Mass resolved excitation spectroscopy

The complex formation between ANI and ammonia clusters has been investigated by using mass resolved excitation spectroscopy (MRES), hole burning spectroscopy (HB)268 and IR spectroscopy coupled to different ionization spectroscopies269-271. Rotational spectra of these complexes are not reported yet. Some ab initio calculations on both neutral and ionized complexes are available269 272-274. In this case, the most stable form of the neutral ANI-NH3 complex is a consequence of a hydrogen bond between a NH bond of aniline... 

Laser-induced multiphoton ionization spectroscopy has been applied to the parent, methyl-, and chloro-substituted pyrazines <85ANC29ll). The ions produced by laser photoionization in the supersonic jet are mass-analyzed using a time of flight mass spectrometer, in which the spectra obtained reflect the absorption of the n-n transition. Mass-resolved excitation spectroscopy by laser ionization in the infrared region has also been applied to the conformational analysis of a-alkyl substituted pyrazines <92JA5269). Dynamic and structural properties of electronically excited states of pyrazine have been elucidated from high resolution laser spectroscopy with MHz resolution <88JST(173)201). 

Ferri D, Kumar MS, Wirz R, et al. First steps in combining modulation excitation spectroscopy with synchronous dispersive EXAFS/DRIFTS/mass spectrometry for in situ time resolved study of heterogeneous catalysts. Phys Chem Chem Phys. 2010 12 5634. 

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. 

D. M. Fedor, R. B. Cody, D. J. Burinsky, B. S. Freiser, and R. G. Cooks, "Dissociative Excitation of Gas-Phase Ions. A. Comparison of Techniques Utilizing Ion Cyclotron Resonance Spectroscopy and Angle-Resolved Mass Spectrometry," Int. J. Mass Spectrom. Ion Proc., 39., 55-64 (1981). 

The possibilities of molecular beam spectroscopy can be enhanced by allowing for spectrally resolved fluorescence detection or for resonant two-photon ionization in combination with a mass spectrometer. Such a molecular beam apparatus is shown in Fig. 4.5. The photomultiplier PMl monitors the total fluorescence /r(A.l) as a function of the laser wavelength Xl (excitation spectrum. Sect. 1.3). Photomultiplier PM2 records the dispersed fluorescence spectrum excited at a fixed laser... 

Isomer selectivity At a finer level of discrimination, vdW complexes or clusters of a given size may occur as a distribution of structural isomers. Isomers of van der Waals and H-bonded complexes have been detected by rotationally resolved UV or IR spectroscopy [29-34], as have isomers of vdW solvent clusters with aromatic molecules [34-38]. The ionization potentials of vdW isomers can differ substantially [17,18,39], allowing mass- and isomer-selective electronic spectroscopy to be performed in a mixture of clusters by selective-ionization (SI) two-color R2PI combined with mass spectrometry in a mixture of clusters [17]. This increase in selectivity is quite general and may also be applied in IR-UV and microwave-UV excitation-ionization schemes. 

To observe ultrafast fragmentation of excited alkali clusters the appropriate tool is real-time MPI spectroscopy. This technique allows the mass-selected detection of the ultrafast photodissociation with high sensitivity. In 1992 Gerber and coworkers presented the first femtosecond time-resolved experiments in cluster physics [32, 131, 132], showing differences in the fragmentation behavior of Nan<2i clusters dependent on the excitation at different wavelengths. 

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