Gas-phase photofragmentation

The gas phase photofragmentation of transition metal cluster complexes is discussed. The information available for the gas phase dissociation of... 

Presently, the gas phase photofragmentation of several transition metal cluster complexes is reviewed. The techniques employed for these gas phase studies rely on sensitive ionization detection and the use of a broad range of excitation energies. 

In conclusion, the gas phase photofragmentation of Co (C0) CCH shows a wavelength dependence that, with the proper selection of wavelength, gives the experimentalist access to a range of interesting unsaturated metal and metal-carbon clusters. 

The endohedral (metal trapped inside the carbon cage) nature of the metallofullerenes has been questioned, but gas phase photofragmentation experiments of ions99,100 and solid-state measurements indicate that the metals are endohedral not exohedral.101 Exohedral metallofullerenes have been prepared in the gas phase but they have different properties to the endohedral metallofullerenes prepared by the arc or laser methods.102-104 The symbol has been used to denote a species inside the fullerene cage and this symbol will be now used to denote endohedral metallofullerenes. 

To determine molecular motions in real time necessitates the application of a time-ordered sequence of (at least) two ultrafast laser pulses to a molecular sample the first pulse provides the starting trigger to initiate a particular process, the break-up of a molecule, for example whilst the second pulse, time-delayed with respect to the first, probes the molecular evolution as a function of time. For isolated molecules in the gas phase, this approach was pioneered by the 1999 Nobel Laureate, A. H. Zewail of the California Institute of Technology. The nature of what is involved is most readily appreciated through an application, illustrated here for the photofragmentation of iodine bromide (IBr). 

Photofragmentation of Transition Metal Cluster Complexes in the Gas Phase... 

CO)1q, Co CCOlpCCHj and 0200113)4 is compared to the well established data base on cluster compounds in condensed phase. The gas phase results are discussed in light of the predictions of electronic structure theory concerning the photofragmentation of these cluster compounds. 

In this paper, the photofragmentation of transition metal cluster complexes is discussed. The experimental information presented concerning the gas phase photodissociation of transition metal cluster complexes comes from laser photolysis followed by detection of fragments by ionization (5.). Ion counting techniques are used for detection because they are extremely sensitive and therefore suitable for the study of molecules with very low vapor pressures (6.26.27). In addition, ionization techniques allow the use of mass spectrometry for unambiguous identification of signal carriers. 

The first quantitative measurement of the distribution of excited atomic states produced in the multiphoton dissociation of a metal carbonyl has been made for Cr(CO)6. Photodissociation does not yield spin- or parity-differentiated states, rather the state distribution appears to be statistical. Photofragmentation dynamics of Cr(CO)6 in the gas phase have been measured and two channels of dissociation revealed. One of these is a rapid predissociation (efficiency 36%) and the other a slow process (efficiency... 

In gas-phase dynamics, the discussion is focused on the TD quantum wave packet treatment for tetraatomic systems. This is further divided into two different but closed related areas molecular photofragmentation or half-collision dynamics and bimolecular reactive collision dynamics. Specific methods and examples for treating the dynamics of direct photodissociation of tetraatomic molecules and of vibrational predissociation of weakly bound dimers are given based on different dynamical characters of these two processes. TD methods such as the direct projection method for direct photodissociation, TD golden rule method and the flux method for predissociation are presented. For bimolecular reactive scattering, the use of nondirect product basis and the computation of the initial state-selected total reaction probabilities by flux calculation are discussed. The descriptions of these methods are supported by concrete numerical examples and results of their applications. 

Photofragmentations of Organosulfur Compounds. - The gas-phase Raman spectra of cyanogen isothiocyanate (NCNCS) and its photolysis product, isocyanogen (CNCN), have been detected in a study of the 266 nm photodissociation of NCNCS. Direct C-S bond cleavage appears to be the most likely pathway for the formation of CNCN. 

The study of photofragmentation and of conformational dynamics of complex polyatomic molecules, such as proteins and polymers, in the gas phase. 

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