Received; accepted 1 Visiting Astronomer, MMT Observatory. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution 2 Visiting Astronomer, Steward Observatory 2.3 m Telescope. ABSTRACTWe present spectra of Eris from the MMT 6.5 meter telescope and Red Channel Spectrograph (5700−9800Å; 5Å pix −1 ) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 meter telescope and Boller and Chivens spectrograph (7100−9400Å; 2Å pix −1 ) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane-nitrogen and methane-argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich (1983), and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ∼ 10% and ∼ 90% and Pluto's bulk methane and nitrogen abundances are ∼ 3% and ∼ 97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition ofPluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 µm band is seen in spectra of Pluto and Triton.

The flowing afterglow technique has been used to study the reactions of H3+ with a number of neutral reactants at thermal energies. Proton transfer was the only primary reaction observed with N2, CO, CO2, N2O, NO, CH4, C2H2, H2O, and NH3. Both proton transfer and dissociative charge transfer were observed with C2H4 and C2H6, while dissociative charge transfer is the exclusive primary process with NO2. Secondary reactions were observed with NO, C2H6, C2H4, and C2H2. Cluster ions were formed between NO+ and NO2 and H2O, between H3O+ and H2O, CO2, and CO, and between NH4+ and NH3 and H2O. Proton transfer was also observed between HN2+ and CO2, N2O, CH4, and H2O, and between HO2+ and H2 and N2. Rate constants were obtained for these reactions and are discussed. Limits could be placed on the proton affinity (P.A.) of H2 from the failure to observe rapid proton transfer to O2 and the observation of proton transfer to N2. These indicate 4.2 < P.A. (H2)< 4.7 eV with a recommended value of 4.4 eV. The technique can be used to measure relative proton affinities of gases.

The flowing afterglow technique has been used to study the electron detachment reactions OZ(lAg) + 02--f 2 0 2 + e and 02('Ag) + 0--f O3 + e The rates of these reactions are sufficiently fast to make them important processes in D region ionospheric chemistry.

The solvatochromic dye betaine-30 is thermochromic as well, due to the temperature dependence of solvent polarity, which strongly influences the wavelength of the visible absorption band. We report an analysis of the temperature-dependent absorption spectrum of betaine-30 in CH 3 CN, incorporating the internal-mode displacements determined from the resonance Raman profiles at room temperature. The temperature-dependent solvent reorganization energy λ solv associated with the visible transition of betaine-30 influences the width and position of the absorption spectrum and is relevant to theories for the rate of return electron transfer. We have previously determined λ solv for betaine-30 in acetonitrile and deuterated acetonitrile from analysis of the room-temperature absorption and resonance Raman profiles using time-dependent spectroscopy theory. In this work, we present a revised set of normal-mode displacements, including the contribution from a torsional mode of betaine-30 at 133 cm -1 , obtained from an analysis of the room-temperature Raman profiles in CH 3 -CN and CD 3 CN. These displacements are then kept fixed, and the temperature-dependent absorption spectrum of betaine-30 in acetonitrile is modeled to obtain the solvent reorganization energy, 0-0 energy, and transition moment as a function of temperature. The solvent reorganization energy λ solv is found to decrease with increasing temperature, consistent with decreasing solvent polarity but opposite to the prediction of dielectric continuum theory. In contrast to our previous analysis, the nonlinear solvent response is included in the model, and the amplitude of the solvent response is found to be smaller in the excited than the ground electronic state, due to the decrease in solute dipole moment in the excited electronic state.

Resonance Raman profiles for 14 vibrational modes of betaine-30 in ethanol at room temperature were measured at wavelengths within the first charge-transfer absorption band. The absorption spectrum and resonance Raman profiles were analyzed using time-dependent theory and a Brownian oscillator model modified to account for nonlinear solvent response; i.e., dependence of the solvent reorganization energy on the electronic state of the solute. As in our previous study of betaine-30 in acetonitrile, the solvent reorganization energy for the excited electronic state, determined from resonance Raman spectroscopy, was found to be smaller than that for the ground electronic state, determined from the absorption spectrum. The mode-dependent internal reorganization energies of betaine-30 in ethanol were found to be slightly larger than those of betaine-30 in acetonitrile. Temperature-dependent solvent reorganization energies for the ground electronic state were determined from analysis of the absorption line shape from 279 to 332 K and were found to decrease with increasing temperature. The influence of hydrogen bonding on the solvent and internal reorganization energy of betaine-30 is considered, and the physical basis for nonlinear solvent response is discussed.