Dr. Tamar Stein - Theoretical Special Seminar

December 1, 2016
Monday, January 9, 2017 - 4:10pm
McPherson Laboratory 2015
Tamar Stein

Affiliation: University of California, Berkeley

Title: "From ionization of small acetylene clusters to the first aromatic ring: A different path for hydrocarbon growth"

The formation of benzene and its cation constitute a likely gateway to polycyclic aromatic hydrocarbons, which act as the bridge to larger carbonaceous material, such as soot, in combustion processes, and interstellar dust. In my talk, I will present results that address the long-standing puzzle of how ion-molecule reactions involving small unsaturated organics, such as acetylene (which is widespread in the interstellar medium), can lead to benzene cation. I will present new insights into the facile way in which C6H6+ products, including benzene cation, can be accessed after ionization of cold isolated neutral clusters, and show that there is a catalytic role for what are nominally spectator acetylene molecules. The results include ab-initio molecular dynamics (AIMD) simulations and molecular beam vacuum-ultraviolet (VUV) photoionization mass spectrometry experiments, and provide insights into the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). The products in the experiment change from reactive fragmentation products in a higher temperature and higher density gas regime towards a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. I will discuss these changes to the products under different conditions of the VUV experiments. Finally, I will discuss the detailed post-ionization dynamics, as revealed from the AIMD simulations, of the ionized acetylene clusters that can lead to the formation of benzene cation.

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