Unimolecular chemistry of

^"CH₂ OC^"=O (methylenecarboxyldiradical) and HOCH=C=O (hydroxyketene) and of the corresponding radical cations and anions in the gas phase

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Eur. J. Mass Spectrom. 6, 121 - 130 (2000)

Unimolecular chemistry of ^"CH₂ OC^"=O (methylenecarboxyldiradical) and HOCH=C=O (hydroxyketene) and of the corresponding radical cations and anions in the gas phase

Michael J. Polce, Wei Song, Blas A. Cerda and Chrys Wesdemiotis^*
Department of Chemistry, The University of Akron, Akron, OH 44, USA

ABSTRACT:

The C₂H₂O₂^+" isomers ^"CH₂OC⁺=O (1^+", methylenecarboxyl radical cation) and HOCH=C=O^+" (2^+", hydroxyketene radical cation) are produced in the gas phase and their spontaneous and collision-induced decompositions are compared to those of the known glyoxal radical cation, O=CHCH=O^+" (3^+"). At threshold, all three ions yield CH₂=O^+" + CO via unique pathways. 1^+" undergoes direct CO rupture with substantial reverse-activation energy, 2^+", after H-rearrangement to ^"OCH₂C⁺=O, loses CO without appreciable reverse-activation energy, and 3^+" eliminates CO via the iondipole complex ^+"O=CH₂"""CO. The fragmentations of collisionally-activated 1^+"3^+" differ substantially, consistent with these ions being distinct C₂H₂O₂^+" radical cations. Charge reversal of 1^+"3^+" shows that 1^" and 2^" are viable radical anions. The stabilities and reactivities of the corresponding neutral species are determined by neutralization of 1^+"3^+" followed by reionization to either cations (⁺NR⁺) or anions (⁺NR). Diradical 1 is found to be weakly bound by kinetic barriers and dissociates largely in the microsecond time scale to CH₂ + CO₂ and to CH₂=O + CO. In contrast, ketene 2 mainly survives intact within the same time window, decomposing only to a small extent to H^" + ^"OCH=C=O. The extensive fragmentation observed upon ⁺NR⁺ of 3^+" is shown to occur in the reionization step and primarily reflects the low decomposition threshold of 3^+".

Keywords: distonic radical ions, diradicals, ketenes, neutralizationreionization, charge reversal

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