Cluster excitation

Fig. 9 Antibunched luminescence from a single Au23 cluster, excited at 632.8 nm. Photons arriving at each of two detectors show a decreased probability of two photons arriving simultaneously (at zero interphoton delay) [1]...

CLUSTER FORMATION AND CLUSTER EXCITATION BY POWERFUL LASERS... 

DOWNHILL V- Z WAVEPACKET MOTION IN TDMAE Ar CLUSTERS, EXCITED AT 266 nm AND PROBED AT 800 nm... 

PhOH (NH3) PhO (NH3)nH+ But we have recently unambigously proved that the reaction is a neutral hydrogen transfer [8-11] PhOH (NH3) — PhO + (NH3) H by monitoring the ionisation of metastable radicals (NH3)nH several hundreds ns after clusters excitation when initially excited PhOH (NH3)n have totally decayed. 

From the three decay times, which each measurement provides, the main point of interest how is the type I quantity T. It characterizes the dynamics of the relevant electronic state of the cluster size under investigation. The data, therefore, allow us to determine directly the photodissociation probabilities 1/r 1 of the observed clusters excited at the energies of the photon irradiation. The corresponding results reflect the stability of the clusters, as graphically presented in Fig. 26. For all measured cluster sizes the fragmentation probabilities at E = 2.00 eV are smaller than those for the other photon energies (figs. 26a, b). For E = 2.00 eV and E = 2.94 eV the curves of the dependence of the photodissociation probability on the cluster size have similar shapes. In Fig. 26b both curves show a particular instability for Kg, which... 

For the 7HQ-A3 cluster, excitation of ammonia-wire vibrations induces the photoreaction at a threshold of about 200 cm-1 [52], The reaction proceeds by tunnelling, as shown by deuteration of the wire (ND3). It has been found that substitution of NH3 by one, two or three H20 molecules in the wire increases the threshold with each additional water molecule, up to about 2000cur1 in the 7HQ-W3 cluster [15,55],... 

Phenol(NH3) or phenol(MEA) clusters exhibit the same kind of spectroscopic behavior (Jouvet et al. 1990 Solgadi et al. 1988). Excitation spectra of the smallest clusters (n > 3) are well structured and show emission spectra matching that of phenol. Larger clusters excitation spectra become broad and the emission spectra become more typical of that of the phenolate anion (see Figure 4-13). 

Figure 4-13. Fluorescence spectra of phenol(MEA) clusters (MEA = monoethylamine). The spectra of the clusters (full line) were obtained by measurement of the fluorescence cut by a series of filters, (a) Fluorescence of phenol(MEA) with n <2 (excitation wavelength 280.9 nm). For comparison, the fluorescence spectrum in a solution of phenol in ethanol (excitation wavelength = 280 nm) is represented by a dashed line, (b) Fluorescence spectrum for a larger phenol(MEA) clusters (excitation wavelength = 281.5 nm). The fluorescence spectrum in a solution of phenolate anion in NaOH 10-4 mol P1 in ethanol is represented by a dashed line. The maxima of these curves have been normalized to unity. The mass spectra of the clusters corresponding to these excitation conditions are given in the lower part of the figure.

Figure 4-18. Energy diagram for phenol(NH3) for a cluster size of n s 5. The excitation scheme shows how delayed ionization by X2 can produce cluster ions in the outer potential well for reactive PhOH B clusters excited by ).y (from Steadman and Syage 1991).

Figure 5-9. TRSEP signal for the aniline(N2)i cluster. Excitation laser is tuned to the TJj transition, and the probe laser is tuned to the I 6a transition. This plot shows the extent to which the probe pulse diminishes the total fluoresence. The time axis is the difference between the arrival times of the pump and probe pulses. The maximum diminution of the fluorescence is about 30%. The smooth curve is generated using the results of a nonlinear fitting routine. The fast component time constant is 200 + 50 ps.

Figure 5-13. Time resolved 1 + 1 ionization signal scan of the l-naphthol(NH3)3 cluster. Excitation energy, 31,100 cm" ionization energy, 29,000 cm-1. 0, data, solid line, fit. The fit parameters are instrument limited rise followed by a biexponential decay = 60 ps and r2 = 500 ps.

Gwaltney SR, Nooijen M, Bartlett RJ (1996) Simplified methods for equation-of-motion coupled-cluster excited state calculations. Chem Phys Lett 248 189-198. 

Migration clusters may be defined by intermediate-range interactions ( ). These give rise to intermediate-range bonds and clusters ("secondary clusters"). Excitation delocalization will usually happen within "primary clusters", defined by near neighbor interactions. 

In the preceding sections we have outlined the requirements a cluster has to fulfill in order to dissociatively chemisorb H in summary, the cluster first has to contain at least one atom with a d occupation including at least one open d-orbital. Second, there has to be at least one open shell valence (s-character) orbital in the cluster wave-function. If there is only one open shell orbital, a dihydride or possibly a molecularly chemisorbed state will be formed. If there are at least two open shell orbitals, atomically chemisorbed hydrogen atoms of the type found on surfaces will be formed. The formation of the latter state is normally more exothermic. Finally, if these requirements are not fulfilled by the ground state wave-function of the cluster, excitation to a low lying state which satisfies the requirements and which has an excitation energy less than the exothermic ty 20 kcal/mol) will lead to... 

Hence, in a benzene-iodine cluster, excitation at 266 nm leads to the charge-transfer potential energy surface. Using femtosecond excitation one can detect the decay of the initially populated state, the appearance of the products and their kinetic energy distribution and alignment (with respect to the pump laser) ]55, 56,... 

From the point of view of general methodology, several comments are in order. First, the appearance of the Fourier-Bessel transform in the stmcture function [Eq. (20)] reflects on the breakdown of translational invariance, which is prevalent in the case of the bulk. Second, the different symmetries of spherically projected structure functions for the finite system and of plane wave structures for the bulk system are crucial for a proper representation of the cluster excitations. Third, the discrete eigenvectors k n are determined by the boundary conditions. Fourth, the energies kin) are discrete. However, the complete spectrum for a fixed value of n containing 1 = 0, 1, 2,... branches would form a continuous smooth curve. 

This classical result, which manifests a minimum value of where the maximal value of Sim is attained, does not correspond to elementary excitations in a quantum cluster. Indeed, collective, large k>A cluster excitations will also be manifested in classical clusters. As in the case of the bulk systems discussed above, such collective excitations in classical clusters will be dissipated, while the roton cluster excitations will be robust with respect to dissipation into lower energy excitation (e.g., phonons). 

Let us start with a qualitative understanding of the main optical effects. Clearly, in non-spherical silver islands (as mainly occurring at low deposition temperatures), the plasmon excitation may be accomplished along different axes of the cluster. Excitations parallel to the longer axis of a prolate cluster lead to light absorption at... 

The method was generalized for an arbitrary number of atonrs [D. Blume, and C.H. Greene, Monte Carlo Hyperspherical Description of Helium Cluster Excited Stated , 2000]. 

Calculations on Complexes, Dimers, Clusters, Excited States. - Mar-oulis has used his finite-field technique to explore the hyperpolarizabilities of the rare gas diatoms Hc2, Nc2, At2 and Kt2 and the interaction hyperpolarizability of hydrogen fluoride with a neon atom. 

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