Chains In Solid State Research Articles

Using Crystal Optics to Demonstrate Single-Layer Localization of a Solid-State Chain Reaction

Upon warming to 225 K, single crystals of 11-bromoundecanoyl peroxide (BrUP), in which radicals have been created by photolysis at lower temperature, undergo partial decomposition by a radical chain reaction ca. 40 cycles long. FTIR allowed monitoring two chain products: CO2 and an α-lactone that decomposes further at 260 K. When initiation is confined to alternate molecular layers by polarized photoselection, the chain reaction reduces the crystal symmetry from tetragonal to monoclinic. Desymmetrization is easily observed by optical microscopy, although it is difficult to detect by X-ray diffraction. Accurate monitoring of birefringence using a Sénarmont 1/4-wave plate, and comparison with FTIR kinetics, proves that the chain reaction occurs within single molecular layers 2 nm thick.

Solid-state Chain Photochlorination in Recrystallized Mixtures of Ethene and Chlorine at 30 K

Binary solid films of chlorine with ethene have been deposited in excess argon and subsequently recrystaliized by warmingand evaporation of the argon solvent. This novel recrystallization procedure results in a dramatic increase in the quantumyield and degree of conversion for long stereospecific chain photochlorination with the exclusive formation of thefrans-1,2-dichloroethane.

Isomeric product distributions from solid-state chain reactions and low-temperature microexplosions of acetylene and chlorine

Free radical chain reaction of acetylene and chlorine is initiated by pulsed ultraviolet laser photolysis of disordered solid films of these reagents at 10-60 K. The product (identified by FTIR spectroscopy) is a mixture of Z (cis) and E (trans) isomers of 1,2-dichloroethene. At 60 K in an equimolar mixture of reagents the photochemical quantum yield is 25±4; the isomeric product distribution is [E]/[Z]= 10.2 ± 1.5

IR study of the cholesteryl n-alkanoates conformation mobility

IR-spectroscopy methods have been used to study conformational mobility of alkyl chains of cholesteryl alkanoates in different phases. It is shown that cholesteryl alkanoates may be divied into three groups with similar conformation and packing of alkyl chains in solid state and mesomorphism types within each of them.

Excited-state proton-transfer polymerization of amorphous formaldehyde

In this communication, the authors report that chain polymerization of formaldehyde can be initiated by excited-state proton transfer from 2-nitrophenol. This molecule has a pK/sub a/ of 9.1 in the ground state, but upon absorption of a photon the molecule is estimated to have a pK/sub a/ of about /minus/0.6 in the S/sub 1/ state excited at 308 nm. The authors believe this to be the first example of a solid-state chain reaction which is initiated by proton transfer from an electronically excited dopant molecule. The technique is extremely powerful because it provides a way of temporarily generating a strong acid within a solid for the purpose of inducing transient or irreversible chemical reactions. Photochemical generation of acids has previously been shown by other workers to be useful for photolithography by inducing depolymerization and/or dissolution of polymeric photoresists. Photoacids are also known to induce cationic polymerization of several different monomers in liquid solutions. All of the previous work has involved chemical rearrangements which form the acid in its ground state.

Noise spectrum characteristics of low-noise microwave tubes and solid state devices

In this paper experimental data on the FM and AM noise of low-noise microwave tubes, and solid-state chains of the types used in Doppler radars are presented. The tube types include magnetrons, klystrons, and triodes. Data on solid-state chains of the type consisting of a VHF crystal-controlled transistor oscillator, followed by a VHF transistor power amplifier, and a varactor frequency multiplier are also presented. The spectral shape of the solid-state chain is shown to differ from those of the microwave tubes and that of the klystron. Comparisons are made between the various devices.