Exploring the correlation between network structure and electron binding energy in the (H2 O) 7- cluster through isomer-photoselected vibrational predissociation spectroscopy and ab initio calculations: Addressing complexity beyond types I-III

We report a combined photoelectron and vibrational spectroscopy study of the (H2 O) 7- cluster anions in order to correlate structural changes with the observed differences in electron binding energies of the various isomers. Photoelectron spectra of the (H2 O) 7- Arm clusters are obtained over the range of m=0-10. These spectra reveal the formation of a new isomer (I′) for m<5, the electron binding energy of which is about 0.15 eV higher than that of the type I form previously reported to be the highest binding energy species [Coe, J. Chem. Phys. 92, 3980 (1990)]. Isomer-selective vibrational predissociation spectra are obtained using both the Ar dependence of the isomer distribution and photochemical depopulation of the more weakly (electron) binding isomers. The likely structures of the isomers at play are identified with the aid of electronic structure calculations, and the electron binding energies, as well as harmonic vibrational spectra, are calculated for 28 low-lying forms for comparison with the experimental results. The HOH bending spectrum of the low binding type II form is dominated by a band that is moderately redshifted relative to the bending origin of the bare water molecule. Calculations trace this feature primarily to the bending vibration localized on a water molecule in which a dangling H atom points toward the electron cloud. Both higher binding forms (I and I′) display the characteristic patterns in the bending and OH stretching regions signaling electron attachment primarily to a water molecule in an AA binding site, a persistent motif found in non-isomer-selective spectra of the clusters up to (H2 O) 50-. © 2008 American Institute of Physics

Infrared spectrum and structural assignment of the water trimer anion

The bending vibrational spectrum of the perdeutero isotopomer of the water trimer anion has been measured and compared with spectra calculated using the MP2, CCSD, and Becke3LYP electronic structure methods. Due to its low electron binding energy (≈150 meV), only the OD bending region of the IR spectrum of (D 2O) 3- is accessible experimentally, with electron ejection dominating at higher photon energies. The calculated spectrum of the isomer having three water molecules arranged in a chain agrees best with the experimental spectrum. In the chain isomer, the excess electron is bound to the terminal water monomer with two dangling OH groups. This is consistent with the electron binding mechanism established previously for the (H 2O) n- (n = 2, 4-6) anions. © 2005 American Chemical Society

Using the tracer flux ratio method with flight measurements to estimate dairy farm CH4 emissions in central California

Tracer flux ratio methodology was applied to airborne measurements to quantify methane (CH4) emissions from two dairy farms in central California during the summer. An aircraft flew around the perimeter of each farm measuring downwind enhancements of CH4 and a tracer species released from the ground at a known rate. Estimates of CH4 emission rates from this analysis were determined for whole sites and major sources within a site (animal housing and liquid manure lagoons). Whole-site CH4 flux rates for each farm, Dairy 1 (6108±821kgCH4dg-1, 95% confidence interval) and Dairy 2 (4018±456kgCH4dg-1, 95% confidence interval), closely resembled findings by established methods: ground-based tracer flux ratio and mass balance. Individual source emission rates indicate a greater fraction of the whole-site emissions come from liquid manure management than animal housing activity, similar to bottom-up estimates. Despite differences in altitude, we observed that the tracer release method gave consistent results when using ground or air platforms.

The vibrational predissociation spectra of the H <inf>5</inf>O <inf>2</inf>⁺·RG <inf>n</inf>(RG=Ar,Ne) clusters: Correlation of the solvent perturbations in the free OH and shared proton transitions of the Zundel ion

Predissociation spectra of the H5 O2+ ·R Gn (RG=Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm-1) and shared proton (850-1950 cm-1) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H5 O2+ [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H5 O2+ "Zundel" ion remains largely intact in H5 O2+ ·Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H5 O2+ ·Ar, and is dominated by two sharp transitions at 928 and 1047 cm-1, with a weaker feature at 1763 cm-1. The H5 O2+ · Arn, n=1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H5 O2+ rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H5 O2+. These results are consistent with assignment of the strong low-energy bands in the H5 O2+ ·Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm-1 band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules. © 2005 American Institute of Physics

HIGH RESOLUTION SPECTROSCOPY AND DYNAMICS: FROM JET COOLED RADICALS TO GAS-LIQUID INTERFACES

Author Institution: JILA, University of Colorado and National Institute of Standards and Technology, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0440; Los Gatos Research, 67 E. Evelyn Ave. Suite 3, Mountain View, CA 94041; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave Building 6-026, Cambridge, MA 02139This talk will attempt to reflect recent work in our group involving two quite different but complementary applications of high resolution molecular spectroscopy for detailed study of intramolecular as well as intermolecular dynamics in small molecules. The first is based on direct infrared absorption spectroscopy in a 100 KHz slit supersonic discharge, which provides a remarkably versatile and yet highly sensitive probe for study of important chemical transients such as open shell combustion species and molecular ions under jet cooled (10-20K), sub-Doppler conditions. For this talk will focus on gas phase spectroscopic results for a series of unsaturated hydrocarbon radical species (ethynyl, vinyl, and phenyl) reputed to be critical intermediates in soot formation. Secondly, we will discuss recent applications of high resolution IR and velocity map imaging spectroscopy toward quantum state resolved collision dynamics of jet cooled molecules from gas-room temperature ionic liquid (RTIL) and gas-self assembled monolayer (SAM) interfaces. Time permitting, we will also present new results on hyperthermal scattering of jet cooled NO radical from liquid Ga, which offer a novel window into non-adiabatic energy transfer and electron-hole pair dynamics at the gas-molten metal interface