Hirotomo Hase

Electronic Spectra of Trapped Electrons in Organic Glasses at 4°K

The optical absorption spectra of trapped electrons were observed in γ‐irradiated ethylene glycol–water, methanol, 10M NaOH, and MTHF at 4°K. The prominent infrared absorption bands were observed in ethylene glycol–water and ethanol glasses, while the bands in methanol, 10M NaOH, and MTHF glasses were similar in shape, slightly red shifted, to the bands for the radiolysis at 77°K. When the glasses were warmed to 77°K, the bands changed irreversibly into those for the radiolysis at 77°K, reducing the absorption intensity. The spectral changes at the intermediate temperatures between 4°K and 77°K were recorded for ethylene glycol–water and methanol cases. The results are interpreted by the molecular reorientation model proposed in the previous paper [T. Higashimura, M. Noda, T. Warashina, and H. Yoshida, J. Chem. Phys. 53, 1152 (1970)].

Trapped Electrons Produced in Ethanol Glass at 4°K

Optical absorption and ESR measurements were carried out on et− produced in ethanol at 4°K. The same et− yield for γ radiolysis at 4 and 77°K indicates that electrons are stabilized in pre‐existing traps at 4°K where molecular dipoles remain unrelaxed. et− prior to solvation can be classified into two groups. One with λmax = 1500 nm, W1/2= 4 × 103 cm−1 and Δ Hpp = 5.5 ± 0.5 G is easily photobleached by the infrared light. The other with broad absorption band in the visible and Δ Hpp = 13.5 ± 1.5 G is not photobleached by the infrared light. The successive shift of the absorption spectrum to the higher energy side on warming is interpreted by the molecular reorientation mechanism. et− decay is observed during the solvation process, depending on time required for the solvation. The blue shift of the absorption spectrum on reducing the temperature is attributed to contraction of electron traps.

Trapped electrons in crystalline D2O ice at 4°K

The ir absorption band and EPR spectrum of ΔHpp=1.3 G at g?2 observed in irradiated D2O crystalline ice at 4°K have been assigned to trapped electrons. The ir band and EPR spectrum decayed with τ1/2=35 min in pure D2O ice at 4°K. The trapped electrons were not observed in H2O ice at 4°K. Addition of 1.5% H2O in volume in D2O reduced the trapped electron yield to about 60% and shortened τ1/2. Effect of NH4F and AgNO3 doped in D2O ice has been examined. The trapped electrons were stable in 10M LiCl⋅H2O–D2O glass at 4°K. Stability of the trapped electrons in ice has been discussed.

Silver atom solvation and desolvation in ice matrices: Electron spin resonance studies of radiation‐produced silver atoms formed at 4 K

Silver ions rd by electrons at 4 K in aqueous matrices produce silver atoms with an Ag+ solvation shell. Brief warming to 77 K causes complete solvation of Ag0 which appears to correspond to water molecule rotation around an OH bond to hydrogen bond with Ag0. This atom solvation process can be reversed by optical excitation at 400 nm in the Ag0 absorption band.(AIP)

Electronic spectra of trapped electrons in organic glasses at 4°K. 3-methylpentane, 3-methylhexane and methylcyclohexane

Abstract The spectra of e − t produced in 3-MP and MCH at 4°K were at longer wavelengths than those at 73°K, and shifted back to the same position as those produced at 73°K when the glasses were warmed to 73°K. The spectra in 3-MHX at 4 and 73°K were the same.

Hydrogen atom abstraction reaction by H atoms in γ-radiolysis and U.V.-photolysis of alkane mixtures at 4K

Abstract Hydrogen atom abstraction reaction by H atoms in the irradiated alkane mixtures has been studied at 4 K by ESR spectroscopy. When H atoms are produced by the radiolysis of neopentane, 2,2,3,3-tetramethylbutane, or isobutane at 4 K, they react promptly with the neighboring solvent molecules, though they react selectively with the solute alkane at 77 K. When H atoms are produced by the photolysis or by the dissociative electron attachment of HI in neo-C 5 H 12 matrix, they react selectively with the solute alkane at 4 K as well as at 77 K. This suggests that the H atoms produced by the photolysis of HI at 4 K migrate a longer distance than those produced by the radiolysis of the solvent alkane at 4 K. Mechanisms of H atom abstraction reaction are discussed.

Photo-Induced Trapped Electron in Rigid Media : Photobleaching Study in the Mixed Polar Solvents

An experimental study has been made on the optical absorption spectra on the photobleaching process of trapped electron ( e t - ) produced by photoionization of tryptophan in mixed polar solvents at 77°K. The population of e t - is decreased on the photobleaching process in these solvents according to the law which can be always expressed as the sum of two first-order decays. Two kinds of traps formed in the polar solvents have been shown to exist although the explicit mode of the trap is not clear. An assumption is presented that exchange of trapping of electron occurs between two traps on the photobleaching process of e t - .

Effects of atomic hydrogen and annealing temperatures on some radiation-induced phenomena in differently originated quartz

Abstract The existence of atomic hydrogen besides intense Al-centers was ascertained in ESR spectrum measurements of a variety of natural quartzes after irradiation at 77 K. The remarkable decrease of the Al-hole center signals, coincident with the complete disappearance of ESR-signal due to atomic hydrogen, was observed upon heating to room temperature. A positive correlation was established between the atomic hydrogen signals and the reducing proportion of the Al-hole centers. Additionally, the thermal annealing treatments of the quartz samples beyond 800°C before irradiation induced the significant decrease of H 0 as well as the removal of OH absorbance in IR-spectra around 3500 cm −1 . On the basis of these experiments, it was confirmed that the atomic hydrogen derived from the radiolysis of OH-related impurities could operate as a “killer” of radiation-induced Al-centers, presumably main holes of blue thermoluminescence (BTL). These results play an important role in the phase-transition temperature of β -quartz/tridymite on the TL-property changes. The red thermoluminescence (RTL)-related centers were also searched using ESR spectra with the aid of the annealing experiments.

Electronic spectra of C70 anions produced in γ-irradiated organic glasses at 77 K

Abstract The electronic spectra of C70 anions were observed in γ-irradiated methylcyclohexane and MTHF glasses at 77 K. The band at 1386 nm in methylcyclohexane was assigned to C−70. The spectrum in MTHF consisted of two bands at 1184 and 1377 nm. The former band was tentatively ascribed to C2−70. The values of ϵG obtained are 265±40, 230±45 and 217±45 M−1 cm−1 at 1386, 1377 and 1184 nm, respectively.

Comparative ESR study of C60 and C70 radical anions produced in γ-irradiated organic solid solutions at 77 K

Abstract ESR spectra of C 70 radical anions were detected for C 70 /methylcyclohexane (MCHX) and C 70 /2-methyltetrahydrofuran (MTHF) solid solutions which were γ-irradiated at 77 K and subsequently annealed at 107–117 K. The ESR spectrum for C 70 /MCHX was a singlet which was ascribed to C 70 − , and was flanked by a pair of satellites due to matrix proton spin flip lines. The ESR spectrum for C 70 /MTHF was a superposition of a singlet and a deformed doublet. The latter was unstable and disappeared at 109 K, and was tentatively ascribed to C 70 2− . ESR spectra of C 60 radical anions were partly reinvestigated and are compared to those of C 70 . The relative electron attachment efficiencies for C 60 and C 70 at 77 K were estimated, and the former was about twice as large as the latter. Isothermal decay at 77 K was observed for both C 60 and C 70 radical anions.