Electron attachment to molecular clusters by collisional charge transfer More About This Article Electron Attachment to Molecular Clusters by Collisional Charge Transfer

557 modes whose density is reduced upon crystallite formation. Conclusion The above analysis of low-temperature absorption data confirms earlier reasoning that a tetracene glass formed by vapor condensation onto a cold substrate can serve as a model system for diagonal disorder. The inhomogeneous broadening of the absorption lines reflects the statistical positional disorder within the environment of an excited molecule. Observation of site splitting derived from the Davydov splitting in the crystalline counterpart structure demonstrates that off-diagonal disorder due to the variation of the exciton transfer integrals is comparatively small even in glasses formed near 4.2 K. The implication of this result is that transfer rates of electronic energy and, by analogy, also charge carriers should be described reasonably well by the product of a coupling factor characterizing electronic intersite coupling in the discrete lattice and an energy matching factor which in the case of an upward jump is simply the Boltzmann factor. This explains the success of applying recent computer simulations based on the above premises to transport phenomena in real syst e m~? *~~ The consistency between model predictions and experimental results also suggests that absorption measurements may be applied to predict the diffusion constant of a charge carrier in an organic single-component glass thereby making use of the common origin of the splitting of exciton and charge carrier transport bands in an amorphous organic solid. Endoergic charge transfer via A + X, -A+ + X,-in single collisions is used to study electron attachment to weakly bound molecular clusters. Two supersonic beams are employed, one to produce fast alkali atoms (usually A = Rb), the other to produce molecular clusters (typically X = Cl, or SO,). From threshold energies for ion-pair formation, nominal electron affinities as a function of cluster size are derived for (ClJ,, C1(C12),-1, and (SO,),, with n = 1-4,2-4, and 1-5, respectively. The collisional charge-transfer process which forms the negative cluster ions occurs on a subpicosecond time scale. The results are interpreted in terms of an impulsive-collision model, with incomplete vibrational relaxation for cluster ions larger than dimers. Introduction Solvated ions govern a host of solution phenomena, but the individual molecular species and processes often cannot be resolved or characterized in condensed phases. This has motivated the recent development of several methods for study of molecular cluster ions in the gas phase. Thermochemical data for solvation of many gaseous ions has been obtained from high-pressure mass spectrometry,lP2 cluster ion formation in flow tubes,3 and photoionizatio