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 Title: Using Computational Chemistry To Design A Pump-probe Scheme For Measuring Nitrobenzene Radical Cation Dynamics Author(s): López Peña, Hugo A. Contributor(s): Tibbetts, Katharine Moore; McPherson, Shane L.; Ampadu Boateng, Derrick Subject(s): Dynamics and kinetics Abstract: Nitrobenzene is often used as a model molecule for the study of the dissociation dynamics of nitroaromatic energetic materials. The potential energy surfaces for the ground cationic state D$_0$ and the first ten excited states D$_1$ through D$_{10}$ were calculated as a function of the C--\chem{NO_2} torsional angle using time-dependent density functional theory. These surfaces were employed in the prediction of the most efficient probe wavelength for femtosecond time-resolved mass spectrometry measurements. It was found that the D$_0\rightarrow$ D$_4$ transition in nitrobenzene cation has a geometry-dependent oscillator strength, reaching a maximum at 90$^\circ$ C--\chem{NO_2} torsional angle, with a corresponding energy gap of $\sim$2 eV. These results are consistent with the experimental observation of a vibrational wave packet along the C--\chem{NO_2} torsional mode in nitrobenzene cation. Time-resolved measurements using a probe wavelength of 650 nm, nearly resonant with the strong D$_0\rightarrow$ D$_4$ transition, result in enhanced ion yield oscillation amplitudes as compared to excitation with the nonresonant 800 nm wavelength. These results demonstrate that computational chemistry can predict the best choice of probe wavelength in time-resolved measurements of vibrational coherent states in molecular cations. Issue Date: 2021-06-22 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111306 DOI: 10.15278/isms.2021.TC07 Date Available in IDEALS: 2021-09-242022-01-21
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