Unimolecular chemistry of (CH2)-C-center dot-O-C-center dot=O (methylenecarboxyldiradical) and HO-CH=C=O (hydroxyketene) and of the corresponding radical cations and anions in the gas phase

The C2H2O2+ isomers (CH2)-C-.-O-C+=O (1(+.), methylenecarboxyl radical cati on) and HO-CH=CCOO+. (2(+.), hydroxyketene radical cation) are produced in the gas phase and their spontaneous and collision-induced decompositions ar e compared to those of the known glyoxal radical cation, O=CH-CH=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 O-.-CH2-C+=O, loses CO without appreciable reverse-activation energy, and 3(+.) eliminates CO via the ion-dipole compl ex 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 corresp onding neutral species are determined by neutralization of 1(+.)-3(+.) foll owed 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, ke tene 2 mainly survives intact within the same time window, decomposing only to a small extent to H-. + O-.-CH=C=O. The extensive fragmentation observe d upon +NR+ of 3(+.) is shown to occur in the reionization step and primari ly reflects the low decomposition threshold of 3(+.).