Quantum and Classical Monte Carlo and Molecular Dynamics Simulations of the Structures, Photoionization-Induced Fragmentation, and Optical Absorption Spectra of AlArN Clusters

Abstract

Abstract : The theory group at AFRL/PRSP is engaged in an ongoing effort to develop, implement, and test the spectral theory of Schrodinger eigenstates for efficient construction of accurate many-body potential energy surfaces for HEDM systems such as atoms embedded in solid hydrogen. Because good experimental data is available for AlAr(sub N) clusters, they make an excellent test bed for the spectral theory and its computational implementation. We have used the spectral theory method to calculate the ground and low-lying excited states of AlAr(sub N) clusters, subsequently employing these in a sequence of quantum and classical Monte Carlo and classical molecular dynamics simulations to predict their structures, photoionization-induced fragmentation pathways, and optical absorption spectra. These simulations address the key issue of the degree of cluster fragmentation encountered following photoionization of the neutral clusters. The measured data refer to ion mass spectrometric signals of AlAr(sub N-M)(+) fragments detected subsequent to one-photon uv excitation followed by visible one-photon ionization of a distribution of non size-selected parent AlAr(sub N) clusters. Thus, the observed spectrum attributed to AlAr(sub N-M) is actually a superposition of spectra of all parent neutral clusters AlAr(sub N) which produce AlAr(sub N-M)(+) as one of the ionic fragments following the photoionization step.