Resonance condition transition ions

For an off-resonant dump laser frequency and a resonant pump laser frequency a high ion current is observed, whereas for double-resonance condition no ion current can be measured due to the negligible population of level 2. In Fig. la the calculated ion current and fluorescence signal is shown using the parameters of our recent work [6]. The pump laser frequency was kept in resonance with the transition 2 < — 1 and the dump laser frequency was scanned across the 2 —+ 3 transition. (It should be mentioned that for... 

Electron spin resonance can provide detailed information about free radical (ions) in condensed media. Transitions between the electron spin levels are stimulated by radiation at frequencies satisfying the resonance condition ... 

Among the techniques available to study free radicals or radical ions in solution, electron spin resonance (ESR) stands out as a technique with sufficient resolution to provide detailed information about the identity of the intermediate in question. In an external magnetic field the unpaired electron of such a species can adopt either of two spin orientations, parallel or antiparallel to the field H0. The two orientations are of slightly different energies and transitions between them can be stimulated by applying radiation of a frequency satisfying the resonance condition in Eq. (14) ... 

Thus, in a magnetic-resonance experiment performed on the free ion, transitions may be induced between these levels under the selection rule Mj = 1, giving the resonance condition ... 

Considerable interest in the subject of C-H bond activation at transition-metal centers has developed in the past several years (2), stimulated by the observation that even saturated hydrocarbons can react with little or no activation energy under appropriate conditions. Interestingly, gas phase studies of the reactions of saturated hydrocarbons at transition-metal centers were reported as early as 1973 (3). More recently, ion cyclotron resonance and ion beam experiments have provided many examples of the activation of both C-H and C-C bonds of alkanes by transition-metal ions in the gas phase (4). These gas phase studies have provided a plethora of highly speculative reaction mechanisms. Conventional mechanistic probes, such as isotopic labeling, have served mainly to indicate the complexity of "simple" processes such as the dehydrogenation of alkanes (5). More sophisticated techniques, such as multiphoton infrared laser activation (6) and the determination of kinetic energy release distributions (7), have revealed important features of the potential energy surfaces associated with the reactions of small molecules at transition metal centers. 

Discontinuous Change in Bond Type.5—In molecules and complex ions of certain types continuous transition from one extreme bond type to another is not possible. In order for continuous transition to be possible between two extreme bond types the conditions for resonance between the corresponding structures must be satisfied. The most important of these conditions is that the two structures must involve the same numbers of unpaired electrons. If the two structures under consideration involve different numbers of unpaired electrons, then the transition between the two must be discontinuous, the discontinuity being associated with the pairing or unpairing of electrons ... 

The partial rate factors af and /3f for the a- and /3-positions of thiophene have been calculated for a wide range of electrophilic reactions these have been tabulated (71 AHC(13)235, 72IJS(C)(7)6l). Some side-chain reactions in which resonance-stabilized car-benium ions are formed in the transition states have also been included in this study. A correspondence between solvolytic reactivity and reactivity in electrophilic aromatic substitution is expected because of the similar electron-deficiency developed in the aromatic system in the two types of reactions. The plot of log a or log /3f against the p-values of the respective reaction determined for benzene derivatives, under the same reaction conditions, has shown a linear relationship. Only two major deviations are observed mercuration and protodemercuration. This is understandable since the mechanism of these two reactions might differ in the thiophene series from the benzene case. 

Catalytic reaction conditions or the exposure to reducing environments may lead to the formation of reduced surface metal oxide species. It is generally difficult to obtain good Raman signals for reduced supported metal oxide species because of their low Raman cross-sections. On the other hand, many reduced transition metal ions have electronic absorption bands in the visible regime. Hence, the laser frequency may be tuned to these absorption bands, and resonantly enhanced Raman spectra should be obtained. 

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