Optical study of electrons and positive ions in pulse-irradiated liquid 3-methyloctane at low temperatures

Abstract

HUGH A. GILLIS, NOR MA^ V. KLASSEN, and ROBERT J. WOODS. Can. J. Chem. 55,2022Chem. 55, (1977. The spectrum of pulse-irradiated liquid 3-methyloctane at 127 K has maxima around 625 and 2100 nm. The latter is well-known as being due to the solvated electron (e,-). The former is attrib~~ted to a positive ion because it is eliminated by the addition of triethylamine, but remains in solutions of electron scavengers, and is very similar to bands observed earlier by Louwrier and Hamill in glassy solutions at 77 K of higher hydrocarbons in CCI, or COzbubbled 3-methylpentane. At temperatures of 127 K and less the initial decay rate of e,-is greatly decreased by the addition of -6 mol% triethylamine. The result is interpreted as indicating that at low temperatures the mobility of the initial hydrocarbon positive ion is much greater than that of either e,-or the positive ion in triethylamine solutions, and therefore the initial hydrocarbon positive ion must be the parent radical cation which moves by resonance charge transfer. As the temperature of pure 3-nlethyloctane is raised from 103 to 153 K, the initial G E , ,~~ decreases by about 3 0 x while initial G E~~, ,~ almost doubles; because of these and other observations it is tentatively suggested that a second solvated electron is also produced. Chern. 55.2022Chern. 55. (1977. Le spectre du methyl-3 octane liquide irradie par pulsation a 127 K a deux maxima autour de 625 et 2100 nm. On sait que le dernier maximum est dCi aux electrons solvates (e,-). Le premier est attribue a union positif parce qu'il est elimine par l'addition de triethylamine mais demeure dans des solutions de piegeurs d'electron et est trts semblable i des bandes qui ont Cte observees antirieurement par Louwrier et Hamill dans des solutions d'hydrocarbures de poids molCculaires plus eleves dissous dans des verres de CCI, a 77 K ou de methyl-3 pentane dans -1equel on a fait barbotter du CO,. A des temperatures de 127 K ou moins, le taux de dkconlposition initial de e,-diminue rapidement par addition -6 m o l z de triethylamine. On interprete des risultats comme indiquant qu'a basse temperature la mobilite de I'ion positif de I'hydrocarbure initial est beaucoup plus grande que celle de soit e,-ou I'ion positif dans des solutions de triithylamine et qu'ainsi l'ion positif de I'hydrocarbure initial doit @tre le cation radical parent qui se deplace par transfert de charge en resonance. A mesure que I'on augmente la temperature du methyl-3 octane de 103 a 153 K, le G~650 initial dirninue par environ 30% alors que le G E~,~~ initial double pratiquement; a cause de ces observations et d'autres, on suggere d'une f a~o n non definitive qu'il y a aussi production d'une seconde espece d'electron solvate.[Traduit par le journal]

Pulse radiolysis of hydrocarbon glasses at 6 and 77 K

“…3-Methyloctane. 3MO is probably the hardest of the glasses studied here with a viscosity of 1031 P at 77 K.10 It was of particular interest because of a previous report of a positive ion (RH+), with a Xmax of 625 nm, in liquid 3MO at 127 K. 6 From Figure 1 it can be seen that the positive ion is a more prominent feature in the glassy matrix than in the liquid. We find Xmax ~2000 nm for ef at both 6 and 77 K. The ratio Gemax>6K/GemaXi77K = 0.93 at 2000 nm and ~1.0 at 625 nm.…”

“…A value of Ge(SCN)2' = 2.2 X 104 molecules (100 eV)'1 M'1 cm'1 at 475 nm was used. Corrections were applied for the difference between the electron densities of the hydrocarbon glasses at 77 K and the dosimeter solution but it was assumed that the hydrocarbon densities at 6 a Ge values taken at the spectral maximum, 100 ns after the start of a 40-ns pulse. b Data taken from Kimura, Bremer, and Willard.1 c Comparisons of Ge73K to Ge77K were made at 1800 nm and assumed to be the same at the spectral maximum.…”

“…A cation (Xmax 625 nm) which decayed in several microseconds has been reported in pulse irradiated 3methyloctane liquid at 127 K. 6 We have studied this cation in 3-methyloctane glass at both 6 and 77 K.…”

“…The latter explanation seems to be borne out by the present work. We have measured the initial (100 ns) spectra of six hydrocarbon glasses following pulse radiolysis at 6 and 77 K and compared the initial Gemax(et") at 6 and 77 K to the yields reported for longer times.1 Electron tunneling in hydrocarbon glasses is discussed, with particular reference to the isothermal luminescence (ITL) results of Kieffer, Meyer, and Rigaut. 5 We conclude that the evidence favors temperature-dependent tunneling in hydrocarbon glasses.…”

Pulse Radiolytic Investigation of the Radiation‐Induced Cationic Primary Processes in Carbon Tetrachloride

“…In contrast to CCl;' and [CCl: ... C1-] this absorption is quenched by osygen and, therefore, it is concluded that it is a radical species. A comparison of the spectrum with results obtained in acidic sodium chloride solution 1211 shows that the transient might be the Cl; produced according to reaction (7).…”