Identification of the fragment of the 1-methylpyrene cation by mid-IR spectroscopy.

The fragment of the 1-methylpyrene cation, is expected to exist in two isomeric forms, 1-pyrenemethylium and the tropylium containing species We measured the infrared (IR) action spectrum of cold tagged with Ne using a cryogenic ion trap instrument coupled to the FELIX laser. Comparison of the experimental data with density functional theory calculations allows us to identify the isomer in our experiments. The IR Multi-Photon Dissociation spectrum was also recorded following the CH loss channel. Its analysis suggests combined effects of anharmonicity and isomerisation while heating the trapped ions, as shown by molecular dynamics simulations.