Accession Number : AD0432781

Title :   PHOTO-INDUCED PHASE CHANGES IN LOW-TEMPERATURE GLASES,

Corporate Author : AEROSPACE CORP EL SEGUNDO CALIF

Personal Author(s) : Siegel,Seymour ; Judeikis,Henry S.

Report Date : 12 FEB 1964

Pagination or Media Count : 24

Abstract : The uv irradiation of ether and ethanol at 77 K leads to the formation of trapped ethyl radicals via an excited impurity-solvent interaction. The radicals were observed by the use of electron paramagnetic resonance (EPR) spectroscopy both during the irradiation and during the postirradiation period. The spectral shape changed as a function of time upon light extinction and also of temperature during irradiation. The qualitative kinetics of the spectral changes were examined in some detail. The following model is proposed to explain the experimental observations: The radicals are formed surrounded by a metastable local high-temperature phase region (corresponding to an equilibrium temperature > 115 K). In this high-temperature phase region, there is more freedom for internal rotation or other molecular motions (but no translation). The metastable phase is maintained because the impurity still absorbs energy from the radiation field which is subsequently dissipated into heating the local environment. The resultant high temperatures are quickly quenched, thereby trapping the hightemperature phase. Light extinction leads to a decay of the high-temperature phase into one of two more stable, but also more rigid, phases, leading to changes in the shape of the radical EPR spectra. (Author)

Descriptors :   (*ULTRAVIOLET RADIATION, FREE RADICALS), (*FREE RADICALS, CRYOGENICS), ELECTRONS, PARAMAGNETIC RESONANCE, PHASE STUDIES, TRANSITION TEMPERATURE, EXCITATION, IMPURITIES, HEAT OF ACTIVATION, LINE SPECTRA, ETHERS, ALCOHOLS

Distribution Statement : APPROVED FOR PUBLIC RELEASE