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Most experimental methods for studying the kinetics of surface reactions – for example, temperature programmed desorption (TPD), molecular beam relaxation spectrometry (MBRS) and velocity‐resolved kinetics (VRK) – employ detection schemes that require thermal desorption. However, many adsorbates – for example reaction intermediates – never leave the surface under reaction conditions. In this paper, we present a new method to measure adsorbate concentrations on catalytic surfaces and demonstrate its utility for studying thermal desorption kinetics. After a short‐pulsed molecular beam deposits CO or NH3 on Pt (111), the surface is irradiated with an ultrashort laser pulse that induces desorption. Another tightly focused ultrashort laser pulse ionizes the gas‐phase molecules by a non‐resonant multiphoton process and the ions are detected. This two‐laser signal is then recorded as a function of time after the dosing molecular beam pulse and decays exponentially. First‐order thermal desorption rate constants are obtained over a range of temperatures and found to be in good agreement with past reports. Ion detection is done mass selectively with ion‐imaging, dispersing the gas phase molecules by their velocities. Since laser‐induced desorption (LID) produces hyperthermal gas phase molecules, they can be detected with little or no background. This approach is highly surface‐specific and exhibits sensitivity below 10−4 ML coverage. Because the signals are linearly proportional to adsorbate concentration, the method can be employed at lower temperatures than VRK, whose signal is proportional to reaction rate. [ABSTRACT FROM AUTHOR]

In this research, a manganese dioxide/multiwalled carbon nanotube (MnO2/MWCNT) was firstly synthesized and characterized and then was applied as an effective sorbent for removing Cu2+ ions from aqueous solution. The effects of initial concentration, temperature, contact time, pH solution, and sorbent dosage were investigated and the optimum value of each was determined. The Langmuir isotherm model, Freundlich model, and Temkin model were used to fit our experimental results. Ultimately, using the Van't Hoff approach, the thermodynamic functions of the intended adsorption phenomenon such as ΔH°ad, ΔS°ad, and ΔG°ad were estimated. [ABSTRACT FROM AUTHOR]

To elucidate the effects of NO2 and H2O molecules on the surface conductivity of hydrogenated diamond film, models of various adsorbates containing different molecular ratio of NO2 and H2O on hydrogenated diamond (100) surfaces were constructed. The adsorption energies, equilibrium geometries of adsorbates, density of states, and atomic Mulliken populations were studied by using first‐principles method. The results showed that H2O molecule in the adsorbate could weaken the interactions between the adsorbates and hydrogenated diamond surface significantly. Compared with H2O molecule, NO2 molecule relaxes more dramatically when adsorbed on hydrogenated diamond surface. In addition, density of states for C(100):H–2NO2, C(100):H–NO2, and C(100):H–NO2 + H2O systems are very similar to each other, which indicates an obvious peak at valence band maximum level for all the three samples. It can be attributed to mainly single occupied molecule orbital of NO2 molecule and slightly C–H bond of C(100):H substrate. When the adsorbates contain one NO2 and two H2O molecules, the peak shifts slightly into valence band, but its intensity increases significantly. All the samples exhibit p‐type surface conductivity when adsorbed with pure NO2 molecules, and the surface conductivity remains as H2O molecules added into the NO2 adsorbate layer. However, for oxygenated diamond surface, very week interactions generate between diamond surface and various adsorbates. All the oxygenated diamond (100) surfaces with various adsorbates containing different NO2 and H2O molecules on it exhibit an insulating property. [ABSTRACT FROM AUTHOR]

This contribution deals with two approaches for localized phenomena in excited many-atom systems. The first approach develops a quantum quasi-classical treatment for the density operator, including all atoms. It is based on a partial Wigner representation and is illustrated with applications to photodissociation of NaI, and to light emission of excited Li interacting with a He cluster. This second application describes the direct dynamics with a time-dependent electronic density matrix, expanded in a basis set of atomic functions. It shows that such an approach can deal with electronically excited many-atom systems involving tens of quantum states and hundreds of classical variables. The second approach makes use of the reduced density operator description for a system in a medium. This allows for dissipative dynamics, which can be instantaneous or delayed. An application is presented for femtosecond photodesorption using a Markovian dissipation and construction of the density operator from density amplitudes, for CO/Cu(001). A second application of a reduced density operator has been made to vibrational relaxation of adsorbates, solving integrodifferential equations to compare delayed, instantaneous, and Markovian dissipation. It is concluded that delayed dissipation is needed at short times and that a Markovian treatment is suitable for the interpretation of cross-sectional measurements that involve long-term dynamics. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]