A high-resolution photoelectron imaging and theoretical study of CP^- and C₂P

The discovery of interstellar anions has been a milestone in astrochemistry. In the search for new interstellar anions, CP^- and C₂P^- are viable candidates since their corresponding neutrals have already been detected astronomically. However, scarce data exist for these negatively charged species. Here we report the electron affinities of CP and C₂P along with the vibrational frequencies of their anions using high-resolution photoelectron imaging. These results along with previous spectroscopic data of the neutral species are used further to benchmark very accurate quartic force field quantum chemical methods that are applied to CP, CP^-, C₂P, and two electronic states of C₂P^-. The predicted electron affinities, vibrational frequencies, and rotational constants are in excellent agreement with the experimental data. The electron affinities of CP (2.8508 ± 0.0007 eV) and C₂P (2.6328 ± 0.0006 eV) are measured accurately and found to be quite high, suggesting that the CP^- and C₂P^- anions are thermodynamically stable and possibly observable. The current study suggests that the combination of high-resolution photoelectron imaging and quantum chemistry can be used to determine accurate molecular constants for exotic radical species of astronomical interest.