@article {860,
	title = {Muonium formation as a probe of radiation chemistry in sub- and supercritical carbon dioxide},
	journal = {Journal of Physical Chemistry A},
	volume = {108},
	number = {52},
	year = {2004},
	note = {ISI Document Delivery No.: 882FPTimes Cited: 5Cited Reference Count: 97},
	month = {Dec},
	pages = {11613-11625},
	type = {Article},
	abstract = {Muonium (Mu = mu(+)e(-)), which can be considered a light isotope of the H atom, has been observed for the first time in supercritical CO2 (ScCo2). It is Unreactive on a time scale of a few microseconds and over a wide density range from well below to well above the CO2 critical density rho(c) = 0.47 g/cm(3). The fraction of muon polarization in muonium, P-Mu, does not vary significantly at low densities but changes quickly at the highest densities, approaching zero. This density dependence is reflected in a concomitant increase observed in the lost fraction of polarization, P-L, demonstrating that the dynamics of Mu formation and depolarization in ScCO2 is a direct probe of radiolysis effects in the terminal muon radiation track. In marked contrast to previous studies in hydrogen-containing solvents, C2H6 and H2O, over comparable density ranges, the diamagnetic fraction, P-D, was found to be almost independent of density in CO2, attributed to the formation of the stable solvated MuCO(2)(+) molecular ion in this hydrogen-free solvent. The differing density dependences of both the Mu and the diamagnetic fraction in Co-2, in comparison with the rather similar trends seen for both in C2H6 and H2O, supports previous claims of a significant role played by proton (muon) transfer reactions in the competing processes involved in Mu formation in hydrogen-containing solvents. In addition to this being the first report of radiolysis effects accompanying energetic positive muons stopping in ScCO2, it is the only report of end of track effects in this solvent, which has many applications in nuclear waste management and green chemistry. With a mass intermediate between that of the electron, which has provided most radiation-chemistry studies in ScCO2 to date, and the proton (or alpha-particle), implanted muons provide a unique data set, characteristic of higher LET radiation, that may be relevant to radiolysis effects induced in ScCO2 by alpha decay from heavy nuclei, for which there are no comparable studies.},
	keywords = {AQUEOUS-SOLUTIONS, CROSS-SECTIONS, EXCESS ELECTRON-TRANSPORT, GAS-PHASE, LIQUID WATER, MAGNETIC-RESONANCE, ORGANIC FREE-RADICALS, PRESSURE-DEPENDENCE, relaxation, SOLVENT ANIONS, SPIN},
	isbn = {1089-5639},
	url = {<Go to ISI>://000225924800018},
	author = {Ghandi, K. and Bridges, M. D. and Arseneau, D. J. and Fleming, Donald G.}
}
@article {3960,
	title = {Hyperfine coupling constants of muonium-substituted cyclohexadienyl radicals in the gas phase: C(6)H(6)Mu, C(6)D(6)Mu, C(6)F(6)Mu},
	journal = {Applied Magnetic Resonance},
	volume = {13},
	number = {1-2},
	year = {1997},
	note = {ISI Document Delivery No.: YE729Times Cited: 13Cited Reference Count: 33},
	pages = {181-194},
	type = {Article},
	abstract = {Muon spin rotation (mu SR) and avoided level crossing resonance (ALCR) have been used to determine the hyperfine coupling constants (hfcs) of the muonium-substituted cyclohexadienyl radicals C(6)H(6)Mu, C(6)D(6)Mu and C(6)F(6)Mu in the gas phase, at pressures similar to 1 and 15 atm and temperatures in the range 40-80 degrees C. Equivalent studies of polyatomic free radicals in gases, by electron spin resonance (ESR) spectroscopy, are generally not possible in this pressure range. The present gas phase results support the findings of earlier studies of cyclohexadienyl radicals in the condensed phase, by both mu SR and ESR. Minor but not insignificant (similar to 1\%) effects on the hfcs are observed, which can be qualitatively understood for such nonpolar media in terms of their differing polarizabilities. This is the first time that comparisons of this nature have been possible between different phases at the same temperatures. These mu SR/ALCR gas-phase results provide a valuable benchmark for computational studies on radicals, free from possible effects of solvent or matrix environments.},
	keywords = {ETHYL RADICALS, LEVEL-CROSSING SPECTROSCOPY, ORGANIC FREE-RADICALS, RESONANCE, SPECTRA, SPIN ROTATION},
	isbn = {0937-9347},
	url = {<Go to ISI>://A1997YE72900015},
	author = {Fleming, Donald G. and Arseneau, D. J. and Pan, J. J. and Shelley, M. Y. and Senba, M. and Percival, P. W.}
}
@article {3940,
	title = {Why ALC mu SR is superior for gas-phase radical spectroscopy},
	journal = {Hyperfine Interactions},
	volume = {106},
	number = {1-4},
	year = {1997},
	note = {ISI Document Delivery No.: XB055Times Cited: 9Cited Reference Count: 147th International Conference on Muon Spin Rotation, Relaxation, ResonanceAPR 15-19, 1996NIKKO, JAPANUniv Tokyo, Meson Sci Lab, Inst Phys \& Chem Res, Muon Sci Lab},
	pages = {137-142},
	type = {Proceedings Paper},
	abstract = {ALC mu SR spectra of the muonated ethyl and cyclohexadienyl radicals in the gas phase are reported. They have surprisingly narrow lines for a magnetic resonance type technique under conditions near ambient temperature and near 1 atmosphere pressure. The main reason for this behaviour is the dramatic reduction of electron spin relaxation in high magnetic fields.},
	keywords = {HYPERFINE CONSTANTS, ORGANIC FREE-RADICALS, SPECTRA, SPIN RELAXATION},
	isbn = {0304-3843},
	url = {<Go to ISI>://A1997XB05500019},
	author = {Dilger, H. and Roduner, E. and Stolmar, M. and Reid, I. D. and Fleming, Donald G. and Arseneau, D. J. and Pan, J. J. and Senba, M. and Shelley, M.}
}
@article {3664,
	title = {Spin relaxation of muonium-substituted ethyl radicals (MuCH(2)CH(2)) in the gas phase},
	journal = {Journal of Chemical Physics},
	volume = {105},
	number = {17},
	year = {1996},
	note = {ISI Document Delivery No.: VP288Times Cited: 20Cited Reference Count: 84},
	month = {Nov},
	pages = {7517-7535},
	type = {Article},
	abstract = {The spin relaxation of the muonium-substituted ethyl radical (MuCH(2)CH(2)) and its deuterated analog (MuCD(2)CD(2)) has been studied in the gas phase in both transverse and longitudinal magnetic fields spanning the range similar to 0.5-35 kG, over a pressure range from similar to 1-16 atm at ambient temperature. The Mu(13)CH(2)(13)CH(2) radical has also been investigated, at 2.7 atm. For comparison, some data is also reported for the MuCH(2)C(CH3)(2) (Mu-t-butyl) radical at a pressure of 2.6 atm. This experiment establishes the importance of the mu SR technique in studying spin relaxation phenomena of polyatomic radicals in the gas phase, where equivalent ESR data is sparse or nonexistent. Both T-1 (longitudinal) and T-2 (transverse) mu SR relaxation rates are reported and interpreted with a phenomenological model. Relaxation results from fluctuating terms in the spin Hamiltonian, inducing transitions between the eigenstates assumed from an isotropic hyperfine interaction. Low-field relaxation is primarily due to the electron, via both the nuclear hyperfine (S . A . I) and the spin rotation interactions (S . J), communicated to the muon via the isotropic muon-electron hyperfine interaction. At the highest fields, direct spin flips of the muon become important, due to fluctuations in the anisotropic part of the muon-electron hyperfine interaction. In the intermediate held region a muon-electron {\textquoteright}{\textquoteright}flip-flop{\textquoteright}{\textquoteright} relaxation mechanism dominates, due partly to the anisotropic hyperfine interaction and partly to modulation of the isotropic muon-electron hyperfine coupling. In the case of the T-2 rates, electron relaxation mechanisms dominate over a much wider field range than for the T-1 rates, and inhomogeneous line broadening also contributes. The fluctuations that induce both the T-1 and T-2 relaxation rates are described by a single correlation time, tau(c), inversely proportional to the pressure. An effective spin-reorientation cross section is deduced from this pressure dependence, sigma(J) similar to 100+/-20 Angstrom(2), for all topically substituted ethyl radicals. This is similar to the geometrical cross section, but about a factor of 4 larger than values of sigma(J) found for similar-sized diamagnetic molecules by gas phase NMR, primarily reflecting the longer range of the electron-induced intermolecular potential. (C) 1996 American Institute of Physics.},
	keywords = {ADDITION-REACTIONS, DYNAMICS, EXCHANGE, HYPERFINE COUPLING-CONSTANTS, INTERNAL-ROTATION, LATTICE RELAXATION, LEVEL-CROSSING, MAGNETIC-RESONANCE, MUONATED RADICALS, ORGANIC FREE-RADICALS, SPECTROSCOPY},
	isbn = {0021-9606},
	url = {<Go to ISI>://A1996VP28800027},
	author = {Fleming, Donald G. and Pan, J. J. and Senba, M. and Arseneau, D. J. and Kiefl, R. F. and Shelley, M. Y. and Cox, S. F. J. and Percival, P. W. and Brodovitch, J. C.}
}
