Unimolecular dissociation of cluster ions

EXPERIMENTAL APPROACHES TO THE UNIMOLECULAR DISSOCIATION OF GASEOUS CLUSTER IONS... 

Unimolecular Dissociation of Caseous Cluster Ions CHjO- + CHjOH... 

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. 

Tholmann, D Tonner, D.S., McMahon, T.B. (1994) Spontaneous Unimolecular Dissociation of Small Cluster Ions, (HjO ) and C1 (H20) ( =2-4), under Fourier Transform Ion Cyclotron Resonance Conditions. J. Phys. Chem. 98 2002-2004. 

TYiolmann, D. Tonner, D. S. McMahon, T. B. Spontaneous unimolecular dissociation of small cluster ions, (H30+)L(n) and Cl-fHjOXn) (n = 2-4), under Fourier transform ion cyclotron resonance conditions. J. Phys. Chem. 1994, 98, 2002-2004. 

An example of the usefulness of the reflectron technique discussed earlier in this chapter is evident for the case of ammonia clusters in Figures 3b and c. Upon ionization, ammonia undergoes an internal ion-molecule reaction leading to protonated cluster ions, and concomitant evaporative unimolecular dissociation. This can be viewed in the context of equations 7-9 and the following ... 

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