The formation of neutral CCCO 2 H and HCCCO 2 molecules from anionic precursors in the gas phase: a joint experimental and theoretical study

Calculations at the CCSD(T)/aug‐cc‐pVDZ//B3LYP/6‐31G(d) level of theory indicate that the anions − CCCO 2 H and HCCCO   2 −are stable species in their singlet states. Upon collision‐induced, vertical one‐electron oxidation under neutralisation‐reionisation ( − NR + ) conditions, they produce the neutral molecules CCCO 2 H and HCCCO 2 , respectively. Some of the CCCO 2 H neutrals should be stable for the duration of the neutralisation‐reionisation experiment (10 −6  s), while others will dissociate to CCCO and OH (requires 125 kJ mol −1 ). In contrast, neutral HCCCO 2 is expected to be much less stable, and dissociate to HCC and CO 2 (37 kJ mol −1 ). Neither CCCO 2 H nor HCCCO 2 is expected to interconvert, or to rearrange to other isomers. The anions − CCCO 2 H and HCCCO   2 −have been formed in the ion source of the mass spectrometer by the reactions between (CH 3 ) 3 SiCCCO 2 H and F − and HCCCO 2 Si(CH 3 ) 3 and F − , respectively. The − NR + spectrum of − CCCO 2 H shows a recovery signal and also indicates that the lowest energy dissociation pathway of neutral CCCO 2 H corresponds to the loss of OH. The − NR + spectrum of HCCCO 2 displays little or no recovery signal, and the spectrum is dominated by the [CO 2 ] + ion. The experimental observations are in agreement with the predictions of the extensive theoretical studies. Copyright © 2005 John Wiley & Sons, Ltd.