Theoretical study on potential energy surface of C₃H₃O⁺

The potential energy surface of C₃H₃O⁺, including twenty-two isomers and thirty-four interconversion transition states, is investigated at the B3LYP/6-31G(d,p) and QCISD/6-31G(d,p) (single-point) levels. The energetic order and the thermal stability of C₃H₃O⁺ isomers are determined. It is shown that five energetically low-lying C₃H₃O⁺ isomers (a) CH₂CHCO⁺, (b) c-CHCHC-OH⁺, (c) trans-CHCCHOH⁺, (c') cis-CHCCHOH⁺, and (d) CH₂CCOH⁺ have high thermal stability both towards isomerization and dissociation, among which the O-protonated cyclopropenone isomer (b) lies in the deepest potential well. It is also shown that four high-lying isomers (i) CHCOCH₂⁺, (n) c-COC-CH₃/^-, (o) CHCCOH₂/⁺ and (t) CCCHOH₂/⁺ have moderate thermal stability, while the remaining thirteen ones are thermally unstable either towards isomerization to more stable ones or dissociation into fragments. The calculated results may be helpful for identifying various C₃H₃O⁺ isomers as well as their related deprotonated C₃H₂O isomers, especially the hitherto unknown isomer (b), as well as the deprotonated forms CH₂CCO (propadienone), c-CHCHC-O (cyclopropenone) and CCCHOH (hydroxypropadienylidene) which still remains astrophysically undetected. In addition, the results presented in this article may provide some useful information for discussing the combustion and interstellar chemistry in which the C₃H₃O⁺ potential energy surface is involved.