High-resolution anion photoelectron spectroscopy of cryogenically cooled 4-atom silicon carbides

Abstract

High-resolution anion photoelectron spectra of cryogenically cooled , , and 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 and of 1.5374(6) eV and 1.9019(4) eV, respectively, while the ADE of a low-lying isomer of is found to be 1.9050(7) eV. The cryo-SEVI spectra show that the ground state of is a distorted trapezoid, and represent the first confirmation of the distorted trapezoid structure of , 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 , in combination with electronic structure calculations, suggests that the true ground state of 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 and and autodetachment from an excited electronic state of .