Size selective spectroscopy

Yanes et al. (2004) observed a very interesting size selective spectroscopy in 0.4 mol% Eu3+ SnC>2 nanocrystals ( 4 nm) embedded in SiC>2 glass prepared by thermal treatment of sol-gel glasses. The mean size of SnC>2 nanocrystals is comparable to the bulk exciton Bohr radius (4.8 nm). Thus the band-gap excitation energy depends on the nanocrystal size. 

Wang L S, Cheng H S and Fan J 1995 Photoeieotron spectroscopy of size-selected transition metal clusters Kc , n = 3-24 J. Chem. Phys. 102 9480... 

According to absorption spectroscopy, these nanoribbons were composed of 3R-M0S2. The E/C synthesis of M0S2 wires and ribbons was size selective control over the wire or ribbon size was provided by control of the MoO , nanowire dimensions, which in turn were controlled using the electrodeposition potential and time in the first step of the synthesis. 

Buch, U. and Huisken, F. (2000) Infrared spectroscopy of size-selected water and methanol clusters. Chem. Rev., 100, 3863-3890. 

Infrared spectroscopy is the workhorse in this field, because it can quickly provide dynamical details, discriminate between different cluster sizes and phases [40], and sample a wide spectral range. It often yields valuable feedback for quantum chemical calculations. In contrast to some action spectroscopy techniques, IR absorption spectroscopy is not intrinsically size-selective. All cluster sizes generated in the expansion are observed together, and indirect methods of size assignment are needed. 

Y. Matsuda, M. Hachiya, A. Fujii, and N. Mikami, Stimulated Raman spectroscopy combined with vacuum ultraviolet photoionization Application to jet cooled methanol clusters as a new vibrational spectroscopic method for size selected species in the gas phase. Chem. Phys. Lett. 442, 217 219 (2007). 

C. Steinbach, M. Famik, I. Ettischer, J. Siebers, and U. Buck, Isomeric transitions in size selected methanol hexamers probed by OH stretch spectroscopy. Phys. Chem. Chem. Phys. 8, 2752 2756 (2006). 

F. Huisken. chapter Infrared spectroscopy of size-selected free and... 

Figure 1. Experimental set-up for performing transient two-photon ionization spectroscopy on metal clusters. The particles were produced in a seeded beam expansion, their flux detected with a Langmuir-Taylor detector (LTD). The pump and probe laser pulses excited and ionized the beam particles. The photoions were size selectively recorded in a quadrupole mass spectrometer (QMS) and detected with a secondary electron multiplier (SEM). The signals were then recorded as a function of delay between pump and probe pulse.

We have discussed recent computational and spectroscopic results on the photoinduced hydrogen transfer and proton transfer chemistry in hydrogen-bonded chromophore-solvent clusters. The interplay of electronic spectroscopy of size-selected clusters and computational studies has led to a remarkably detailed and complete mechanistic picture... 

The Buck method is most useful for medium sized clusters, and in experiments that do not attempt detailed photochemical studies of the size selected clusters. High resolution spectroscopy of the selected clusters is impractical because the number per quantum state is small, due to the many occupied ro-vibrational... 

Abstract Makrolon , a commercially available polycarbonate with a glassy ultramicroporous structure (mean pore-volume 0.1 nm3), was often employed as sensitive layer for optical sensors in recent years. Due to the definite pore volume-distribution, it can be used as a size-selective sensitive layer. The interaction behaviour of Makrolon of different layer-thicknesses under the influence of methanol, ethanol and 1-propanol is characterized by Spectral El-lipsometry (SE), Surface Plasmon Resonance Spectroscopy (SPR)... 

Huisken, R, Kaloudis, M., and Kulcke, A., Infrared spectroscopy of small size-selected water clusters, J. Chem. Phys. 104, 17-25 (1996). 

Most investigations of photoinduced electron transfer have been performed in condensed phases. Much less is known about conditions that permit the occurrence of intramolecular ET in isolated (collision-free) molecular D-A systems. A powerful method for this kind of study is the supersonic jet expansion teehnique (which was originally developed by Kantrowitz and Grey in 1951 [66]) combined with laser-induced fluorescence (LIF) spectroscopy and time-of-flight mass spectrometry (TOF-MS). On the other hand, the molecular aspects of solvation can be studied by investigations of isolated gas-phase solute-solvent clusters which are formed in a supersonic jet expansion [67] (jet cooling under controlled expansion conditions [68] permits a stepwise growth of size-selected solvation clusters [69-71]). The formation of van der Waals complexes between polyatomic molecules in a supersonic jet pro-... 

Following the above-mentioned spectroscopic study by Johnson and co-workers [55], Neumark and co-workers [56] explored the ultrafast real-time dynamics that occur after excitation into the CTTS precursor states of I (water) [n — 4-6) by applying a recently developed novel method with ultimate time resolution, i.e., femtosecond photoelectron spectroscopy (FPES). In anion FPES, a size-selected anion is electronically excited with a femtosecond laser pulse (the pump), and a second femtosecond laser pulse (the probe) induces photodetachment of the excess electron, the kinetic energy of which is determined. The time-ordered series of the resultant PE spectra represents the time evolution of the anion excited state projected on to the neutral ground state. In the study of 1 -(water), 263 nm (4.71 eV) and 790 nm (1.57 eV) pulses of 100 fs duration were used as pump and probe pulses, respectively. The pump pulse is resonant with the CTTS bands for all the clusters examined. 

Iron clusters exhibit facile chemisorption toward methanol, the reaction proceeding with little or no cluster-size selectivity. An interesting feature of this system is that the chemisorption rate constants are nearly identical toward various isotopic sjjecies (CH3OH, CH30D,CD3 0H). If dissociation of a C—H or O—H bond was the initial step, then this should be manifested in an observable kinetic isotope effect. Thus the initial chemisorption step most likely involves the lone-pair orbital localized on the oxygen atom. More extensive studies of the chemistry of the Fe methanol system have been explored using infrared multiple-photon dissociation spectroscopy. These results are discussed in detail in Section Vlll. 

Fig. 1.5. Experimental setup of the high-frequency laser vaporization cluster ion source driven by a 100-Hz Nd Yag laser for the production of ion clusters, ion optics with a quadrupole deflector, and quadrupole mass Alter for size-selection and deposition the analysis chamber with a mass spectrometer for thermal desorption spectroscopy (TDS), a Fourier transform infrared spectrometer, a spherical electron energy analyzer for Auger electron spectroscopy (AES) for in situ characterization of the clusters [73]...

The mechanistic details for the combustion of CO on supported gold clusters are discussed next. Small gold clusters, Au (n < 20) were deposited after size-selection from the gas phase onto defect-poor and defect-rich MgO(lOO) films. As described in Sect. 1.5.1, defect-rich films are characterized by a given density ( 5% ML) of extended defects and point defects (F centers), whereas for defect-poor films the density of F-centers is negligible. The CO-oxidation was studied by combined temperature programmed reaction (TPR) and Fourier transform infrared spectroscopy and the obtained results were compared to extensive ab initio calculations [209,368,369]. 

Various experimental methods used to investigate the H-bonded clusters in gas phase are described in the earlier reviews [150-152]. Since molecular clusters are produced in supersonic beams in the gas phase under collision free conditions, they are free from perturbation of many-body interactions. The spectroscopic characterization of these clusters has less complexity. Hence, high level quantum chemical calculations on these clusters can be directly compared with the experimental values. Due to advent of laser-based techniques, it is currently possible to study the size and mass selective molecular clusters produced in supersonic beam. The combination of high resolution spectroscopy along with the mass and size selective strategies has enabled the scientific community to look at the intrinsic features of H-bonding. Principles behind the method of size selection, beam spectroscopy, and experimental setup have also been thoroughly described in an earlier thematic issue in chemical review [105, 150-152]. 

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