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Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

Authors :
Stein, Tamar
Stein, Tamar
Bandyopadhyay, Biswajit
Troy, Tyler P
Fang, Yigang
Kostko, Oleg
Ahmed, Musahid
Head-Gordon, Martin
Stein, Tamar
Stein, Tamar
Bandyopadhyay, Biswajit
Troy, Tyler P
Fang, Yigang
Kostko, Oleg
Ahmed, Musahid
Head-Gordon, Martin
Source :
Proceedings of the National Academy of Sciences of the United States of America; vol 114, iss 21, E4125-E4133; 0027-8424
Publication Year :
2017

Abstract

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2) n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Details

Database :
OAIster
Journal :
Proceedings of the National Academy of Sciences of the United States of America; vol 114, iss 21, E4125-E4133; 0027-8424
Notes :
application/pdf, Proceedings of the National Academy of Sciences of the United States of America vol 114, iss 21, E4125-E4133 0027-8424
Publication Type :
Electronic Resource
Accession number :
edsoai.on1287346187
Document Type :
Electronic Resource