Argon matrix isolation systems

In the laboratory 254 has inter alia been obtained in an argon matrix by irradiation of diazopropyne (253) at 10 K [106], Matrix isolation ESR and IR studies and ab initio calculations show it to be a 1,3-diradical with C2 symmetry, as indicated in Scheme 5.39 [107]. Irradiation with shorter wavelength light induces a 1,3-hydrogen shift by which the triplet propynylidene 254 is converted into the singlet propadienyli-dene 255, the parent system of unsaturated carbenes such as 251 (Scheme 5.39) [108]. 

Reedy Scientific sells a ClearIR GC/IR/MS system, which splits the GC (Thermo Finnigan Trace GC) effluent between an IR spectrometer (Thermo Nicolet Nexus 670), with a matrix isolation interface, and mass spectrometer (Thermo Finnigan s PolarisQ quadrupole ion trap or TRACE DSQ single quadrupole instrument). The GC effluent is mixed with 2 % argon. The mixture is directed to the surface of a cryogenically cooled rotating cylinder. 

In the past two years, we have been able to isolate four C2H2Si isomers in an argon matrix after pulsed flash pyrolysis of 2-ethynyl-l,l,l-trimethyldisilane [3]. As was proposed earlier, another access to the C2H2Si hypersurface consists of the reaction of silicon atoms with acetylene [5]. Based on this information about the C2H2Si isomers, it was obvious to take the Si/acetylene system to refine our silicon evaporation techniques. 

As mentioned earlier, conformational isomerization about the formal single bonds of polyene systems is facile in the ground state, where it occurs with activation barriers on the order of 2-4 kcalmol in acyclic systems". The process also occurs in acyclic dienes upon direct excitation, as was shown by SquiUacote and coworkers using low temperature matrix isolation techniques, at temperatures where thermal conformational reequilibration is suppressed (10-20 K) " . Thus, direct irradiation of tzaMi-l,3-butadiene in an argon matrix at 15 K results in the efficient formation of the cis -conformer, distinguishable from the irani-conformer by its distinct UV absorption and infrared... 

Gas Introduction and Matrix Formation. For introduction of gases for condensation and formation of matrices in the cryostat system, we employed two types of deposition technique SSO (Slow Spray-On) and PMI (Pulsed Matrix Isolation). In the SSO run, matrix gas (pure nitrogen, or argon) and sample were introduced slowly and separately into the setup via fine needle valves with micrometers. In the PMI (Pulsed Matrix Isolation) run, a mixture of matrix gas and sample(s) was introduced via electromagnetic valves controlled by a micro-computer. In PMI runs, not only was the deposition rate easily controlled over a wide range with good reproducibility, but a stratified matrix could also be prepared if two kinds of gas samples are introduced alternately and repeatedly. 

For infrared spectroscopic measurements at temperatures lower than 77 K, liquid helium is needed as the coolant instead of liquid nitrogen. The lowest temperature attainable is about 4 K. For matrix-isolation spectroscopy, a cryostat combined with a helium compressor for circulating cooled helium is commonly used. The lowest temperature attainable with such a system is about 15K, which enables the use of argon, krypton, and xenon, as well as nitrogen for matrix materials. 

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