High-resolution anion photoelectron spectra of cryogenically cooled (Formula presented.), (Formula presented.), and (Formula presented.) obtained using slow photoelectron velocity-map imaging (cryo-SEVI) are presented, providing insight into the geometries, energetics, and vibronic structure of the anionic and the neutral clusters. These spectra yield accurate vibrational frequencies for the neutral clusters. They also yield refined adiabatic detachment energies (ADEs) for the ground states of (Formula presented.) and (Formula presented.) of 1.5374(6) eV and 1.9019(4) eV, respectively, while the ADE of a low-lying isomer of (Formula presented.) is found to be 1.9050(7) eV. The cryo-SEVI spectra show that the ground state of (Formula presented.) is a distorted trapezoid, and represent the first confirmation of the distorted trapezoid structure of (Formula presented.), the only low-lying isomer of this cluster with a permanent dipole moment. Additional transitions are observed from two low-lying anion isomers: a linear structure and a rhombus. The spectrum of (Formula presented.), in combination with electronic structure calculations, suggests that the true ground state of (Formula presented.) is a ring structure with a transannular C–C bond, addressing a longstanding controversy surrounding this cluster. All three spectra exhibit Franck-Condon forbidden transitions; these are attributed to Herzberg-Teller coupling in (Formula presented.) and (Formula presented.) and autodetachment from an excited electronic state of (Formula presented.).
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Photoelectron spectroscopy
- ion spectroscopy