D.W. Werst

Radiation and photochemistry of onium salt acid generators in chemically amplified resists

The difference in photochemistry and radiation chemistry of sulfonium salt acid generator was investigated by product analysis and time resolved spectroscopic methods for chemically amplified resist application. After KrF excimer laser and electron beam irradiation of sulfonium salt, yields of decomposed products including acid were determined. The ultra fast in-cage reactions after laser irradiation were directly observed by the femtosecond laser flash photolysis method. Intermediates after electron beam irradiation were observed by nanosecond electron beam pulse radiolysis. From both the product analysis and time resolved spectroscopic methods, the contribution of each reaction pathway to acid generation was determined.

Self-exchange reactions of radical anions in n-hexane

Abstract The formation and reactions of radical anions in n-hexane at 190 K were investigated by pulse radiolysis and time-resolved fluorescence-detected magnetic resonance (FDMR). Electron attachment was found to occur for compounds with gas-phase electron affinities (EA) more positive than −1.1 ± 0.1 eV. The FDMR concentration and time dependence are interpreted as evidence for self-exchange electron-transfer reactions, indicating that formation of dimer radical anions is not prevalent for the range of molecules studied. FDMR detection of radical anions is mainly restricted to electron acceptors with EA less than approximately 0.5 eV.

Solvent effects in nonpolar solvents : radical anion reactions

Abstract Dimer radical anions, formed by anion—molecule reactions between octafluoronaphthalene and 1,2,4,5-tetrafluorobenzene and their respective radical anions, are observed in n-hexane solvent. The radical anions are characterized by their EPR spectra obtained by the time-resolved fluorescence-detected magnetic resonance technique. In toluene solvent the dimer anions are not formed. Rapid electron-exchange reactions occur instead in at least one case. Possible reasons why the solvent affects the anion reaction mechanism are discussed.

Olefin radical cations in pulse radiolysis of hydrocarbons.time-resolved fluorescence-detected magnetic resonance

Abstract Olefin radical cations are characterized by time-resolved fluorescence-detected magnetic resonance (FDMR) in pulse radiolysis of saturated hydrocarbons. Studies of both neat and mixed saturated hydrocarbon fluids by FDMR at low temperature(to≈ 100°C) suggest that olefin cations originate in the fragmentation of (vibrationally) excited (parent) saturated hydrocarboncations.

Radiation chemical studies in zeolites : radical cations and zeolite catalysis.

The constrained spaces within zeolites offer unique opportunities for chemical reaction control of very reactive intermediates. Here we review studies which illustrate the use of EPR detection of paramagnetic species following radiolysis of guest molecules in zeolites to gain new insights into reactions of organic radical cations. The radiolysis/EPR technique is also a valuable method to study catalytic transformations on acidic zeolites. In essence, radiolysis is used to spin label products of catalysis in order that they may be detected and identified by EPR. Several examples are presented to show that application at low temperatures makes the radiolysis/EPR method a promising new in situ spectroscopy for elucidating mechanisms in zeolite catalysis.

Quadricyclane and norbornadiene radical cations in silicalite: comparison with freon matrices☆

Abstract The radical cation of nonbornadiene is produced by γ radiolysis of nonbornadiene or quadricyclane in silicalite at 77 K. The bicyclo[3.2.0]hepta-2,6-diene radical cation and the bicyclo[2.2.1]hepta-2,5-diene-7-yl radical are observed at higher temperatures. The same radical cation chemistry was recently examined by EPR in freon matrices, and differences with this EPR study in zeolites are discussed. Some zeolite sites must be able to stabilize higher electronic states of radical cations, enabling otherwise photochemical processes to be thermally accessible in zeolites.

Elimination and ion—molecule reactions of hexamethylethane and trimethylbutane radical cations in ZSM-5

Abstract Hexamethylethane (HME) and trimethylbutane (TMB) radical cations produced in ZSM-5 zeolite by γ radiolysis undergo an elimination process followed by an ion—molecule reaction. The tetramethylethylen radical cation intermediate formed by CH 4 elimination from TMB + is observed directly in the temperature range 120–200 K. The deprotonation product, (CH 3 ) 3 CC (CH 3 ) 2 , of the cation—molecule reaction is observed for temperatures > 200 K. The isobutene radical cation formed by elimination of C 4 H 10 from HME +. is not observed-presumably because of rapid ion—molecule reaction to form the 2-methylallyl radical, which is observed.

Trap-to-trap hole transfer studied by radiolysis/EPR. Radical cations in freon and zeolite matrices

Abstract Electron paramagnetic resonance (EPR) spectroscopy was used to assess the positive charge distribution in irradiated solid samples containing mixtures of donor molecules. The relative trap populations were determined from the EPR intensities of the respective radical cations of the olefinic donors. The occurrence of trap-to-trap hole transfer was examined as a function of the donor pair, donor concentration, and matrix. Three matrices were studied: CF 3 CCl 3 , CFCl 3 , and ZSM5 zeolite. The concentration dependence of the final charge distributions in some cases reflected the occurrence of resonant charge transfer. Surprising differences between CF 3 CCl 3 and CFCl 3 are explained by differences in matrix chemistry. The radiolysis/EPR technique applied to double-loaded zeolites serves as a method of probing the intracrystalline adsorption distributions and mobilities of guest species in zeolites.

H atom diffusion and CIDEP in room temperature fused silica

Abstract We report the observation of H atom CIDEP in electron-irradiated a-SiO2:OH glass at room temperature. Analysis of the signals implies that atomic hydrogen diffuses several orders of magnitude faster than helium in fused silica.

Radical formation in the pulse radiolysis of liquid cyclohexane: Time-resolved EPR-scavenging study

Abstract The relative yields of cyclohexyl radical in pulse-irradiated liquid cyclohexane and cyclohexane solutions containing negative (CO2) and positive charge scavengers (cis- and trans-decalin) are measured via time-resolved EPR. Charge scavenging has a negligible effect on radical production. A mechanism of alkyl radical formation is suggested based on fragmentation of vibrationally excited cyclohexane radical cations.