Lyman α photolysis of solid nitromethane (CH₃NO₂) and D3-nitromethane (CD₃NO₂) – untangling the reaction mechanisms involved in the decomposition of model energetic materials

Abstract

Solid nitromethane (CH3NO2) along with its isotopically labelled counterpart D3-nitromethane (CD3NO2) ices were exposed to Lyman α photons to investigate the mechanism involved in the decomposition of energetic materials in the condensed phase. The chemical processes in the ices were monitored online and in situ via infrared spectroscopy complimented by temperature programmed desorption studies utilizing highly sensitive reflectron time-of-flight mass spectrometry coupled with pulsed photoionization (ReTOF-PI) at 10.49 eV. The infrared data revealed the formation of cis-methylnitrite (CH3ONO), formaldehyde (H2CO), water (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Upon sublimation of the irradiated samples, three classes of higher molecular weight products, which are uniquely formed in the condensed phase, were identified via ReTOF-PI: (i) nitroso compounds [nitrosomethane (CH3NO), nitrosoethane (C2H5NO), nitrosopropane (C3H7NO)], (ii) nitrite compounds [methylnitrite (CH3ONO), ethylnitrite (C2H5ONO), propylnitrite (C3H7ONO)], and (iii) higher molecular weight molecules [CH3NONOCH3, CH3NONO2CH3, CH3OCH2NO2, ONCH2CH2NO2]. The mechanistical information obtained in the present study suggest that the decomposition of nitromethane in the condensed phase is more complex compared to the gas phase under collision-free conditions opening up not only hitherto unobserved decomposition pathways of nitromethane (hydrogen atom loss, oxygen atom loss, retro carbene insertion), but also the blocking of several initial decomposition steps due to the 'matrix cage effect'.

A photoionization mass spectroscopic study on the formation of phosphanes in low temperature phosphine ices

“…[15][16][17][18][19][20][21][22][23][24] Briefly, a silver mirror substrate is mounted onto a rotatable cold finger made of oxygen-free high-conductivity copper (OFHC) cooled to 5.5 K AE 0.1 by a closed-cycle helium refrigerator (Sumitomo Heavy Industries, RDK-415E). [15][16][17][18][19][20][21][22][23][24] Briefly, a silver mirror substrate is mounted onto a rotatable cold finger made of oxygen-free high-conductivity copper (OFHC) cooled to 5.5 K AE 0.1 by a closed-cycle helium refrigerator (Sumitomo Heavy Industries, RDK-415E).…”

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…Since the methyl radical was not detected, and only carbene has been inferred via its methane counter fragment (reaction (3)), the experiments suggest that propane is formed via reaction of ethane and carbene insertion (reaction (13)). Note that in related experiments of a nitromethane (CH 3 NO 2 ) radiolysis, carbene (CH 2 ) was also identified as a crucial growth species leading from methyl nitrite (CH 3 ONO) to ethyl nitrite (C 2 H 5 ONO) and from nitrosomethane (CH 3 NO) to nitrosoethane (C 2 H 5 NO) (Kaiser & Maksyutenko 2015a, 2015bMaksyutenko et al 2015;Tsegaw et al 2016;Turner et al 2016). The even-numbered alkanes detected require C2 building blocks, i.e., ethylene and/or the ethyl radical.…”

“…The present study employs an alternative method of tunable photoionization coupled with reflectron time-of-flight mass spectrometry (PIReTOF-MS) to unravel the complex chemistry taking place in the irradiated ethane ices. The incorporation of fragment-free single photon soft photoionization utilizing tunable vacuum ultraviolet light (VUV) has previously demonstrated the feasibility of this approach (Jones & Kaiser 2013;Kaiser et al 2014Kaiser et al , 2015Maity et al 2014aMaity et al , 2014bMaity et al , 2015Förstel et al 2015;Maksyutenko et al 2015;Turner et al 2015Turner et al , 2016Abplanalp et al 2016). The products released into the gas phase are photoionized and sampled via a reflectron time-offlight mass spectrometer, which monitors the complete product spectrum simultaneously based on the mass-to-charge ratios of the neutral molecules after their ionization.…”

“…Furthermore, the concurrent monitoring of both the ice (FTIR) and gas phases (PI-ReTOF-MS) allows for a cross correlation of the data to extract more accurately which infrared peaks belong to which molecule based on their appearance in the PI-ReTOF-MS data and decline in the FTIR spectra. In summary, PI-ReTOF-MS coupled with FTIR has been established as a powerful tool fordetecting the complete inventory of molecules formed in laboratory astrophysics experiments (Jones & Kaiser 2013;Kaiser et al 2014Kaiser et al , 2015Maity et al 2014aMaity et al , 2014bMaity et al , 2015Förstel et al 2015;Maksyutenko et al 2015;Turner et al 2015Turner et al , 2016Abplanalp et al 2016). References.…”

Understanding the Reactivity and Regioselectivity of Methylation of Nitronates [R1R2CNO2]− by CH3I in the Gas Phase

“…27,28 Calculations of the enthalpies of deprotonation of nitroalkanes 19 and the vibrational frequencies of CH 3 NO 2 were compared with the experimental values 29,30 to ascertain the reliability of MP2 and DFT methods (Tables S1 and S2 of the Supporting Information). Indeed, the overall results provided by the MP2 method with medium to large basis sets are in excellent agreement with the experiment.…”