@article {4897, title = {Measurements of Mu+NO termolecular kinetics up to 520 bar: isotope effects and the Troe theory}, journal = {Physical Chemistry Chemical Physics}, volume = {2}, number = {4}, year = {2000}, note = {ISI Document Delivery No.: 281JDTimes Cited: 3Cited Reference Count: 58}, pages = {621-629}, type = {Article}, abstract = {The recombination reaction Mu + NO + MMuNO + M (M = He, N-2, CH4) has been studied by the muon spin relaxation/rotation (mu SR) technique up to 520 bar at room temperature. The reaction remains in the low pressure regime throughout. The measured termolecular addition rate constant in N-2, 8.8 +/- 0.3 x 10(-33) cm(6) s(-1), is essentially the same as that found in our earlier study at pressures below 60 bar [J. J. Pan et al., J. Phys. Chem., 1995, 99, 17160]. It is somewhat smaller in He, 7.7 +/- 1.0 x 10(-33), but larger in CH4, 12.8 +/- 2.0 x 10(-33). The Mu + NO reaction is about five times slower than the corresponding H + NO reaction. The strong collision limits of the rate constants for three H-isotopes (Mu, H, D) reacting with NO have been estimated with Troe{\textquoteright}s formalism for unimolecular dissociation in the low pressure regime, based on the ab initio potential energy surface of Guadagnini et al. [J. Chem. Phys., 1995, 102, 774]. The Troe calculations give less than satisfactory agreement with experiment with the corresponding weak collision factor, beta(c), higher than expected by a factor of similar to 2 for H + NO. The calculated kinetic isotope effect in the strong collision limit for Mu/H is weaker than the measured effect by a factor of two giving an apparent large isotope effect in this factor, beta(c)(Mu) approximate to 1/2,beta(o)(H), possibly due to mode specific collisional stabilization.}, keywords = {COLLISIONAL ENERGY-TRANSFER, DISSOCIATION, ELECTRON-SPIN EXCHANGE, GAS-PHASE, HIGH-PRESSURES, HNO, muonium, RATE CONSTANTS, relaxation, THERMAL UNIMOLECULAR REACTIONS}, isbn = {1463-9076}, url = {://000085154400025}, author = {Pan, J. J. and Arseneau, D. J. and Senba, M. and Fleming, Donald G. and Himmer, U. and Suzuki, Y.} } @article {4565, title = {Kinetic isotope effect in the gas-phase reaction of muonium with molecular oxygen}, journal = {Journal of Physical Chemistry A}, volume = {103}, number = {13}, year = {1999}, note = {ISI Document Delivery No.: 184KQTimes Cited: 13Cited Reference Count: 101}, month = {Apr}, pages = {2076-2087}, type = {Review}, abstract = {The rate constant of the gas-phase addition reaction of the light hydrogen isotope muonium to molecular oxygen, Mn + O-2 {\textendash}> MuO(2), was measured over a range of temperatures from 115 to 463 K at a pressure of 2 bar and from 16 to 301 bar at room temperature, using N-2 as the moderator gas. The reaction remains in the termolecular regime over the entire pressure range. At room temperature, the average low-pressure limiting rate constant is k(ch)(0)(Mu) = (8.0 +/- 2.1) x 10(-33) cm(6) s(-1), a factor of almost 7 below the corresponding rate constant for the H + O-2 addition reaction, k(ch)(0)(H). In contrast to k(ch)(0)(H), which exhibits a clear negative temperature dependence, k(ch)(0)(MU) is essentially temperature independent. At room temperature, the kinetic isotope effect (KIE) is strongly pressure (density) dependent and is reversed at pressures near 300 bar. The kinetics are analyzed based on the statistical adiabatic channel model of Tree using a Morse potential, which works well in reproducing the overall KIE. The major factors governing the isotope effect are differences in the moment of inertia and density of vibrational states of the addition complex.}, keywords = {ABSOLUTE RATE, CHARACTERIZATION, COLLISION RATE CONSTANTS, CONSTANTS, ELECTRON-SPIN-EXCHANGE, LOW-PRESSURES, POTENTIAL-ENERGY SURFACE, RATE COEFFICIENTS, THEORETICAL, THERMAL UNIMOLECULAR REACTIONS, TRAJECTORY CALCULATIONS, TRANSITION-STATE THEORY}, isbn = {1089-5639}, url = {://000079611700020}, author = {Himmer, U. and Dilger, H. and Roduner, E. and Pan, J. J. and Arseneau, D. J. and Fleming, Donald G. and Senba, M.} }