Experimental and Theoretical Studies of Roaming Dynamics in the Unimolecular Dissociation of CH₃NO₂to CH₃O+NO

Abstract

Roaming Reaction / Photochemistry / Theoretical Dynamics / Trajectory Calculations / Potential Energy Surfaces / IsomerizationCharacteristic signatures of roaming are seen in the translational energy distribution and rotational energy distributions in the products CH 3 O + NO from the unimolecular dissociation of nitromethane in both theory and experiment. Calculations on a new global potential energy surface reveal the detailed roaming-isomerization dynamics in this process, and these are supported by the experimental observations. Calculations find a characteristic of roaming, namely production of vibrationally excited CH 3 O, which is consistent with experiment. This continues to challenge the conventional idea in transition state theory of a localized transition state bottleneck that is a cornerstone of chemical reaction theory.

Novel Reaction Mechanisms Pathways in the Electron Induced Decomposition of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2)

“…50,116 The energized nitromethane initially enters the dissociation channel CH 3 ··· NO 2 with the calculated C−N bond length at about 4.58 Å. 114 The incipient fragments reorient and recombine to transiently form the cis-CH 3 ONO isomer via roaming, [35][36][37][38]73,74 which can then result in the molecular and radical fragmentation pathways as discussed above (reaction 4). However, in the ice, the methyl radical and the nitrogen dioxide are trapped within the matrix cage and recombine back either to nitromethane (CH 3 NO 2 ) or methyl nitrite (CH 3 ONO).…”

Roaming Under the Microscope: Trajectory Study of Formaldehyde Dissociation

“…Transition-state theory has been a bedrock method for calculating the rate constants of chemical processes, − yet, at least in its most common form, it is based on the notion that molecular motions predominantly follow a “minimum energy path.” There is increasing evidence that highly excited molecules often bypass this minimum energy path and react in unexpected ways from unexpected geometries. An early, confirmed example of this behavior, often called “roaming,” was stimulated by and speculated about in experimental work on formaldehyde dissociation in the research groups of Moore − and then confirmed by the research groups of Suits − and Bowman. ,− Reviews of this research − and further studies of formaldehyde dissociation and the H + HCO reaction ensued. − Similar roaming behavior has subsequently been found in other unimolecular dissociations, including those of acetaldehyde, − larger aldehydes, methyl formate, − acetone, alkanes, NO 3 , ,, nitromethane, − methyl nitrite, carbon dioxide, and Criegee intermediates . Roaming in bimolecular reactions has also been observed and discussed. − Several reviews of this active area of research have recently appeared. − Consequently, it is now well-established that many systems react via trajectories that deviate strongly from the minimum energy path.…”

Thermal Dissociation and Roaming Isomerization of Nitromethane: Experiment and Theory

“…Nitromethane is an energetic material and monopropellant, and its decomposition has been studied extensively both experimentally − and theoretically. ,,− For a long time there was some disagreement as to whether scission of the C–N bond to produce CH 3 and NO 2 was the sole decomposition reaction. This discord arose from differences found in shock tube and infrared multiphoton dissociation (IRMPD) experiments.…”