Unimolecular Dissociation of H&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;&amp;lt;sub style=&amp;quot;margin-left:-6px;&amp;quot;&amp;gt;2n+1&amp;lt;/sub&amp;gt; Hydrogen Clusters: Measured Cross Sections and Theoretically Calculated Rate Constants

Mohamed Tabti,Adil Eddahbi,Said Ouaskit,Lahcen El Arroum,Soufiane Assouli

doi:10.4236/wjcmp.2013.34035

Abstract

In this paper, we studied the process of dissociation unimolecular of the evaporation of H+2n+1 hydrogen clusters according to size, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constants k(E) were determined with the use of statistical theory of unimolecular reactions using various approximations. In our work, we used the products frequencies instead of transitions frequencies in the calculation of unimolecular dissociation rates obtained by three models RRKM. The agreement between the experimental cross section ratio and calculated rate ratio with direct count approximation seems to be reasonable.

Highlights

Unimolecular dissociation [1] is a powerful tool to probe experimentally the physical free clusters
The dissociation of occurs if the energy of vibration along the reaction coordinate exceeds the activation energy, i.e., the barrier height. The probability of this event can be calculated using the statistical approach of the RRKM theory
The available internal energy is the part of the excitation energy beyond the ionization threshold, which is converted to vibration energy

Summary

Introduction

Unimolecular dissociation [1] is a powerful tool to probe experimentally the physical free clusters. Since clusters are particles of finite size, one is confronted with the general question of how to detect and/or characterize such a transition in a finite system, a question of interest for many microscopic or mesoscopic systems, for instance, melting and vaporization of metallic clusters, and nuclear liquid-to-gas transition [14,15,16]. In small systems such as two colliding nuclear or molecular systems fluctuations may wash out the signature of the phase transition [17]. It has been demonstrated theoretically in Ref. [6] and experimentally [18,19,20] that finite systems may exhibit critical behavior to be seen when studying inclusive fragment size distributions, scaled factorial moments, and anomalous fractal dimensions.

Methods

Results

Conclusion