Radiative associative adduct formation

Several studies have examined the reactions of Mg+" with unsaturated molecules. Under the lower pressure conditions of FT-ICR mass spectrometry, Mg+" reacts with the polycyclic aromatic hydrocarbon, coronene, via a combination of radiative associative adduct formation (equation 16) and electron transfer (equation 17). The latter reaction is 8 times faster, consistent with it being exothermic. Adduct formation (equation 16) also readily occurs in reactions with Theoretical calculations suggest that related radiative... 

Other radiative association reactions of CO which have been invoked to explain the formation of interstellar C3O include those with the abundant interstellar ions C2H2 and C2H3 (27). In this case neutralization of the adduct ions by recombination with electrons requires complete dehydrogenation to yield C3O. 

The kinetics of ion/molecule adduct formation, under the conditions of low-pressure [ion cyclotron resonance (ICR)], is controlled by radiative relaxation the energy released by the complexation can only relax by emission of infrared photons. The link between the strength of the incipient bond and the association rate constants relies on models based on infrared emission for the relaxation of the energy of association [125, 126]. 

However, central to any truly accurate determination of the radiative rate are the integrated absorption (emission) intensities, A", which for gaseous ions are almost completely unknown as are, usually, the vibrational frequencies. Fortunately, however, ab initio and density functional methods have recently been shown to be quite accurate in their predictions of vibrational spectra for a wide variety of systems, and there is no reason to suspect that this accuracy would not carry over to comparable data for gaseous ions. The one caveat must be that the low-frequency modes that are common in cluster ions will be decidedly anharmonic, and prediction of both these frequencies and their intensities may be suspect. However, these modes are not generally expected to be dominant contributors to the overall radiative rate. In addition, standard RRKM procedures can be applied to the unimolecular dissociation of the same adduct ions and, in principle therefore, the overall kinetics of formation of stabilized association complexes can be accurately modeled. 

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