Fast-beam studies of free-radical photodissociation: the CH2NO2 radical

David J. Leahy; Douglas R. Cyr; David L. Osborn; Daniel M. Neumark

doi:10.1117/12.143115

22 April 1993 Fast-beam studies of free-radical photodissociation: the CH2NO2 radical

David J. Leahy, Douglas R. Cyr, David L. Osborn, Daniel M. Neumark

Proceedings Volume 1858, Laser Techniques for State-Selected and State-to-State Chemistry; (1993) https://doi.org/10.1117/12.143115
Event: OE/LASE'93: Optics, Electro-Optics, and Laser Applications in Scienceand Engineering, 1993, Los Angeles, CA, United States

Abstract

We report a study of the photodissociation of the nitromethyl radical utilizing a fast beam photofragment translational spectrometer. A fast radical beam is prepared via the synthesis, acceleration and subsequent photodetachment of mass-selected, internally cold nitromethyl anions. Following ultraviolet photodissociation, the recoiling photofragments are detected in coincidence by a microchannel plate detector with a time- and position-sensitive wedge-and- strip anode. The data reveal that the electronically excited nitromethyl radicals dissociate into two mass channels: (I) CH₂NO₂$DAG yields CH₂NO + O, and (II) CH₂NO₂$DAG yields CH₂O + NO. The branching ratio of the two channels is nearly constant at 1:1 over the excitation wavelength range of 240 - 270 nm. The kinetic energy release (KER) of channel (I) peaks at 5 - 8 kcal/mol, suggesting that the N-O bond rupture does not occur directly, as it would on a purely repulsive potential surface. The observed KER for channel (II) peaks at 52 kcal/mol, with an average of over 100 kcal/mol going into internal degrees of freedom in the fragments. This channel requires a significant rearrangement of the nuclei and has a large exit barrier. The photofragment angular distributions for both channels show little anisotropy. The absence of the channel corresponding to C-N bond rupture provides evidence that the accessed excited state(s) of nitromethyl have C-N double bond character. These observations provide qualitative information about the mechanisms for O atom loss and for rearrangement and subsequent NO elimination.

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David J. Leahy, Douglas R. Cyr, David L. Osborn, and Daniel M. Neumark "Fast-beam studies of free-radical photodissociation: the CH2NO2 radical", Proc. SPIE 1858, Laser Techniques for State-Selected and State-to-State Chemistry, (22 April 1993); https://doi.org/10.1117/12.143115

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