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The surface chemistry of ethyl iodide over a Pd(100) surface has been studied at 90-450 K with the aim of generating C 2 H 5 species. The methods used included Auger electron spectroscopy (AES), photoelectron spectroscopy (XPS and UPS), temperature-programmed desorption (TPD), and work function measurements. Ethyl iodide adsorbs molecularly on a Pd(100) surface at 90 K, and this adsorption is followed by a multilayer formation at high exposures. Adsorption of C 2 H 5 I is characterized by a work function decrease (2.00 eV at monolayer), indicating that adsorbed C 2 H 5 I has a large, positive outward dipole moment. The thermal dissociation

The surface chemistry of ethyl iodide was studied by using thermal programmed desorption (TPD) spectroscopy. Partially deuterated ethyl iodide molecules (CD{sub 3}CH{sub 2}I and CH{sub 3}CD{sub 2}I) were used to determine the mechanism for the reactivity of ethyl groups on the surface. Breaking of the C-I bond on Pt(111) at temperatures below 200 K results in the formation of ethyl moieities. The thermal desorption experiments suggest that those ethyl groups dehydrogenate immediately after being formed to yield ethylene. Partial deuterium labeling on the ethyl moeities was used to demonstrate that such reaction occurs by elimination of a hydrogen atom in the {beta} position (the farthest from the surface). Chemisorbed ethylene rehydrogenates at higher temperatures to form ethyl groups again, which then either hydrogenate immediately to form ethane or dehydrogenate back to ethylene (a mechanism responsible for H-D exchange). Additional experiments in which hydrogen or deuterium was coadsorbed with the ethyl iodide also help in elucidating the mechanism for the reactions involved. Finally, the authors used the kinetic information obtained with TPD to calculate the energetics of the surface steps studies here.

The external heavy atom induced phosphorescence of C{sub 60} and C{sub 70} is obtained at 77 K in a glass containing ethyl iodide and gives 12 690 {plus_minus} 30 cm{sup {minus}1} as a precise lower limit for the energy of triplet C{sub 60}. Triplet lifetime measurements show that the heavy atom effect is relatively much greater on the S{sub 1} {yields} T{sub 1} than on the T{sub 1} {yields} S{sub 0} radiationless transitions, as expected from the smaller Franck-Condon constraints in the former process. 26 refs., 2 figs.

The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.

The fluorescence decay of trans (2-anthryl)ethylenes containing phenyl, 2-naphthyl, and 2-thienyl groups as the second substituent is biexponential. The decay profiles in benzene are analyzable in terms of two lifetimes in the ranges 6-11 and 17-30 ns, respectively. The complex decay behavior as well as the observation of excitation wavelength dependence of fluorescence spectra, quantum yields, exciplex emission maxima, and fluorescence quenching constants (with oxygen, ethyl iodide (EtI), and N,N-dimethylaniline (DMA) as quenchers) is attributed to the existence of quasi-energetic rotamers in solutions of (2-anthryl)ethylenes. Exciplex lifetimes and transient absorption spectra of radical anions obtained by nanosecond laser flash photolysis in the presence of N,N-dimethylaniline are also presented. 17 references, 6 figures, 6 tables.

This paper summarizes some of the data in the literature on the effects of phase on chemical reactions induced in organic systems by light, ionizing radiation and nuclear transformations. It also presents new data which show that: (1) the ratio of HI to I/sub 2/ produced in the radiolysis of pure isopropyl iodide with Co/sup 60/ gamma -rays is about tenfold higher in the solid phase at --190 deg than in the liquid at room temperature; (2) the yield of iodine from the radiolysis of isopropyl iodide in either the liquid or solid is dependent on the past history of irradiation of the sample in the other phase; (3) when the spectrum of ethyl iodide glass at --190 deg is examined after exposure of the solid to 2537 A. light, little or no change is observed as a result of the irradiation, but when the glass is then melted amd immediately refrozen, an absorption peak appears at 3700 A.; a similar effect is caused by the self-irradiation of tritiated ethyl iodide glass; (4) the ratio of HI to I/ sub 2/ produced by the photolysis of ethyl iodide is approximately ten-fold higher in the glass at --190 deg than inmore » the liquid at room temperature. (auth)« less

Iodine production induced by gamma radiolysis was measured for solutions of methyl iodide in cyclohexane and ethyl iodide in cyclohexane, over the concentration range 0--95% cyclohexane by volume. In each case the addition of cyclohexane caused a smooth decrease in iodine production from the alkyl iodide, but net iodine production persisted until at least 93 electron% cyclohexane was added. The observations are discussed in terms of a previously proposed mechanism.

The ratio k/sub disproportionation//k/sub combination/ (k/sub d//k/sub c/) was determined for ethyl radicals in aqueous solution. Radicals were generated by several independent photochemical and thermal methods: photolysis of (NH/sub 3/)/sub 5/CoO/sub 2/CC/sub 2/H/sub 5//sup 2 +/; photolysis of (C/sub 2/H/sub 5/)/sub 2/CO; reduction of ethyl iodide by photochemically generated (CH/sub 3/)/sub 2/CO/sup -/.; reduction of C/sub 2/H/sub 5/C(CH/sub 3/)/sub 2/OOH by V(H/sub 2/O)/sub 6//sup 2 +/ and by Fe(H/sub 2/O)/sub 6//sup 2 +/. The agreement between different methods is good, yielding k/sub d//k/sub c/ = 0.35 +/- 0.04. The effect of solvent polarity and internal pressure on k/sub d//k/sub c/ is discussed. 21 references, 2 figures, 1 table.