OVERTONE VIBRATIONAL SPECTROSCOPY AND DYNAMICS IN H2_2-H2_2O COMPLEXES: A COMBINED THEORETICAL AND EXPERIMENTAL STUDY

Author Institution: JILA, University of Colorado and National Institute of; Standards and Technology, Boulder, Colorado; CNRS-Universite de Bourgogne, Dijon, France; CNRS, Institut de Planetologie et d'Astrophysique de Grenoble, France; Radboud University, 6525 AJ Nijmegen, The NetherlandsH$_2$ is the most abundant molecule in the universe and also H$_2$O occurs in relatively high concentrations in various interstellar environments. Processes that occur through the interaction of these molecules may, for example, play a role in the mechanism producing the observed H$_2$O maser activity. Spectroscopic studies of the H$_2$-H$_2$O complex in different stable and metastable states will be reported in the accompanying talk; theoretical studies will be presented here. The latter involve calculations of the bound rovibrational levels of the complex with both monomers in their vibrational ground state, as well as of the metastable levels with H$_2$O in its OH stretch overtone state, on the appropriate \textit{ab initio} five-dimensional intermolecular potential surfaces. Also the line strengths of all the allowed transitions between these levels that may occur in combination with the $v_{\rm OH} = 2 \leftarrow 0$ overtone transition were computed, for all four ortho/para H$_2$ and ortho/para H$_2$O variants of the complex. The spectrum simulated with these data agrees very well with the measured spectrum and was used to assign this spectrum. In addition, the information obtained from the theory was useful to understand the observed predissociation dynamics of the complex

Ultrafast relaxation of photoexcited superfluid He nanodroplets

The relaxation of photoexcited nanosystems is a fundamental process of light-matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free- electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental pho- toelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He ) within 1 ps. Subsequently, the bubble collapses and releases metastable He at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses

Soft Chemical Control of Superconductivity in Lithium Iron Selenide Hydroxides Li1–x_{1–x}Fex_x(OH)Fe1–y_{1–y}Se

Hydrothermal synthesis is described of layered lithium iron selenide hydroxides Li$_{1–x}$Fex(OH)Fe$_{1–y}$Se (x$\sim$0.2; 0.02 < $y$ < 0.15) with a wide range of iron site vacancy concentrations in the iron selenide layers. This iron vacancy concentration is revealed as the only significant compositional variable and as the key parameter controlling the crystal structure and the electronic properties. Single crystal X-ray diffraction, neutron powder diffraction, and X-ray absorption spectroscopy measurements are used to demonstrate that superconductivity at temperatures as high as 40 K is observed in the hydrothermally synthesized samples when the iron vacancy concentration is low ($y$ < 0.05) and when the iron oxidation state is reduced slightly below +2, while samples with a higher vacancy concentration and a correspondingly higher iron oxidation state are not superconducting. The importance of combining a low iron oxidation state with a low vacancy concentration in the iron selenide layers is emphasized by the demonstration that reductive postsynthetic lithiation of the samples turns on superconductivity with critical temperatures exceeding 40 K by displacing iron atoms from the Li$_{1–x}$Fe$_x$(OH) reservoir layer to fill vacancies in the selenide layer

Molecular and electronic dynamics in van der Waals cluster spectroscopy, hydrogen abstraction reactions, and inelastic collisions at liquid surfaces

Quantum mechanical measurements are essential for an understanding of collision and reaction dynamics on the molecular scale. To this end, laser induced fluorescence (LIF) is used to probe rotational, vibrational, and electronic product state distributions following various chemical events. For example, LIF on the hydroxyl radical is employed to examine the propensity to populate different levels of OH following photolysis of H2O molecules using a technique known as vibrationally mediated dissociation (VMD). VMD is also used as an indirect method for obtaining infrared spectra of water clusters (Ar-H2O, H2O-H2O, and H2-H 2O), weakly bound species which are produced in the cold (∼ 5 K) environment of a slit supersonic expansion. Peaks are then assigned with the aid of high level theoretical calculations. LIF is also performed to study systems where reactive precursors produce OH/OD radicals (F + D2O → DF + OD and F + H2O → HF + OH) as well as for nonreactive processes where ground state NO inelastically is scattered from liquid Ga metal or room temperature ionic liquid (RTIL) surfaces. In the reactive scattering experiments, careful examination of OH product spin-orbit branching provides an opportunity to quantify the degree of multiple surface behavior in these systems. Rotational-state-resolved scattering of nitric oxide from a molten metal provides an opportunity to directly observe thermal roughening of the liquid due to capillary wave excitations. Scattered NO electronic distributions, which are out of thermal equilibrium with rotation, are quite sensitive to surface temperature, a possible consequence of interactions with electron-hole pairs during the collision. Finally, NO is scattered from room temperature ionic liquid (RTIL) samples where branching between the two possible scattered spin orbit states (2Π1/2 and 2Π3/2) is found to be highly sensitive to surface heating and choice of ionic liquid. This may serve as a novel means for characterizing these surfaces, which are of technological interest due to their potential role as advanced solvents

Characterization of liquid waste streams from shale gas development

Hydraulic fracturing has been practiced for over thirty years to improve effective porosity and stimulate oil and gas production. In the Appalachian Basin it has been used with horizontal drilling since 2008 to extract methane and natural gas liquids from source rock such as the Marcellus Formation. Hydraulic fracturing generates large volumes of waste water known as flowback: about 3,800 m3/well. Literature regarding the chemical composition of this waste stream is limited. This study examined injected hydraulic fracturing fluid from two wells and flow- back from four hydraulically fractured wells. Wells were sampled at various times during the flowback cycle and in sections of the basin known to produce either wet or dry gas, the former producing higher volumes of natural gas liquids. Concentrations were compared to available literature values and to drinking water standards as a basis for determining which parameters might compromise nearby, domestic wells in the event of an accidental release. Measured parameters included three classes: organic, inorganic ions and radioactive isotopes. Concentrations of all three classes of contaminants tended to increase during the flowback cycle. Organic contaminants including BTEX were substantially higher in the wet gas well. Radioactive isotopes, particularly alpha, beta, radium 226 and radium 228 increased during flowback. All contaminants were found in much higher concentrations in flowback water than in injected hydraulic fracturing fluids suggesting that the bulk of contaminants originate in the Marcellus formation rather than in the injected hydraulic fracturing fluids. Primary and secondary drinking water standards for all classes of contaminants were generally exceeded in flowback water. In addition to summarizing the chemical composition of flowback water, the presentation recommends practices for controlling the risk of environmental exposure