species are important intermediates in the formation of large carbonaceous molecules. Mass‐selected threshold photoelectron spectra (TPES) of l‐CH, HCH, and c–CH–CCH were recorded using double‐imaging photoelectron–photoion coincidence spectroscopy. The TPES of l‐CH and c–CH–CCH are reported for the first time. These transient species were generated in situ by hydrogen abstraction from cyclopropylacetylene and 1,3‐pentadiyne by fluorine atoms in a discharge flow‐tube reactor. Supported by ab initio calculations and Franck–Condon simulations, unambiguous assignments were achieved, enabling accurate determination of adiabatic ionization energies. The CH results show that hydrogen abstraction from structurally distinct precursors leads to similar isomeric distributions. More generally, the high‐resolution TPES fingerprints reported here provide reliable discrimination between linear and cyclic CH isomers, which is not possible using only photoion yields, offering robust benchmarks for identifying reactive hydrocarbon intermediates in combustion and astrochemical environments.
Jacovella et al. (Tue,) studied this question.