrary, the images acquired at specific bias voltages for the molecule on the salt layer show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.     

Laboratory scale-up of two-stage laser chemistry separation of13C from CF2HCl

The laboratory scale-up of a two-stage laser enrichment process for carbon isotopes, involving infrared multiphoton dissociation of freon-22, is described. Unmodified commercial equipment and materials were used. An initial study of the effect of fluence, laser frequency, freon-22 pressure and pressure of argon, nitrogen and trifluoromethyl chloride was made in short irradiation cells (constant fluence) in order to define optimum process parameters. The process was then scaled to higher throughput in longer cells (1–5 m) in which compensation for beam-energy depletion by absorption was made by reduction in the beam area by focussing. From the scale-up experiments, measurements of yield and enrichment of the tetrafluoroethylene product gave demonstrated production rates. These, coupled with measurements of the absorption, allowed extrapolation to production rates assuming total utilization of the available output energy.Using a 100 W TEA CO₂ laser (10 J, 10 Hz) we have demonstrated production rates of 0.20 g h^–1 carbon-12 at 99.99% carbon-12, 11 mg h^–1 carbon-13 at 72% carbon-13 and 2 kg per annum carbon-13 at 50%. Energy absorption measurements imply a capability to produce 3 kg per annum carbon-13 at over 95% carbon-13 in a two-stage process.The apparatus was used to produce gram quantities of carbon-13 depleted freon-22 (99.99% carbon-12). A comparison of the infrared multiphoton dissociation of this material with that of natural freon-22 (1.11% carbon-13) showed that under the conditions required to give selective dissociation of¹³CF₂HCl that¹²CF₂HCl was excited as a result of a dominantly radiative interaction and that collisional transfer from¹³CF₂HCl molecules played a minor role.Issued as NRCC 23639Summer Student 1983, Acadia University, N.S., Canada     

Controlling chaos in a fast diode resonator using extended time-delay autosynchronization: Experimental observations and theoretical analysis

We stabilize unstable periodic orbits of a fast diode resonator driven at 10.1 MHz (corresponding to a drive period under 100 ns) using extended time-delay autosynchronization. Stabilization is achieved by feedback of an error signal that is proportional to the difference between the value of a state variable and an infinite series of values of the state variable delayed in time by integral multiples of the period of the orbit. The technique is easy to implement electronically and it has an all-optical counterpart that may be useful for stabilizing the dynamics of fast chaotic lasers. We show that increasing the weights given to temporally distant states enlarges the domain of control and reduces the sensitivity of the domain of control on the propagation delays in the feedback loop. We determine the average time to obtain control as a function of the feedback gain and identify the mechanisms that destabilize the system at the boundaries of the domain of control. A theoretical stability analysis of a model of the diode resonator in the presence of time-delay feedback is in good agreement with the experimental results for the size and shape of the domain of control. (c) 1997 American Institute of Physics.