Coulomb Explosion Dynamics of Multiply Charged para-Nitrotoluene Cations

Abstract

This work explores Coulomb explosion (CE) dissociation pathways in multiply charged cations of para-nitrotoluene (PNT), a model compound for nitroaromatic energetic molecules. Experiments using strong-field ionization and mass spectrometry indicate that metastable cations PNT2+ and PNT3+ undergo CE to produce NO2 + and NO+. The experimentally measured kinetic energy release from CE upon formation of NO2 + and NO+ agrees qualitatively with the kinetic energy release predicted by computations of the reaction pathways in PNT2+ and PNT3+ using density functional theory (DFT). Both DFT computations and mass spectrometry identified additional products from CE of highly charged PNT q+ cations with q > 3. The dynamical timescales required for direct CE of PNT2+ and PNT3+ to produce NO2 + were estimated to be 200 and 90 fs, respectively, using ultrafast disruptive probing measurements.

Photodissociation Dynamics of the Highly Stable ortho-Nitroaniline Cation

“… 23 − 26 Moreover, the stability of intact ONA 2+ contrasts with the para -nitrotoluene dication, which undergoes Coulomb explosion to form NO 2 + and C 7 H 7 + within 200 fs. 54 To our knowledge, no intact dication has previously been reported experimentally in any nitro-organic energetic molecule or model system, although the TATB dication has been considered in DFT calculations. 55 We note that Coulomb explosion is visible in the NO + and NO 2 + ion signals in Figure 3 , arising from dissociation of multiply charged ONA species.…”

“…The most intense signals in the pump-only spectrum were the parent ONA + and dication ONA 2+ ; no fragment ion had more than 10% yield relative to the intact parent ion, and the total yield of fragment ions (from ONA + , not ONA 2+ ) relative to the yield of intact ONA + was 29%. In contrast, the related nitroaromatic cations exhibit significantly higher fragment yields with yields of individual fragment ions being ∼50–100% of the parent ion yield under similar ionization conditions. − Moreover, the stability of intact ONA 2+ contrasts with the para -nitrotoluene dication, which undergoes Coulomb explosion to form NO 2 + and C 7 H 7 + within 200 fs . To our knowledge, no intact dication has previously been reported experimentally in any nitro-organic energetic molecule or model system, although the TATB dication has been considered in DFT calculations .…”