@article {1551,
	title = {Slowing-down times and stopping powers for similar to 2-MeV mu(+) in low-pressure gases},
	journal = {Physical Review A},
	volume = {74},
	number = {4},
	year = {2006},
	note = {ISI Document Delivery No.: 101EXTimes Cited: 3Cited Reference Count: 86Senba, Masayoshi Arseneau, Donald J. Pan, James J. Fleming, Donald G.},
	month = {Oct},
	pages = {17},
	type = {Article},
	abstract = {The times taken by positive muons (mu(+)) to slow down from initial energies in the range similar to 3 to 1 MeV, to the energy of the last muonium formation, approximate to 10 eV, at the end of cyclic charge exchange, have been measured in the pure gases H-2, N-2, Ar, and in the gas mixtures Ar-He, Ar-Ne, Ar-CF4, H-2-He, and H-2-SF6, by the muon spin rotation (mu SR) technique. At 1 atm pressure, these slowing-down times, tau(SD), in Ar and N-2, vary from similar to 14 ns at the highest initial energies of 2.8 MeV to 6.5 ns at 1.6 MeV, with much longer times, similar to 34 ns, seen at this energy in H-2. Similar variations are seen in the gas mixtures, depending also on the total charge and nature of the mixture and consistent with well-established (Bragg) additivity rules. The times tau(SD) could also be used to determine the stopping powers, dE/dx, of the positive muon in N-2, Ar, and H-2, at kinetic energies near 2 MeV. The results demonstrate that the mu(+) and proton have the same stopping power at the same projectile velocity, as expected from the historic Bethe-Bloch formula, but not previously shown experimentally to our knowledge for the muon in gases at these energies. The energy of the first neutralization collision forming muonium (hydrogen), which initiates a series of charge-exchanging collisions, is also calculated for He, Ne, and Ar. The formalism necessary to describe the stopping power and moderation times, for either muon or proton, in three energy regimes-the Bethe-Bloch, cyclic charge exchange, and thermalization regimes-is developed and discussed in comparison with the experimental measurements reported here, and elsewhere. The slowing-down times through the first two regimes are controlled by the relevant ionization and charge-exchange cross sections, whereas the final thermalization regime is most sensitive to the forwardness of the elastic scattering cross sections. In this regime the slowing-down times (to kT) at nominal pressures are expected to be less than or similar to 100 ns.},
	keywords = {ALPHA-PARTICLES, BINARY THEORY, CHARGE-EXCHANGE, COMPETING PROCESSES, CROSS-SECTIONS, ELECTRON-SPIN EXCHANGE, HYDROGEN-ATOMS, MUONIUM-FORMATION, POSITIVE MUONS, RADIATION-CHEMISTRY},
	isbn = {1050-2947},
	url = {<Go to ISI>://000241723100090},
	author = {Senba, M. and Arseneau, D. J. and Pan, J. J. and Fleming, Donald G.}
}
@article {4135,
	title = {Fast muonium reactions in solution: An electron spin exchange interaction with Cr(NCS)(6)(3-) in water and reaction with iodine in organic solvents},
	journal = {Journal of Physical Chemistry A},
	volume = {101},
	number = {26},
	year = {1997},
	note = {ISI Document Delivery No.: XG935Times Cited: 3Cited Reference Count: 34},
	month = {Jun},
	pages = {4741-4744},
	type = {Article},
	abstract = {Two reactions of muonium atoms close to the diffusion-controlled limit were analyzed as a function of solute size and solvent viscosity. With Cr(NCS)(6)(3-) as solute in water, the reaction is an electron spin-conversion process, and the observed rate is taken to be half of the actual encounter rate, because of the quantum mechanical statistical factor and the occurrence of multiple collisions due to the solvent cage effect. The encounter rate deduced is 6.2 x 10(10) M-1 s(-1), which implies a large cross section for the Cr complex. In a second series of experiments, the rate of reaction of muonium with I-2 was compared in water, methanol and n-heptane. The bimolecular rate constants determined are (1.7 +/- 0.3), (7.0 +/- 1.2), and (57 +/- 22) x 10(10) M-1 s(-1), respectively, in these three solvents. This similar to 30-fold change in rate is not matched by the change in the inverse of the solvents{\textquoteright} viscosities, which changed overall by a factor of only 2.4. It looks as if quantum tunneling dominates over classical diffusion in less polar media where muonium is unencumbered by solvent clathration.},
	keywords = {AQUEOUS-SOLUTION, COMPLEXES, HYDROGEN-ATOMS, O-2, POSITRONIUM, radicals, relaxation, ROTATION},
	isbn = {1089-5639},
	url = {<Go to ISI>://A1997XG93500012},
	author = {Stadlbauer, J. M. and Venkateswaran, K. and Porter, G. B. and Walker, D. C.}
}
@article {4096,
	title = {Reaction kinetics of muonium with N2O in the gas phase},
	journal = {Journal of Physical Chemistry A},
	volume = {101},
	number = {45},
	year = {1997},
	note = {ISI Document Delivery No.: YF251Times Cited: 6Cited Reference Count: 64},
	month = {Nov},
	pages = {8470-8479},
	type = {Article},
	abstract = {The thermal reaction Mu + N2O has been studied by the muon spin rotation (mu SR) technique at temperatures from 303 to 593 K and pressures up to 60 atm. The overall reaction rate coefficient depends on the N2O pressure quadratically in pure N2O and is proportional to both the N2O partial pressure and the total pressure in mixtures, confirming the theoretical prediction of Diau and Lin that the analogous H atom reaction proceeds through two channels in this temperature range, forming different products, MuN(2)O and MuO + N-2. The measured total rate coefficients are much larger than those reported by Marshall et al. for H(D) + N2O, indicating a dramatic kinetic isotope effect, which is mainly due to the enhanced quantum tunneling of the ultralight Mu atom. Even at room temperature (and low pressure), k(Mu)/k(H) approximate to 120, the largest yet seen in comparisons of gas-phase Mu and H reactivity at such relatively high temperatures. The addition reaction forming MuN(2)O (and by implication, HN2O) contributes significantly to the total reaction rate at higher pressures but with the thermal rate coefficient remaining in the termolecular regime even at the highest pressures measured.},
	keywords = {ADDITION-REACTIONS, CHARGE-EXCHANGE, CHEMICAL-REACTION, H-ATOMS, HIGH-TEMPERATURE PHOTOCHEMISTRY, HYDROGEN-ATOMS, radicals, RATE CONSTANTS, SHOCK-TUBE, SPIN RELAXATION},
	isbn = {1089-5639},
	url = {<Go to ISI>://A1997YF25100014},
	author = {Pan, J. J. and Arseneau, D. J. and Senba, M. and Shelly, M. and Fleming, Donald G.}
}
@article {3822,
	title = {Micelle-induced change of mechanism in the reaction of muonium with acetone},
	journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie},
	volume = {74},
	number = {11},
	year = {1996},
	note = {ISI Document Delivery No.: WC124Times Cited: 1Cited Reference Count: 25},
	month = {Nov},
	pages = {1945-1951},
	type = {Article},
	abstract = {Muonium atoms add to the O atom of the carbonyl group of acetone to give the muonated free radical (CH3)(2)C-O-Mu when the reaction takes place in water or hydrocarbons, but not when the acetone is localized in micelles. Micelles have no effect on the formation of muonated cyclohexadienyl radicals when muonium reacts with benzene under similar conditions. The addition reaction with acetone appears to have been subsumed by a faster alternative reaction in the micellar environment. Evidence is presented for this interpretation rather than for an inhibition of the radical or for a shift in the muon level-crossing resonance spectrum with hydrogen (muonium) bonding, though major shifts are seen for the spectrum of this radical in pure solvents of widely different dielectric constant. It is suggested that muonium{\textquoteright}s {\textquoteright}{\textquoteright}abstraction{\textquoteright}{\textquoteright} reaction takes over in micelles because significant micelle-induced enhancement effects were previously observed in that type of reaction. The data are consistent with a I ate constant for the abstraction reaction of muonium with acetone in micelles of >6 x 10(8) M(-1) s(-1).},
	keywords = {AQUEOUS-SOLUTIONS, H/Mu abstraction, H/Mu-addition, HYDROGEN-ATOMS, kinetic isotope effects, LEVEL-CROSSING-RESONANCE, micelle enhancement, muonium, radical formation, SOLUTES, SPECTROSCOPY, WATER},
	isbn = {0008-4042},
	url = {<Go to ISI>://A1996WC12400008},
	author = {Stadlbauer, J. M. and Venkateswaran, K. and Gillis, H. A. and Porter, G. B. and Walker, D. C.}
}
@article {2889,
	title = {MUONIUM ATOM SPIN-EXCHANGE WITH ALKALI-METAL VAPORS - MU+CS},
	journal = {Physical Review A},
	volume = {48},
	number = {2},
	year = {1993},
	note = {ISI Document Delivery No.: LQ990Times Cited: 15Cited Reference Count: 77},
	month = {Aug},
	pages = {1218-1226},
	type = {Article},
	abstract = {The thermally averaged total electron spin-flip cross sections (sigma(SF)) for Mu-Cs have been measured in a 2 atm N2 moderator at 543, 566, and 643 K using the muon-spin-rotation technique. Within an overall experimental error of +/-15\%, the measured cross sections can be taken as temperature independent, sigma(SF)=39.7+/-6.0 X 10(-16) cm2, though there may be a trend to decreased values at the lower temperatures. This average value is considerably lower than either the early calculated results of Dalgarno and Rudge [Proc. R. Soc. London Ser. A 286, 519 (1965)] or the more recent ones of Cole and Olson [Phys. Rev. A 31, 2137 (1985)] for the corresponding H-Cs collisions, indicating a dramatic isotope effect.},
	keywords = {ADDITION-REACTIONS, COLLISIONS, CROSS-SECTIONS, ENERGIES, HYDROGEN-ATOMS, LOW-PRESSURE GASES, MU-SR, RATE CONSTANTS, relaxation, SCATTERING},
	isbn = {1050-2947},
	url = {<Go to ISI>://A1993LQ99000046},
	author = {Pan, J. J. and Senba, M. and Arseneau, D. J. and Kempton, J. R. and Fleming, Donald G. and Baer, S. and Gonzalez, A. C. and Snooks, R.}
}
@article {7041,
	title = {EPITHERMAL MUONIUM PROCESSES IN METHANE AND PROPANE GASES},
	journal = {Journal of Physical Chemistry},
	volume = {95},
	number = {19},
	year = {1991},
	note = {ISI Document Delivery No.: GG383Times Cited: 7Cited Reference Count: 90},
	month = {Sep},
	pages = {7338-7344},
	type = {Article},
	abstract = {Gas-phase mu-SR studies of dense methane up to 10 mol L-1 and of propane at low densities, up to 0.2 mol L-1, are reported. It is found that the diamagnetic polarization, P(D), increases in both gases with pressure, with a related decrease seen in the muonium polarization, P(Mu). The initial increase seen in P(D) at low densities is attributed to hot-atom (Mu*) abstraction and substitution reactions. Comparisons with both hot-tritium (T*) and epithermal H* reactions in the alkanes reveal substantial isotope effects. In the case of CH4, a continued increase in P(D) at higher densities is likely due to a proton-transfer reaction from the molecular ion CH4Mu+ in the radiolysis track, forming CH3Mu, rather than to hot-atom reactions. Extrapolation of the present trend with density gives agreement with the value of P(D) found in liquid CH4, indicating that the diamagnetic muon polarization in dense alkanes depends primarily on density rather than on temperature or phase.},
	keywords = {CHARGE-EXCHANGE, CHEMISTRY, HOT-ATOM REACTIONS, HYDROCARBONS, HYDROGEN-ATOMS, LIQUIDS, POSITRONIUM, REACTION PROBABILITIES, THRESHOLD ENERGY, time},
	isbn = {0022-3654},
	url = {<Go to ISI>://A1991GG38300043},
	author = {Kempton, J. R. and Arseneau, D. J. and Fleming, Donald G. and Senba, M. and Gonzalez, A. C. and Pan, J. J. and Tempelmann, A. and Garner, D. M.}
}
