Ethanol Glass Research Articles

Effect of irradiation at 77 K prior to irradiation at 4 K in ethanol glass: A further evidence of solvation of trapped electrons at 77 K

The yield of shallowly trapped electrons in ethanol glass at 4 K decreases with previous irradiation dose at 77 K, whereas the total yield of trapped electrons at 4 K does not decreases significantly. This is an evidence of the solvation of trapped electrons at 77 K.

Éffets des interactions intermoléculaires par liaison hydrogène sur l'absorption et la luminescence des amines aromatiques en matrice vitreuse a 77 K

The spectral properties of a series of aromatic amines (aniline, p-toluidine, dimethylaniline, N,N′- p-phenylenediamine (PPD), N,N,N′,N′-tetramethyl- p-phenylediamine (TMPD), diphenylamine, diphenylparaphenylenediamine in organic glasses at 77 K have been studied. The results obtained in two typical solvents, a non-polar one, methylcyclohexane, and a hydroxylic one, ethanol, indicate that solute—solvent and solute—solute H-bond associations play an important role in the phosphorescence intensity and lifetime. The various kinds of associations and their effect on the solute conformation are discussed. It is also shown that aniline, PPD and TMPD may be protonated in ethanol glasses, this is interpreted as being due to the enhancement of the solute—solvent H-bond in a rigid medium.

Spin relaxation of triplet pyrene in a crystal and in a glass

We have investigated the EPR spectral lines of the photo-excited triplet state of pyrene-d-10 both in a fluorene single crystal and an ethanol glass matrix. In the crystal we have measured the width, shape and saturation parameters, λ′, a and B 1/2 u , of the ΔM = 1 lines from both sites in the cleavage plane, Y-Z, at 193 K and along the principal directions, X, Y, Z, between 143 K and 300 K. In the glass the same parameters have been measured for the six resonances of the absorption derivative at 77 K. We have used a general deconvolution procedure to extract the unresolved inhomogeneous and homogeneous broadenings, ΔB G and ΔB L ≡ 1/γT 2, and the spin-lattice relaxation rate, T 1 -1, from λ′, a and B 1/2 u for the different types of resonances. The use of Fourier-series expansions permits optimal utilization of the data and resolution of the terms of different symmetries for these quantities. The application of the method of moments, using assumed spin densities, permits the demonstration that the main ...

An Upper Limit to the Excited Electron-Cation Recombination Lifetimes of Trapped Electrons in Ethanol and 2-Methyl-tetrahydrofuran Glasses at 4 and 77 K

Abstract N,N,N′,N′-Tetramethyl-p-phenylenediamine (TMPD) fluorescence lifetimes in 2-methyltetrahydrofuran (MTHF) glass at 77 K (13.5 ns) and in ethanol glass at 77 K (12.3 ns) and 4 K (11.5 ns) were measured using 347 nm excitation from a frequency doubled ruby laser. Trapped electrons and TMPD+ were generated in these matrices by photoionization and the recombination fluorescence stimulated by 694 nm laser light was found, within an experimental limit of 1 ns, to occur with the same lifetime as the directly excited fluorescence. A convolution analysis indicates that the electron-cation recombination lifetimes are ≤1 ns in all these matrices at the temperatures given. It is also suggested that a lower limit for the electron mobility of 0.005 cm2 V−1 s−1 is implied by these data.

Temperature dependence of eiectron spin-lattice relaxation of radiation-produced silver atoms in polycrystalline aqueous and glassy organic matrices. Importance of relaxation by tunneling modes in disordered matrices

The electron spin-lattice relaxation of trapped silver atoms in polycrystalline ice matrices and in methanol, ethanol, propylene carbonate, and 2-methyltetrahydrofuran organic glasses has been directly studied as a function of temperature by the saturation-recovery method. Below 40 K the dominant electron spin-lattice relaxation mechanism involves modulation of the electron nuclear dipolar interaction with nuclei in the radical's environment by tunneling of those nuclei between two nearly equal energy configurations. This relaxation mechanism occurs with high efficiency, has a characteristic linear temperature dependence, and is typically found in highly disordered matrices. The efficiency of this relaxation mechanism seems to decrease with decreasing polarity of the matrix. Deuteration experiments show that the tunneling nuclei are protons and in methanol it is shown that the methyl protons have more tunneling modes available than the hydroxyl protons. In polycrystalline ice matrices silver atoms can be stabilized with two different orientations of surrounding water molecules; the efficiency of the tunneling relaxation reflects this difference. From these and previous results on tunneling relaxation of trapped electrons in glassy matrices it appears that tunneling relaxation may be used to distinguish models with different geometrical configurations and to determine the relative rigidity of such configurations around trapped radicals in disordered solids.

Photoconductivity of presolvated electrons in ethanol glass at 4 K

Photoconductivity of localized electrons, which are not solvated, in γ-irradiated ethanol glass at 4 K was studied. Photocurrents of 10 −13 A or larger were stably detected in the wavelength range of 900–2200 nm. The wavelength dependence of the photocurrent reveals that pre-solvated electrons probably have no bound excited states.

Laser photoionization study of time dependent spectral shifts of localized electrons in ethanol glass. Temperature effects

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLaser photoionization study of time dependent spectral shifts of localized electrons in ethanol glass. Temperature effectsMasaaki Ogasawara and Larry KevanCite this: J. Phys. Chem. 1978, 82, 4, 378–382Publication Date (Print):February 1, 1978Publication History Published online1 May 2002Published inissue 1 February 1978https://doi.org/10.1021/j100493a002RIGHTS & PERMISSIONSArticle Views16Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (659 KB) Get e-Alerts

Excess electrons in condensed media: Theory of optical absorption spectrum in molecular solutions

A theoretical formalism is developed for analyzing the spectra of excess electrons in pure molecular solids and liquids. A perturbation decomposition of the Hamiltonian allows the expression for the band shape I (ω) to be written as a sum of a zeroth order part, proportional to dipole transition matrix elements and corresponding Franck–Condon factors, and perturbation terms containing effects of electron hopping and their fluctuations. By using several physically motivated approximations (e.g., the temporally localized nature of electronic transitions which allows a short-time expansion of the time dependence of operators), the expression for I (ω) can be expressed in terms of solvent structure information and the electron–solvent interaction potential. From the general expressions for I (ω) a simplified model was developed in the special case of systems for which bound-to-bound transitions are dominant. This model has been successfully applied to the spectra of excess electrons in ethanol and anthracene glass, thereby providing some optimism for the potential use of the general formalism derived here.

Éffets des interactions intermoléculaires par liaison hydrogène sur l'absorption et la luminescence des amines aromatiques en matrice vitreuse A 77 K

The spectral properties of a series of aromatic amines (aniline, p-toluidine, dimethylaniline, N,N'- p-phenylenediamine (PPD), N,N,N',N'-tetramethyl- p-phenylediamine (TMPD), diphenylamine, diphenylparaphenylenediamine in organic glasses at 77 K have been studied. The results obtained in two typical solvents, a non-polar one, methylcyclohexane, and a hydroxylic one, ethanol, indicate that solute—solvent and solute—solute H-bond associations play an important role in the phosphorescence intensity and lifetime. T various kinds of associations and their effect on the solute conformation are discussed. It is also shown that aniline, PPD and TMPD may be protonated in ethanol glasses, this is interpreted as being due to the enhancement of the solute—solvent H-bond in a rigid medium.

Temperature dependence of the recombination fluorescence of photoionized indole and N,N,N',N'-tetramethyl-p-phenylenediamine in organic glasses. Consequences of electron tunneling and diffusion

The recombination fluorescence seen when TMPD is photoionized in methylcyclohexane, 3-methylhexane, and 2-methyltetrahydrofuran glasses and when indole is photoionized in 2-propanol and ethanol glasses has been investigated. The initial intensity and decay rate of the recombination fluorescence decreases as the UV irradiation temperature is increased from temperatures below the glass transition temperature T/sub g/ of the matrix. This is interpreted in terms of electron tunneling to the cation in which the tunneling barrier height or electron trap depth increases slightly (0.05 to 0.2 eV) with increasing irradiation temperature. By considering how the matrix polarity affects the degree of electron trap deepening as well as the electron trap depth relative to the excited singlet level of the solute, we are able to understand the difference in magnitudes and their changes for the initial decay rate and the initial recombination fluorescence. At temperatures 10 to 30 K above T/sub g/, depending on the matrix polarity, diffusive recombination dominates tunneling recombination and produces a peak in the recombination fluorescence unless the electron trap depth has dropped below the excited singlet of the solute. Thus, this type of experiment offers a simple diagnostic for distinguishing tunneling and diffusive recombination of electrons with cations inmore » disordered matrices.« less

Fluorescence spectra of chlorophyll-alpha and chlorophyll-b from site selection spectroscopy.

Abstract— …Highly resolved fluorescence spectra of chlorophyll‐a and ‐b have been measured in ethanol and methyltetrahydrofuran glasses at ˜4K. The vibrational frequencies measured are independent of solvent and were highly reproducible, ±1cm‐1 or less. A possible use of this experimental technique as an analytical tool is discussed.

An electron spin-lattice relaxation mechanism involving tunneling modes for trapped radicals in glassy matrixes. Theoretical development and application to trapped electrons in .gamma.-irradiated ethanol glasses

A new electron spin-lattice relaxation mechanism for molecular radicals in glassy matrices is developed theoretically and tested experimentally. The mechanism depends on modulation of the electron nuclear dipolar interaction between a trapped radical and nearby magnetic nuclei by the motion of tunneling nuclei or groups of nuclei in the disordered glass. In glassy systems it appears that modulation by tunneling modes is much more effective than modulation by lattice phonos for electron spin-lattice relaxation in low and intermediate temperature ranges, typically to approximately 100 K. The quantitative mechanism predicts: (a) that the spin-lattice relaxation rate T/sub 1//sup -1/ is linearly proportional to temperature, (b) that T/sub 1//sup -1/ is dependent on glass preparation to the extent that this affects the number and distribution of tunneling groups, (c) that T/sub 1//sup -1/ is sensitive to the isotopic composition of the glass, (d) that T/sub 1//sup -1/ for a given radical is larger by several orders of magnitude in a glassy environment than in a crystalline one, and (e) that T/sub 1//sup -1/ varies as ..omega../sup -2/ where ..omega.. is the EPR frequency. Predictions (a) to (d) have been tested and supported by T/sub 1/ measurements vs. temperature on trapped electrons inmore » C/sub 2/H/sub 5/OH, C/sub 2/D/sub 5/OH, and C/sub 2/H/sub 5/OD glasses. The measurements were made with a pulsed EPR spectrometer by the saturation recovery technique.« less

Electron spin-lattice relaxation mechanisms of radiation produced trapped electrons and hydrogen atoms in aqueous and organic glassy matrices: modulation of electron nuclear dipolar interaction by tunnelling modes in a glassy matrix

The spin lattice relaxation of trapped electrons in aqueous and organic glasses and trapped hydrogen atoms in phosphoric acid glass has been directly studied as a function of temperature by the saturation recovery method. Below 50 to 100 K, the major spin lattice relaxation mechanism involves modulation of the electron nuclear dipolar(END) interaction with nuclei in the radical's environment by tunnelling of those nuclei between two or more positions. This relaxation mechanism occurs with high efficiency and has a characteristic linear temperature dependence. The tunnelling nuclei around trapped electrons do not seem to involve the nearest neighbour nuclei which are oriented by the electron in the process of solvation. Instead the tunnelling nuclei typically appear to be next nearest neighbours to the trapped electron. The identities of the tunnelling nuclei have been deduced by isotopic substitution and are attributed to: Na in 10 mol dm–3 NaOH aqueous glass, ethyl protons in ethanol glass, methyl protons in methanol glass and methyl protons in MTHF glass. For trapped hydrogen atoms in phosphoric acid, the phosphorus nuclei appear to be the effective tunnelling nuclei. Below ∼10 K the spin lattice relaxation is dominated by a temperature independent cross relaxation term for H atoms in phosphoric acid glass and for electrons in 10 mol dm–3 NaOH aqueous glass, but not for electrons in organic glasses. This is compared with recent electron–electron double resonance studies of cross relaxation in these glasses. The spin lattice relaxation of O– formed in 10 mol dm–3 NaOH aqueous glass was also studied and found to be mainly dominated by a Raman process with an effective Debye temperature of about 100 K.

The phosphorescence of Group I and Group II metal acetylacetonates in ethanol glass at 77 K

The phosphorescence spectra of the Group I and Group II metal acetylacetonates (Metal = Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba) have been measured in solid ethanol glass solutions at 77 K and found to have profiles similar to that of Al(aa)3. The phosphorescence decays are non-exponential and this behaviour is attributed to the presence of both coordinated and free acetylacetonate anion. Time resolved spectroscopy and other considerations indicate that the energies of the lowest excited ligand singlet and triplet states of the aa− ion are, unlike the triplet state lifetime, little affected by coordination. Solvolysis is reported in ethanol solution which invalidates some previously reported spectral parameters.

Heavy atom effect in diamagnetic metal acetylacetonates

Spectral data are presented for acetylacetonate complexes of eighteen diamagnetic closed shell metal ions. The nature of the metal ion has relatively little effect on the absorption and phosphorescence energies, but has a very marked effect on the phosphorescence lifetime, τ, in solid ethanol glasses at 77 K. The possibility that the observed variations in τ are the result of an intramolecular heavy atom effect is examined. Comparison of τ with ligand 1H n.m.r. resonances indicate that a significant degree of heavy atom induced spin–orbit coupling occurs only with the Th4+, Lu3+, La3+ and In3+ complexes. In the other cases it is suggested that the principal factor in determining τ may be the energy difference between the Tπ,π* and Tn,π* states and a specific model is proposed.

Electron solvation in alcohols at 77 K after pulse radiolysis

The presence of benzyl in 1-propanol, 2-propanol and ethanol glasses at 77 K markedly affects the changes which occur in the absorption spectra of the trapped electrons in the pure alcohols after their production by pulse radiolysis. The well known growth in the visible is considerably reduced while the decay in the far red is unaffected. It is concluded that the spectral changes arise by “trap-hopping” of the electrons induced by thermal excitation from the initial shallow traps, rather than solvent re-orientation.

Triplet EPR of fluorobenzonitriles

The triplet EPR spectra of the three monofluorobenzonitriles in ethanol glasses at ≈90 K have been compared. Ortho- and meta-fluorine merely broaden the Δ M = 2 signals, whereas para-fluorine produces a 54 G splitting. In accord with simple symmetry considerations, the 3L a state of benzonitrile is predominately a 1,4-diradical with little free spin density at the ortho and meta positions.

Gamma radiolysis of 3-methylpentane and ethanol glasses containing triphenylamine

Gamma irradiation of a 3-methylpentane (3MP) glass containing triphenylamine (TPA) at 72–74K produces the trapped electron (e 3MP −) and another negative species (e TPA −). Like e TPA − absorbs in the I.R. with a peak at 1.6 μm. In contrast with e 3MP −, e TPA − is not bleached by 1.9 μm light, has a narrower absorption band, and exhibits a broader E.S.R. singlet with ΔH ms = 6.6 G . At 72K, the 100 eV yield, G(e TPA −), increases with increase in TPA concentration and has the value 1.3 at 10 −2 mol dm −3 TPA while G(e 3MP − decreases from 0.4 in neat 3MP to 0.1 at 10 −2 mol dm −3 TPA. Gamma irradiation of an ethanol glass containing TPA at 77K does not produce an infrared absorption but produces peaks at 440 and 410nm in addition to the trapped-electron peak at 540nm. The peaks at 440 and 410nm are attributed to TPA − because absorbance at these peaks increases with increase in TPA concentration and that at 540nm decreases. The totality of the results for alcohol and 3-MP glasses suggests that e TPA − is an electron in a trap similar to that of e 3MP − but modified by the presence of a TPA molecule whose positive nitrogen end is oriented toward the electron.

Capture of the trapped electron in alcohol glasses

Scavenging of the presolvated electron was studied. In many matrices, the secondary electron is stabilized in shallow traps at first, and then it becomes solvated to deepen the potential well. Because the tunneling rate depends strongly on the height of the potential, scavenging by tunneling from the presolvated state possibly overcomes the tunneling from the solvated state even if the lifetime of the presolvated state is very short. Scavengers (benzene, fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, o-chlorotoluene, o- bromotoluene, and o-dichlorobenzene) were added to alcohols (methanol, ethanol, 1- propanol, and 2-propanol) and were cooled rapidly to make clear glasses. These glasses were irradiated by $gamma$ rays at 77$sup 0$K with the dose of about 0.2 Mrad. The yield of the solvated electron was estimated from the optical density of the wavelength of the peak of the absorption spectrum. For every scavenger, the efficiencies in the 1-propanol glasses are larger than those in the ethanol glass. Solvation times and tunneling radii were calculated. (JGB)

Trapped electrons studied through stimulated neutralization luminescence

The optically induced or ''stimulated'' neutralization luminescence (SL) following $gamma$ irradiation of rigid matrices can provide two types of information: (1) the emission spectrum characterizes the neutralization process, i.e., the neutralized cation or one of its dissociation fragments; (2) the excitation spectrum gives information on the nature and depths of the electron traps and occasionally on the trapped electrons e$sup -$/sub t/ spatial distribution. Examples of type 2 experiments performed at 77$sup 0$K on crystalline or glassy polar matrices are presented and discussed. The photodetrapping threshold values were found at 2.3 eV for ethanol glasses (lambda/ sub an/ 345 nm) and at 1.9 eV for crystalline H$sub 2$O or D$sub 2$O ices (lambda/ sub an/ 380 nm). No detrapping threshold appears in the SL spectra recorded from $gamma$-irradiated alkaline ices. (auth)