Depletion spectroscopy

Stationary spectroscopy on the C and D states of Na3 already indicated the onset of photoinduced fragmentation. Fragmentation becomes more important as the cluster size increases. As a result, nondissociative electronic excitation processes have not yet been observed for free metal clusters larger than trimers [20]. An alternative to conventional spectroscopy of such bound-free transitions was provided by depletion spectroscopy [2]. A deep insight into the dynamics of such photoinduced cluster fragmentation, however, is obtained with ultrafast observation schemes. The principle of such an... 

Weak complexes of ANI with water molecules were investigated using various IR experiments264- 267. Infrared depletion spectroscopy induced by the IR multiphoton decomposition (IRMPD) processes allowed the difference between the structure of the neutral and ionized complexes to be differentiated. 

D. Intermolecular Hydrogen Bonds of Aniline Cation Infrared Depletion Spectroscopy... 

In a similar way, the clusters between aniline or aniline cation and argon (aniline/Ar , n = 1, 2) are studied by infrared spectra of NH2 stretching modes in a supersonic jet, by using infrared depletion spectroscopy and time-of-flight mass spectrometry173. 

The infrared depletion spectroscopy of the aniline/toluene cluster makes it possible to measure the NH2 stretching vibration185. The two main possibilities which are derived from the calculated structure of the aniline/toluene and [aniline/toluene]4 clusters are depicted respectively in 115 and 116. An N—H - it hydrogen bond is the main interaction in both cases. 

Vibrational spectra of aniline/cyclohexane and aniline/benzene clusters investigated by infrared depletion spectroscopy with selective resonance—enhanced multiphoton ionization with time-of-flight mass spectrometry (REMPI-TOF mass spectrometry) show186 an... 

Aniline/NH3 and [aniline/NH3]+ clusters are studied by infrared depletion spectroscopy. In both cases the hydrogen bond is between the NH of the aniline and the lone pair of NH3. In the cation cluster the interaction is much stronger than in the neutral cluster201. 

In infrared depletion spectroscopy of the neutral aniline/pyrrole205 complex, both spectroscopic observation and theoretical calculations indicate the presence of a hydrogen bond between one of the N—H bonds of aniline and the n system of pyrrole, as illustrated in 129. 

Infrared depletion spectroscopy also makes it possible to obtain information about ternary clusters. This is the case of the aniline/water/tetrahydrofuran cluster206. Its calculated structure 130 presents a chain-like structure. 

This operation correlates the ground and excited states on both surfaces. The two-level charge-induced interchange of the conformers can occur on a timescale of a few picoseconds, which is typical for the resonant photoionization process [35], The dynamics of such a process, 0)° -> 1)+1 and 1)° -> 0)+1, is monitored in real time by the change in the anchoring A-N stretch, equal to Av(Au-N) = 145, 165 (due to the appearance of the A-N stretch doublet), and by the disappearance of the vibrational mode -v(N-H - N) (see Table 3) using, e.g. time-resolved picosecond UV/IR pump-probe ionization depletion spectroscopy [35]. 

Time-resolved FTIR spectra of Rh4(CO)12 subjected to 266 nm. irradiation in heptane gave evidence for the formation of two isomeric forms of Rh4(CO)n(solv).144 Vibrational assignments were made to vCO modes for gas-phase rhodium cluster carbonyls using IR multiphoton depletion spectroscopy. For Rhn(CO), vCO was at 1950 2 cm-1 (n = 6), 1960-1965 cm-1 (n = 7-11 13-20).145 TRIR data (vCO) were used to follow the formation of intrinsically chiral clusters Rh6(CO)i4(p,K2-PX), where PX = bidentate bridging ligands diphenyl(benzothienyl)phosphine and related systems.146... 

This section will present two selected examples of electronic spectroscopy on mass-selected metal clusters in the gas phase. In the first example, time-resolved photoelectron spectroscopy is employed to monitor the real time evolution of an electronic excitation leading to the thermal desorption of an adsorbate molecule from a small gold cluster. In the second example, optical absorption-depletion spectroscopy in conjunction with first principles calculations provide insight into the excited state structure of mass-selected metal clusters. 

Yang, X., Dagdigian, P.J. Fluorescence excitation and depletion spectroscopy of the BAr complex Electronic states correlating with the excited valence B(2s2p D) asymptote, J. Chem. Phys. 106 (1997) 6596-6606. 

Fig. 4.22 Experimental setup for the production of He droplets, pick-up of molecules and IR-spec-troscopy of molecules in He droplets, using depletion spectroscopy (P. Toennies, http //wwwuser. gwdg.de/mpisfto/)...

Femtosecond Time-Resolved Fluorescence Depletion Spectroscopy 321... 

Infrared depletion spectroscopy suggests fast vibrational relaxation in the hydrogen-bonded aniline-tetrahydrofiiran (C6H5NH2- OC4H8) complex ... 

Cluster synthesis by supersonic expansion normally yields broad distribution of cluster sizes. The measurement of any size-dependent property depends on the availability of a mass-specific detection scheme [20]. Relatively nondestructive and selective methods for assaying neutral cluster size distributions have been provided by combinations of mass spectrometry with (a) laser techniques (resonant two-photon ionization (R2PI) [21-26], depletion spectroscopy [27]) and (b) helium cross-beam scattering techniques [28]. 

Concerning the observation of wave packet propagation phenomena, the Ka molecule is another promising candidate. Theoretical calculations [82] predicted an electronic state comparable to the Naa B state at about 800 nm. Different, highly sensitive methods, such as MPI and depletion spectroscopy, were applied but failed [83]. However, as presented in Sect. 3.2.5, with femtosecond real-time spectroscopy it is possible to observe both the vibrational and the dissociation dynamics of this system. This, once again, is an example of the complementarity of cw and femtosecond spectroscopy. 

Fig. 3.36. Excited electronic states A, B, B, C, and D of Nas, revealing a pronounced substructure. While A, B, B, and the energetically lower part of the C state were measured by resonant TPl the D and parts of the C state were detected by depletion spectroscopy. The listed lifetimes were estimated by nanosecond pump probe spectroscopy (taken from [369])...

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