Molecular Light Control in Rare-Gases Matrices: The HCl Case

Molecular Light Control in Rare-Gases Matrices: The HCl Case

Copyright: © 2014 |Pages: 51
DOI: 10.4018/978-1-4666-4687-2.ch006
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Abstract

Various characteristics and mechanisms of HCl that has been entrapped in rare gas matrices (Ar, Kr, and Xe) are presented with regard to the spectroscopic characterization of exciplexes, cage exits, photo-dissociations, charge transfers, and the harpoonic mechanism. In addition, this chapter sheds light on specific quantum, potential, and reactive behavior of physical-chemical interactions.
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6.1. Introduction

The light-matter interactions in spectroscopically studied processes such as crystallization, excitation, dissociation, pre-dissociation, and decay should be unitarily induced and observed for open systems. Nevertheless, these processes follow the basic scenarios that an entrapped (guest) molecule in a host lattice/cage may undergo through photonic and potential surface competition, as illustrated in Figure 1. Accordingly, the elementary guest-host phenomena may be listed as follows (Schwentner & Chergui 1992; Apkarian & Schwentner 1999):

Figure 1.

Illustrations of various molecular spectroscopic evolution channels from/within a matrix cage: I) exiting the cage by overcoming its barrier; II) tunneling through the cage barrier; III) fragment stabilization within the cage; IV) recombination in an excited molecular state; V) recombination in high vibrational ground states; adapted and redrawn from Schwentner & Chergui (1992)

  • 1.

    Exiting of the guest molecule fragment or ions by overcoming the cage’s barrier, which may occur directly and impulsively or indirectly after scattering at the cage walls (delayed exit);

  • 2.

    Guest exiting by tunneling through the cage barrier;

  • 3.

    The stabilization of guest-host fragments at an equilibrium position defined by the junction between the repulsive surface and the barrier: this process may eventually be followed by fluorescence;

  • 4.

    The cage (germinate) recombines through the excited electronic-vibrational state;

  • 5.

    The cage (germinate) recombines through the vibrational-rotational states of the ground state; in both of the latter two cases, chemiluminescence is to be expected from the near UV to the mid–IR range.

This phenomenology is unfolded here for studying halogen acids (XH, X=Cl, F, I) in rare gas matrices (RGM=Ar, Xe, or Kr) due to the peculiar properties that these chemical-physical systems display through the chemically reactive halogens and chemical-inerting noble elements. Especially, the systems Ar/HCl and Xe/HCl will be under focus with both experimentally observed and quantum mechanical models. In addition to the physical-chemical interaction that is revealed, the van der Waals potential behavior and extension is also revealed and explicated for further paradigmatic use of charge-transfer processes and reactions, which will eventually occur at the chemical–biological level.

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